Graduate Student Defense Presentations

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Modeling gross primary production of midwest maize and soybean croplands with satellite and gridded weather data - Gunnar Malek-Madani

  • Thesis Defense
  • 4/17/2017

The gross primary production (GPP) metric is useful in determining trends in the terrestrial carbon cycle. Models that determine GPP utilizing the light use efficiency (LUE) approach in conjunction with biophysical parameters that account for local weather conditions and crop specific factors are beneficial in that they combine the accuracy of the biophysical model with the versatility of the LUE model. One such model developed using in situ data was adapted to operate with remote sensing derived leaf area index (LAI) data and gridded weather datasets. The model, known as the EGM model, uses a four scalar approach to account for biophysical parameters including temperature, water stress, light quality, and phenology. This study drives the EGM model using remotely sensed LAI data and gridded weather data for seven locations in the northern Midwest. Results show an increase in error (RMSE = 3.5 g C m-2 d-1) over the previous iteration in which in situ data were used (2.6 g C m-2 d-1). Poor gridded weather atmospheric pressure and incoming solar radiation inputs, increased climatic variation in the study sites, and the application of LAI algorithms calibrated using solely Nebraska sites to sites in Iowa, Minnesota, and Illinois lead to this increased error. Despite this, the study showed there is good correlation between measured and modeled GPP using this model for the field years under study. As the ultimate objective of research is to develop regional estimates of GPP, the decrease in model accuracy is somewhat offset by the model's ability to function with gridded weather datasets and remotely sensed biophysical data. The level to which the error is found to be acceptable is dependent upon the scope and objectives of the research at hand.

Errors in gridded weather data sets and their impacts on estimating reference evapotranspiration - Philip Blankenau

  • Thesis Defense
  • 4/14/2017

Gridded weather data sets are useful for modeling in agriculture, hydrology and ecology. This research explored the error in several gridded weather variables and in reference evapotranspiration computed from those variables. Results show that all gridded data have a tendency to overestimate reference evapotranspiration.

Assessing landslide susceptibility with a GIS using qualitative and quantitative methods in Knox county, Nebraska - Christian Cruz

  • Thesis Defense
  • 4/14/2017

A landslide susceptibility map was developed for Knox County, Nebraska, located along the Missouri River valley. The Missouri River valley has significant changes in relief, gradually receding into rolling loess hills further to the south and southeast of the county. This thesis is designed to assess landslide susceptibility using a DEM derived from LiDAR, land cover, and soil series. Data were assessed using a quantitative approach using logistic regression within Rstudio and a geographic information system (GIS). Based on the quantitative results, factors were qualitatively assigned landslide potential values. The six factors used in determining the area's susceptibility to landslides, were parent material, soil series, land cover, slope degree, slope curvature, and slope aspect. Previous investigations in the region indicate the Cretaceous shale parent material is a major contributing factor in landslide development. Physical map units were acquired to differentiate the soil type and parent material. DEMs derived from LiDAR were analyzed in GIS to provide slope degree, curvature, and aspect information. Logistic regression data was extracted from randomly selected points along landslide scarps. All six factors were reclassified by their odds ratios and the combination of factors was applied to produce a resultant map to show landslide susceptibility. The resultant map of Knox County locates and distinguishes areas that are more likely to incur landslide activity or areas that have already experienced a significant amount of landslides.

Causes of variation in fine-scale pheasant hunter habitat use - Lyndsie Wszola

  • Thesis Defense
  • 4/14/2017

Variation in hunter behavior within regulatory parameters has the potential to influence prey populations in evolutionary time by imposing selection and in ecological time by inducing changes in prey habitat use. When prey leave managed lands in response to hunting, the change in prey distribution may be suboptimal to both hunters and prey. To understand how hunting activity influences prey spatial decisions, we must first understand how hunting pressure becomes distributed in time and space. We assessed how transportation infrastructure, physical stress, variation in vegetation structure, land use on adjacent fields, and fine-scale pheasant distribution influenced hunter movement through public access hunting fields in southwest Nebraska. We found that hunter space use increased with increasing pheasant density and decreased with increasing distance from roads and public access hunting signs. Our results corroborate at a finer scale landscape studies of hunter movement suggesting that hunters are influenced by the distribution of infrastructure and prey. Our results further imply that conservation practitioners may be able to subtly manage fine-scale hunter behavior through the strategic placement of access infrastructure.

Recreational Angler Behavior and Site Choice within Midwestern Reservoirs - Brian Harmon

  • Thesis Defense
  • 4/12/2017

Recreational anglers are influential predators in inland fisheries that act across multiple scales to complete a fishing trip. Although between-trip and across-waterbody angler behavior and site choice are well documented, within-trip behavior is poorly understood. Recreational fisheries are complex systems, in which interactions occur across scales.

I tested the connections between angler behavior, trip outcome, and angler perceptions to elucidate within-trip angler behavior. I recorded angler site choice across the open-water season at four Salt Valley reservoirs and compared angler location to a suite of habitat variables. I used a competing-models approach to determine what model of physical features best determined angler choice. I compared realized choice results (where I recorded anglers) with stated preferences (what anglers said was most important for site choice). Results are intended to increase understanding of angler behavior for effective fisheries management.

Influences of catch-and-release angling on fish behavior - Alexis Fedele

  • Thesis Defense
  • 4/6/2017

Complex interactions exist between ecological and sociological systems but can be difficult to assess. Newly opened recreational fisheries provide the opportunity to explore direct social effects on naive (i.e., previously unexploited by anglers) population of fish. We examine the influence of angling on wild fish populations, and aim to identify the behavioral outcomes in fish resulting from angling through laboratory experiments. We assessed the short-term (30-d) response of fish populations to recreational angling at two newly opened reservoirs in Nebraska. At one reservoir, we noted declining catch rates in catch-and-release-regulated fish but not in harvest-regulated fish. We hypothesized that caught-and-released fish were given the opportunity to alter behavior, whereas harvested fish were presumably removed from the waterbody after capture with no opportunity to alter behavior. However, this was not observed in both reservoirs, thus further investigation was warranted into the ability of fish to alter behavior to avoid recapture in a controlled environment. In the laboratory, we evaluated whether behavioral types (i.e., bold and shy) in fish affect the ability to learn to avoid subsequent recapture. We observed that both shy and bold individuals had a decreased probability of capture over the seven-day experiment. Bolder individuals exhibited a greater probability of capture across gear types (control, hook, lure) compared to shyer individuals. Ration level appeared to have little influence on the probability of capture. Fish exposed to lures exhibited lower probability of capture than the hook and sham hook treatments across behavioral types. The learned avoidance of capture has strong implications for fishing-induced evolution, efficacy of management regulations, and satisfaction of anglers.

Problematizing socio-scientific issues: An approach to understanding student decision-making using construal level theory - McKinzie Peterson

  • Thesis Defense
  • 3/28/2017

Science literacy refers to the ability to understand and utilize scientific information for personal and societal level decisions. A common recommendation by scientists is to use socio-scientific issues (SSIs) to develop and improve science literacy. Students need structured frameworks to help them learn to navigate and address SSIs. An important step in these frameworks is the problem definition, which can significantly influence solutions proposed by students and their ultimate decisions. Construal Level Theory (CLT), which is a theory that describes the relationship between psychological distance and the extent of abstract and concrete thinking, is one way in which problem definitions can differ. Several studies in CLT suggest differences in how abstract or concrete situations are portrayed to students can significantly change their decisions, perceptions, and use of personal values.

This study explores how CLT is related to decisions and perceptions of 6thgraders (n = 116) on a wind energy SSI and the use of values in decision-making on an undergraduate (n = 73) prairie dog SSI. Mixed/neutral perceptions of wind turbines in the 6thgrade population had higher abstraction scores than those with negative perceptions. In the undergraduate prairie dog study, abstraction is related to values students utilized in their problem statements and criteria during the decision-making process. Teaching implications for this research are discussed.

Heterogeneity of avian breeding habitat on private lands of the Northern Great Plains - Maggi Sliwinski

  • Dissertation Defense
  • 2/17/2017

Most intact rangelands in North America are privately owned and used for beef production. Vegetation heterogeneity is an important habitat component for maintaining biodiversity, but private land may be more homogenous than desired. My research had two major components: 1) to examine whether a variety of grazing strategies created vegetation heterogeneity in a large, intact rangeland, and 2) to understand beef producers' attitudes about vegetation heterogeneity.

First, I sampled vegetation structure, composition, and bird abundance in Cherry County, Nebraska. I examined the relationship of vegetation heterogeneity and bird abundance and communities to management variables. Grazing strategy had few relationships to vegetation structure or bird abundance and communities, but pasture-level management variables were relatively important. Multiple grazing strategies on a landscape did not contribute to vegetation heterogeneity, and vegetation structure and bird communities were more homogenous than expected. Federal land could be used to ensure that heterogeneity exists on the landscape for species that cannot find suitable habitat on private land.

Second, I interviewed 12 beef producers to explore their opinions of heterogeneity, and conducted a mail survey of producers in Nebraska, South Dakota, and North Dakota. Both indicated that beef producers' main concern is sustainable beef production, and this likely contributes to homogenizing the rangeland landscape. My data confirm that producers appreciated wildlife and have positive views toward landscape management. Although fire and prairie dogs might enhance heterogeneity of vegetation, these were negatively viewed because they increased risk to the producer. Producers' responses provided insights on how conservationists should engage them to manage for biodiversity. I recommend engaging producers through Extension educators and hands-on activities.

Causes and Consequences of Landcover Change in Landscapes of Nebraska, USA - Dan Uden

  • Dissertation Defense
  • 1/27/2017

Landcover change is an important global change process with diverse direct and indirect causes and consequences within social-ecological systems. Although substantial uncertainties exist regarding the future of landcover change and its affects, the consideration of past, present, and potential future changes could be useful for learning, assessing, adjusting, and preparing.

I consider case studies of past, present, and future landcover and landcover change in selected landscapes of Nebraska, U.S.A. Specifically, I present species distribution model ensembles for 16 tree species in the Missouri River bluffs of extreme southeast Nebraska, assess functional connectivity of wetland habitats in three central Nebraska landscapes that have experienced varying degrees of human-driven landcover change over the past several centuries, and develop scenario storylines and simulations of future landcover change for the Pine Ridge of extreme northwest Nebraska. Results are useful for increasing understanding about regional landcover changes and for informing ongoing conservation activities.

Integration of Hydrogeophysical Datasets for Improved Water Resource Management in Irrigated Systems - Catie Finkenbiner

  • Thesis Defense
  • 1/7/2017

Water scarcity is predicted to be the major limitation to increasing agronomic outputs to meet future food and fiber demands. With the agricultural sector accounting for 80-90% of all consumptive water use and an average water use efficiency (WUE) of less than 45%, major advances must be made in irrigation water management. Precision agriculture offers the technologies to address and manage for infield variability and incorporate that variability into management decisions. The major limitation to implementing this technology often lies in the management of spatial datasets and the writing of irrigation prescription maps that address variables impacting crop yield and soil moisture. While certain datasets and mapping technologies exist in practice, here I explored the utility of the recently developed cosmic-ray neutron probe (CRNP) which measures soil water content (SWC). The key advantages of CRNPs are the sensor is passive, non-invasive, mobile and soil temperature invariant making data collection more compatible with existing farm operations and extending the mapping period. The objectives of this study were to investigate strategies to: 1) improve the delineation of management zones within a field and 2) estimate spatial soil hydraulic properties (field capacity and wilting point) to make effective irrigation prescriptions. To accomplish this, a series of CRNP SWC surveys were collected in a 53-ha field near Sutherland, Nebraska. The SWC surveys were analyzed using Empirical Orthogonal Functions (EOF) to isolate the underlying spatial structure. I found that measured SWC at field capacity and wilting point were better correlated to CRNP SWC EOF as compared to other commonly used datasets. Based on this work I proposed a sampling strategy for better qualifying soil hydraulic properties. While the proposed strategy will increase overall effort as compared to traditional techniques, rising scrutiny for agricultural water-use may make this technology cost effective.

Longitudinal Flow Variability and Population Characteristics of Large-River Fishes: Importance of Scale in Large-River Ecology - Jonathan Spurgeon

  • Dissertation Defense
  • 11/30/2016

Many large-river fish populations have experienced dramatic declines as a result of anthropogenic alteration of river systems. The natural flow regime which is comprised of the magnitude, timing, duration, rate-of-change, and frequency of seasonal flows is often compromised following anthropogenic alteration of river systems. Alteration of the natural flow regime has been linked to changes in many ecological processes including food resource availability and fish growth. Therefore, quantifying the influence of flows on fish populations is a critical piece of information needed for proper conservation and management. Additionally, information regarding fish population structure across river systems is often limited. Conservation and management strategies need information regarding the presence of isolated populations or if populations are maintained through some form of meta-population connectivity. Insight to both fish response to changing flow patterns and population structure across a riverscape are likely dependent on temporal and spatial scales of observation. In this dissertation, I use hydrological data from in situ gauging stations to describe the spatial and temporal presence of unique flow patterns along the Platte River, NE, USA. I use growth information for channel catfish Ictalurus punctatus to assess changes in growth with respect to the components of the Platte River flow regime. I also assess population structure of channel catfish and shovelnose sturgeon Scaphirhynchus platorynchus across mainstem and tributary environments using a combination of otolith microchemistry and mark-recapture.

Exploration of Student Biodiversity Knowledge and Decision-making for a Wildlife Conservation Socioscientific Issue - Ashley Alred

  • Thesis Defense
  • 11/16/2016

Global biodiversity, a foundation for ecosystem function, is diminishing at a rate unprecedented in the last 50 years. Biodiversity loss and ecosystem services deterioration is linked to increased food insecurity, reduced water quality and availability, decreased energy security, higher economic losses and human suffering, and damaged social relations (Millennium Ecosystem Assessment, 2005). Consequently, educational strategies should support students in their development of ecological understanding and formal decision-making skills so they are equipped with meaningful tools they can one day use as scientifically literate citizens. To contribute to that mission, this study seeks to better understand student 1) comprehension and explanation of biodiversity concepts and 2) decision-making in the face of a conservation-related socioscientific issue.

Past research shows that students at all levels of education have difficulty explaining genetic variability, which is a key concept underlying biodiversity, natural selection, and species conservation. The first part of our study explores middle school, high school, and undergraduate student understanding of genetic variability in the context of a captive breeding program for wildlife conservation. Results from this study show that several alternative conceptions of genetic variability persist across all grade levels.

The second part of our study explores how undergraduate students make decisions in unstructured and structured decision-making settings when posed with a question relating to mountain lion conservation in Nebraska. Some variables (e.g., value orientations, demographic information, or ecological content knowledge) are predictive of students' management decisions depending on the context in which the question was asked. Findings suggest that student decision-making may be more closely linked to students' value orientations, social identity and conservation knowledge than to students' own stated objectives and evaluation criteria related to mountain lion hunting. This study also suggests that implementing a structured decision-making framework in the classroom can be an effective tool to help support students' examination of value tradeoffs among options for solving complex problems. I provide teaching implications for using these tools in supporting students to make formal, holistic decisions for complex socioscientific issues that transfer to real-world contexts.

College and University Sustainability Officers' Experiences with Green Office Programs: A Qualitative Investigation - Logan Lamb

  • Thesis Defense
  • 11/11/2016

The number of sustainability programs in higher education continues to increase. Green office programs have become a cornerstone of sustainability programming on college and university campuses across the country. This exploratory qualitative study involved college and university sustainability officers and investigates their experiences changing behaviors through green office programs. The goal of this study was to provide insight into green office programs. Two side-by- side studies were conducted to provide a detailed analysis of green office programs at both small and large institutions of higher education. Eleven major themes emerged from the study. Six themes emerged from the qualitative analysis of sustainability officer's experiences promoting green office programs in large schools. Five themes and two sub-themes emerged from the qualitative analysis of sustainability officer's experiences promoting environmental behaviors in small schools. One theme, education provided through the institution's sustainability office was held in common between the two populations; however, there were some differences in educational programming. This study provides the foundation for further research into green office programs and other sustainability programs in higher education.

What can an agroclimatologist do for the Midwestern corn community? - Shuwei Dai

  • Dissertation Defense
  • 11/10/2016

In the Midwest U.S., weather is a major driving force of the success or failure of corn production industry. The agricultural community often have to face challenges relative to climate variability and climate change. However, there is a big difference between the scientists' views and the Midwestern corn stakeholders' perspectives when it comes to climate science. Hence, it is critically important for an agroclimatologist to isolate useful climate data and interpret these data in usable ways to help the corn community better understand the scientific information and ultimately use the information in the agricultural decision making process. By aiming to serve the Midwestern corn community, my dissertation study focuses on three questions:

  1. In the Midwest: How have temperature and precipitation changed during the growing season for corn since 1980? (http://www.hprcc.unl.edu/climatetrends.php)
  2. In Nebraska: What is the best method to estimate thermal time for corn when temperature data are limited to a daily timescale?
  3. At Mead, NE: What are the historical effects of temperature and precipitation on corn yield under irrigated and rainfed conditions?

In the long run, these efforts will assist the agricultural community in striving to make more sustainable farming operations and lead to greater resilience to the faster changing climate in the Midwest.

River Otter (Lontra Canadensis) Distribution and Habitat Suitability in Nebraska - Nathan Bieber

  • Thesis Defense
  • 9/26/2016

After nearly a century of absence in Nebraska, the Nebraska Game and Parks Commission (NGPC) began releasing otters at seven release sites in 1986. The species was listed as a Tier-1 At Risk species at that time. Early indications are that the river otter population in Nebraska is thriving, and NGPC is now in the process of evaluating a de-listing plan. In order to proceed with de-listing, more information on otter distribution in the state is needed.

Over the course of two field seasons, I gathered presence and absence sign data (scat, tracks, etc.) for otters on Nebraska's navigable rivers. In addition, I obtained a dataset comprised of 37 years of incidental trapping reports and biologist sightings from NGPC. Occupancy and maxent modeling techniques were used estimate otter distribution throughout the state and how habitat factors influenced their distribution.

Distribution estimates were consistent with estimates produced by NGPC with otters being most likely to occupy the Platte River, the southern Loup River system, the northern Elkhorn River, and sections of the Niobrara River. The distance to a release site was the strongest predictor of otter presence followed by river flow rate and beaver presence. These findings will be used to inform de-listing efforts and management efforts in the future.

Population Characteristics, Population Estimate, and Habitat Associations of Shovelnose Sturgeon in the Lower Platte River - Jeremy Hammen

  • Dissertation Defense
  • 9/19/2016

The Convention of International Trade of Endangered Species of Wild Fauna and Flora (CITES) listed every member of the Acipenseridae family as either an Appendix I or Appendix II protected species, resulting in regulation of any commercial trade by the provisions of CITES. Shovelnose Sturgeon are among this listing. Declines in populations throughout their range (Mississippi and Missouri River Basins) have taken place over the past few decades. These declines in populations have made it crucial to better understand the life-history characteristics of Shovelnose Sturgeon. This dissertation provides insight on the population patterns of a Shovelnose Sturgeon population in the lower Platte River, Nebraska, and helps fill gaps in information needed to make appropriate management decisions for Shovelnose Sturgeon.

Adaptation to Climate Change via Insurance and Financial Incentives - Eric Holley

  • Thesis Defense
  • 7/25/2016

Catastrophic climatic events have accounted for 72% of global insurance claims and totaled ~$1 trillion from 1980 to 2012. Government policies to reduce systemic risk have been the predominant approach for multi-level mitigation and adaptation to climate change. The analysis presented here shows how forceful and effective market-based approaches for adaptation and mitigation to climate change already operate via the insurance industry. Feedbacks from insurance to society include these primary changes: 1) premiums and insurance policies, 2) non-coverage, and 3) policy making and litigation. Through these mechanisms, the insurance industry actively manages climate change adaptations and creates incentives to lessen impacts on industry and society. For mitigation of climate change, renewable energy-based energy production has become more of a priority for utilities in recent years. However, renewable energy is competitively disadvantaged compared to fossil-fuel based systems due to high investment costs, the intermittent nature of renewables, and a lack of pricing for externalities. A model is used for calculating the total cost of a renewable utility and the cost of energy for that utility. Three scenarios were modeled to show the effects of incentives on the cost of production to the utility and the costs to the incentive providers. In Nebraska, the incentive was found to provide some relief to the utility compared to the null scenario and the federal incentive provided significantly more relief to the utility. Costs for the incentive investor with the federal incentive were significantly higher than with the Nebraska incentive, compared to the null scenario. To develop renewable-energy production and mitigate climate change impacts, incentives enable market entry where externalities for fossil fuels are not adequately priced. Adaptation to climate change requires thorough understanding of how the impacts affect society and how society might mitigate and adapt to the impacts of climate change.

Applications of Time-Lapse Imagery to Capture and Communicate Ecological Dynamics of a Water-Stressed System - Emma Brinley Buckley

  • Thesis Defense
  • 7/20/2016

TO EFFECTIVELY MANAGE OUR NATURAL RESOURCES, IT IS NECESSARY TO OBSERVE AND DOCUMENT ECOSYSTEM DYNAMICS, AS WELL AS COMMUNICATE ECOLOGICAL CHANGE TO PUBLIC AUDIENCES. TIME-LAPSE IMAGERY IS A VALUABLE TOOL TO CAPTURE AND DEPICT NATURAL SYSTEMS. I SOUGHT TO ENHANCE OUR UNDERSTANDING OF A WATER-STRESSED SYSTEM BY ANALYZING IMAGERY, IN ADDITION TO INTEGRATING IMAGES WITH DATA VISUALIZATION TO ILLUSTRATE THE COMPLEXITY OF A RIVER BASIN IN CENTRAL NEBRASKA. IMAGE ANALYSIS WAS USED TO QUANTIFY WETLAND WATER INUNDATION AND VEGETATION PHENOLOGY. THESE MEASUREMENTS WERE COMBINED WITH OTHER PASSIVE MONITORING METHODS TO EXAMINE THE RELATIONSHIP BETWEEN VEGETATION PHENOLOGY AND BAT ACTIVITY, AS WELL AS WETLAND INUNDATION AND WATER QUALITY. MOREOVER, TIME-LAPSE DATA SEQUENCES WERE CONSTRUCTED BY INTEGRATING TIME-LAPSE IMAGERY WITH DATA VISUALIZATION IN AN INTERACTIVE DIGITAL FRAMEWORK TO EXAMINE THE APPLICATIONS FOR COMMUNICATING SOCIAL-ECOLOGICAL DYNAMICS. FINDINGS SUGGEST VEGETATION PHENOLOGY WAS DIFFERENTIALLY ASSOCIATED WITH SEASONAL BAT ACTIVITY, POSSIBLY RELATED TO MIGRATORY VERSUS RESIDENT LIFE HISTORY STRATEGIES. RESULTS OF EXAMINING WETLAND HYDROLOGY INDICATED A TIME LAG IN WETLAND INUNDATION WHEN COMPARED TO STREAMFLOW IN THE RIVER AND INUNDATION WAS FOUND TO BE CORRELATED WITH NITRATE, DISSOLVED OXYGEN, AND DEA, AND NEGATIVELY CORRELATED WITH WATER TEMPERATURE. IN EXAMINING COMMUNICATIVE APPLICATIONS, TIME-LAPSE DATA SEQUENCES DEMONSTRATED THE ABILITY TO DEPICT VARIOUS ECOLOGICAL DYNAMICS WITHIN A TANGIBLE CONTEXT THAT ARE OFTEN TOO SUBTLE TO SEE OR BEYOND THE TEMPORAL SCALE OF UNAIDED HUMAN OBSERVATION. OVERALL, THESE FINDINGS INDICATE THE DUAL UTILITY OF TIME-LAPSE IMAGERY TO ACQUIRE DATA AND ILLUSTRATE ECOLOGICAL DYNAMICS.

Instructional Framing and Student Learning of Community Interactions - Nathaniel Niosco

  • Thesis Defense
  • 7/18/2016

To understand the complex systems and concepts of ecology requires a foundation of knowledge that students often gain in the classroom. The purpose of this research was twofold. First, I wanted to understand the differences between students who used surface reasoning skills and students who used deep reasoning skills to develop the foundational knowledge of community interactions. Second, I wanted to understand how two types of instructional framing may affect students’ ability to apply knowledge between multiple contexts.

In the first study, undergraduate introductory biology students were given pre-instruction and post-instruction assessments that tested their ability to explain the effects of disturbances within a food web. Findings from this study suggest that when learning a new subject, students use a combination of surface and deep reasoning to solve problems and surface reasoning students have the potential to meet or exceed the same standards as deep reasoning students. In the second study, students were taught food web concepts and reasoning skills using either bounded framing or expansive framing methods. Expansive framing is an instructional method designed to help students understand that the concepts and skills taught in a single context are applicable in multiple scenarios. In a follow-up session, students were asked questions about the knowledge gained from the prior session and asked to reason about the effects of food web perturbations. Findings from the second study suggest that compared to bounded framing, expansive framing does not significantly affect the transfer of reasoning skills between contexts. The findings also suggest that students transferred some reasoning skills from the first session and applied the skills to the second session when prompted to reason about disturbances in a food web.

The Influence of Training on Guides and Their Environmentally Responsible Behaviors and Transformational Leadership Abilities - Qwynne Lackey

  • Thesis Defense
  • 7/12/2016

The ecotourism and interpretive fields were established, in part, to protect natural environments. This goal is achieved by implementing environmentally responsible practices and by providing transformative experiences for visitors. Previous research suggests that ecotour and interpretive guides play a vital role in implementing environmentally responsible behaviors (ERBs) and creating transformative visitor experiences. Other researchers have found that guide training yields many benefits for guides and their abilities. The purpose of this research was to explore the influence of established training programs on guides and their ERBs and transformational leadership abilities using qualitative methods, including participant observation and interviews, and quantitative survey methods. Case studies were performed on populations affiliated with two training providers: EcoTraining, a guide training program based in South African, and a National Association for Interpretation. In both cases, a statistically significant relationship was found between students' self-reported guiding competency scores and transformational leadership abilities. The majority of students surveyed in each case also self-reported practicing the majority of measured ERBs, but the qualitative data shows that students' ERBs are influenced by training only if certain emphases and activities are included. The findings also highlight the importance incorporating role modeling, experiential learning activities, and instructors who exhibit transformational leadership characteristics. Structured and unstructured time in nature and alone time are also important to include, as it allows students to recover from mental fatigue and engage in the self-reflection necessary to grow as an individual and develop connection to nature. Though training does increase guides’ ability to lead transformative experiences, interview data shows that guides' abilities and behaviors are also influenced by factors outside of training, such as visitors, other guides, and managers.

An Investigation into Factors Influencing Attitudes toward a Wildlife Corridor - Erin Kubicek

  • Thesis Defense
  • 7/11/2016

Habitat fragmentation poses a serious threat to biodiversity in eastern Nebraska. Today, over 98% of Nebraska’s tall-grass prairie has been lost and what remains exists mostly as remnants less than 80 acres in size. The Prairie Corridor on Haines Branch will be one of the first man-made wildlife corridors in eastern Nebraska with expansion of prairie habitat as one of its main goals. The purpose of this study is to explore the potential relationship between attitudes toward wildlife corridors, connection to nature, environmental values and norms, providing some insight into the general willingness (or lack thereof) to support conservation-related programs such as wildlife corridors. Park visitors and residents currently living near an existing wildlife corridor were asked to complete a survey measuring attitudes, connection to nature, environmental values, and norms. In total, 152 park visitors and 272 residents completed the survey. Overall, park visitors had significantly higher attitudes toward wildlife corridors than did residents. In addition, Pearson product-moment correlation coefficients showed that connection to nature and attitude toward a wildlife corridor were significantly correlated. Altruistic values, biospheric values, and personal and social norms were also significantly correlated with attitudes toward wildlife corridors. Regression analysis was used to test if connection to nature, personal norms, social norms, descriptive norms, egoistic environmental values, altruistic environmental values, and biospheric environmental values significantly predict attitudes toward a wildlife corridor for all participants. The results of the regression analysis indicated the ten predictors explained 41.4% of the variance. It was found that personal norms significantly predicted attitudes toward a wildlife corridor, as did biospheric environmental values.

Industrial Ecology Analysis of the Potential for an Eastern Nebraska Industrial Symbiosis Network (ENISN): A Comparative Study - Brad Behne

  • Thesis Defense
  • 5/17/2016

The area of Eastern Nebraska north of Omaha, including the municipality of Blair is host to a collection of unique companies and industries. These industries, driven by the agricultural and urban economy of the area, as well as the geographic proximity to each other, provide an opportunity to study the potential for a network where individual entities utilize the concept of industrial symbiosis. This potential network is referred to as the Eastern Nebraska Industrial Symbiosis Network (ENISN). Industrial symbiosis, a sub-set of industrial ecology, engages separate industries in a collaborative and collective approach to the flow of materials, energy, water, and/or by-products between each other. The outcome of industrial symbiosis is advantageous to not only the companies, but to the environment as well. The incorporation of ecological economic principles are at the core of industrial symbiosis. A "circular-economy" invites a more sustainable approach to the efficient allocation of resources and a philosophy of an end to growth, and drive this unique economy that differs from the traditional neoclassical approach to resource allocation.

This study compared the potential of an ENISN with the existing Kalundborg Symbiosis in Kalundborg, Denmark, a long established example of industrial ecology and the use of an eco-industrial network where the by-product of one enterprise is used as a resource by another enterprise in a closed cycle. The results of this study provide evidence that the ENISN study site has enough indicators for the potential of an industrial symbiosis site. Based on analysis of material flows and inductive themes derived from interviews with potential partners, sufficient collaboration and environmental stewardship exist in the study area. The results of the study also suggest that the human capital exists to make an ENISN; however, the impetus to take on the challenging ontological barriers remains to be seen.

The Cosmic-ray Neutron Probe Method for Estimating Field Scale Soil Water Content: Advances and Applications - William Avery

  • Thesis Defense
  • 5/13/2016

The need for accurate, real-time, reliable, and multi-scale soil water content (SWC) monitoring is critical for a multitude of scientific disciplines trying to understand and predict the earth's terrestrial energy, water, and nutrient cycles. One promising technique to help meet this demand is fixed and roving cosmic-ray neutron probes (CRNP). However, the relationship between observed low-energy neutrons and SWC is affected by local soil and vegetation calibration parameters. This effect may be accounted for by a calibrated equation based on local soil type and the amount of standing biomass. However, determining the calibration parameters for this equation is labor and time intensive, thus limiting the full potential of the roving CRNP in large surveys and long transects, or its use in novel environments. In this work, our objective is to develop and test the accuracy of using globally available datasets (clay weight percent, soil bulk density, and soil organic carbon) to support the operability of the CRNP. Here, we develop a 1 km product of soil lattice water over the CONtinental United States (CONUS) using a database of in-situ calibration samples and globally available soil taxonomy and soil texture data. We then test the accuracy of the global dataset in the CONUS using comparisons of 61 in-situ samples of clay percent (RMSE = 5.45 wt. %, R2 = 0.68), soil bulk density (RMSE = 0.173 g/cm3, R2 = 0.203), and soil organic carbon (RMSE = 1.47 wt. %, R2 = 0.175). In addition, we conduct an uncertainty analysis of the global soil calibration parameters using a Monte Carlo error propagation analysis (maximum RSME ~0.035 cm3/cm3 at a SWC = 0.40 cm3/cm3). Fast growing crops (i.e. maize and soybeans) contribute to the CRNP signal primarily through the water within their biomass and this signal must be minimized for soil moisture retrieval. This was done by using a vegetation index derived from MODIS imagery as a proxy for standing wet biomass (RMSE < 1 kg/m2). Lastly, we make recommendations to the design and validation of future roving CRNP experiments.

Essays on Decision Support for Drought Migitgation Planning: A Tale of Three Tools - Mark Svoboda

  • Dissertation Defense
  • 4/18/2016

The fact that droughts cover all scales, both temporally and spatially, requires an approach that is diverse and flexible. Just as there is no one definition of drought, there is no one prescribed way of planning or monitoring drought. Optimally, the best strategy calls for a multi-pronged approach aimed at dealing with droughts well in advance of their onset. The basic premise of a drought risk management approach is to plan and prepare for droughts given they are a normal part of most climate regimes and regions around the world. Such an approach is much preferred to a reactive, crisis-based approach that only deals with drought after the fact.

The foundation of a drought plan can be thought of as consisting of three "pillars": drought monitoring and early warning, impacts and vulnerability/risk assessment and planning. This dissertation is separated into three papers that address portions of all of these pillars.

The first is the development of an evaluation method to analyze and grade state drought planning efforts in the United States. The second paper focuses on the development of a Drought Ready Communities program aimed at developing a guide and resource for drought risk management at the community scale. Finally, understanding one's drought history, or climatology, is essential toward helping better understand where and when droughts and subsequent impacts have occurred, allowing for both the anticipation of what impacts may occur when droughts of various magnitudes return as well as serving as a preparation tool for the reduction or risk from a decision support role in drought mitigation planning. Knowing the frequency and magnitude (a function of severity and duration) of various degrees should be an essential part of the planning process.

These three papers and concepts are meant to work not only as stand-alone decision support tools, but also together as part of an overarching umbrella of drought mitigation strategies.

Distinguishing Calliphorid Puparia through Application of Confocal Laser Scanning Microscopy - Christian Elowsky

  • Dissertation Defense
  • 4/18/2016

n/a

Assessment of Resource Use and Landscape Risk for African Lions (Panthera leo) in Eastern Botswana - Andrei Snyman

  • Dissertation Defense
  • 4/15/2016

African lion (Panthera leo) populations have been severely affected in recent decades through increasing habitat loss, depletion of natural prey, poaching and unsustainable levels of trophy hunting, with an estimated 20,000 - 30,000 free-ranging lions left in Africa and range contraction of over 75%. In southern Africa, many small populations have been fenced in an attempt to allow lions to persist in a human dominated landscape yet populations within protected areas are, however, still exposed to legal and illegal hunting, road kills, poisoning and snaring. These human-induced mortalities affect lion populations in various ways, further compromising their viability and likelihood of survival. My study investigates the effects of anthropogenic factors on a lion population found in Eastern Botswana. By means of Resource Utilization Functions (RUF's) lion habitat space use is quantified in an attempt to predict and identify viable lion corridors through to which we use Circuit Theory modeling.

Simple, Novel Approaches to Investigating Biophysical Characteristics of Individual Mid-latitude Deciduous Trees - Humphrey Kalibo

  • Dissertation Defense
  • 4/15/2016

Forests play a critical role in the functioning of the biosphere and support the livelihoods of millions of people. With increasing anthropogenic influences and looming effects associated with climatic variability, it is crucial that the research community and policy makers take advantage of the capabilities afforded by remote sensing technologies to generate reliable and timely data to support management decisions. Set in the species-rich woodland of Prairie Pines in Lincoln, Nebraska, this research addresses three distinct objectives that could contribute towards forest research and management. First, three supervised classification algorithms were applied to two hyperspectral AISA-Eagle images to evaluate the capability for spectrally identifying selected tree species. The findings show that each algorithm had low to moderate overall classification accuracies (46%-62%), probably due to mixed pixels resulting from pronounced heterogeneity in tree diversity; however, the algorithms could be a rapid means to assess species composition. The second objective is an investigation into how twelve individual morphologically different deciduous trees transmit incoming photosynthetically active radiation (PAR) over the course of the growing season. It was found that more diffuse light was transmitted than direct light, dictated by seasonality, vegetation fraction (VF), and leaf size. In the final objective, VF derived from upward-looking hemispherical photographs of twelve deciduous tree canopies and eight spectral vegetation indices (VIs) calculated from in situ single leaf-level reflectance data were used to investigate whether the VIs could mimic and estimate the temporal patterns of measured VF of each tree over the growing season. The findings show that all the indices accurately depicted the temporal patterns of the photo-derived VF. NDVI and SAVI had the highest correlations (R2 > 0.7; RMSE < 20%; d > 0.7; E > 0.8) and closely mirrored the temporal patterns of VF for nine of the twelve trees, while SR worked well for low-foliage trees. The amount of foliage cover affected the accuracy with which the VIs estimated the VF of the various trees. Overall, this study has suggested a simple methodology that combines two distinct sets of data of different spatial scales to examine a vegetation biophysical parameter over a growing season. The findings provide preliminary insights into how individual mid-latitude deciduous trees partition incoming solar radiation at each phenological stage and over the growing season. The research should stimulate more robust inquiry into the use of both remote and in situ sensing tools in the study of vegetation biophysical parameters.

Improved Microplate-scale Fluorometric Soil Enzyme Assay to Detect β-Glucosidase Activity in Agricultural Management Practices - Emily Hoehn

  • Thesis Defense
  • 4/15/2016

Soil extracellular enzymes are sensitive to changes in soil organic matter, soil physical properties and microbial activity, and can be used as indicators of soil quality. Enzymes chosen as indicators of soil quality must be easily quantified and reflect changes in ecosystem and anthropogenic activity. β-glucosidase, a well documented enzyme responsible for the degradation of cellulose and release of glucose in the soil environment is an important indicator of soil organic nutrient cycling. This research focuses on development of a microplate-scale fluorometric assay for fast, high throughput monitoring of β-glucosidase activity as a measure of soil quality. Application of this newly developed assay to soil samples from a no-till management system show clear differences due to cropping rotation and nitrogen management. Improved methods for measuring soil enzymes can ultimately provide valuable information on microbial community activity, soil quality and ecosystem productivity.

Dating Late Quaternary Alluvial Fills in the Platte River Valley using Optically Stimulated Luminescence Dating - Jake Bruihler

  • Thesis Defense
  • 4/13/2016

Underlying the Platte River Valley in Nebraska, alluvial fills record the geologic history of the Platte River in the late Quaternary. Sediment cores were recovered from these alluvial deposits in rough transects along the Platte River floodplain near the towns of North Platte and Kearney, Nebraska. Optically Stimulated Luminescence (OSL) dating was used to determine burial age of recovered sediments, and to quantify the thicknesses of Pleistocene and Holocene age alluvial fill in the two study areas. OSL ages were calculated using the single aliquot regenerative procedure on quartz sand grains. Based on results from OSL dating, burial ages ranged from approximately 1 to 68 ka. Holocene age alluvium in both study sites is present to depths of up to 8 meters below the present floodplain. Late Pleistocene age sediment that can be dated with OSL is found at depths of up to 15 m below the present floodplain. Our geochronology indicates there are considerable differences in age with depth at the two study sites. Evidence suggests that both study sites experienced aggradation in the late Pleistocene, followed by entrenchment of the alluvial fills during the late Holocene.

Exploring parasitism in antiquity through the analysis of coprolites and quids from La Cueva de los Muertos Chiquitos, Rio Zape, Durango, Mexico - Johnica Morrow (Fetsch)

  • Dissertation Defense
  • 4/1/2016

Coprolites excavated from La Cueva de lost Muertos Chiquitos (CMC) were examined for evidence of parasitism utilizing both standard coprolite processing procedures and molecular techniques. A total of 100 coprolites were processed for microfossil examination via light microscopy. These coprolites contained the eggs of seven different types of parasitic helminths (Echinostoma, Enterobius, Physaloptera, Taenia, Toxascaris, and Trichuris). These included members of three different taxonomic classes, Cestoda, Trematoda, and Nematoda, representing two taxonomic phyla, Platyhelminthes and Nemata. Of the coprolites, 90 were deemed suitable for enzyme-linked immunosorbent assay (ELISA) analysis. A gram of each coprolite was extracted for analysis and tested for the presence of coproantigens specific to three diarrhea-inducing protozoan parasite, Entamoeba histolytica, Giardia duodenalis, and Cryptosporidium parvum. All coprolites tested negative for E. histolytica and G. duodenalis, however, 73% of coprolites tested positive or likely positive for C. parvum. A total of 45 quids were also examined using ELISA analysis to test for human-produced antibodies made in response to Toxoplasma gondii and Trypanosoma cruzi infections. Though no such antibodies were detected, additional testing of quids from this site suggest that taphonomic issues related to the recovery of human antibodies from archaeological materials likely played a role. The potential for future archaeoparasitological studies utilizing quids as source materials is discussed. The pathoecology of CMC is discussed in light of the new parasite data presented herein.

Use of camera traps to estimate population density and abundance of ungulate population: A case study on Gaur (Indian bison) - Ree Tanasarnpaiboon

  • Dissertation Defense
  • 3/31/2016

Gaur, a wild cattle, is ditributed only in South Asia through South East Asia. They are one of the tiger's prey species and habitat architect. Population status in most subpopulation across their ranges is still unknown. Conventional survey methods for gaur surveys are rapid assessment approaches, such as transect surveys and distance sampling. However, use of camera traps in wildlife studies is widespread. I utilize information from camera trapping to estimate abundance and density of gaur in Kuiburi National Park, Thailand. Validation of study design and modelling of camera trap based surveys will provide alternative approaches to monitoring gaur and other ungulates.

Occupancy Analysis and Density Estimation of Kori Bustards (Ardeotis kori) and Helmeted Guineafowl (Numida meleagris) for Use in Landscape Conservation Planning in the Northern Tuli Game Reserve, Botswana - Katie McCollum

  • Thesis Defense
  • 12/1/2015

The utilization of occupancy and abundance analyses for understudied species can lead to more informed conservation planning and decision-making on both the local and landscape levels. Here, we focus on two charismatic bird species native to eastern Botswana, kori bustards (Ardeotis kori) and helmeted guineafowl (Numida meleagris). We performed distance sampling for both species over two field seasons throughout the Northern Tuli Game Reserve, Botswana during June-July 2014 and May-July 2015. The overall goal of the project was to better understand the hierarchy of factors that influence occupancy and density of kori bustard and helmeted guineafowl populations within the Northern Tuli Game Reserve and how landscape conservation and usage affect these factors. Kori bustard densities were highest in areas of sparse vegetation with 5.02 birds per square kilometer in field season one and 2.20 birds per square kilometer in field season two. We found that kori bustards more often occupied areas of sparse vegetation (field season one ψ=0.35, field season two ψ=0.35) with open canopies (field season one ψ=0.37, field season two ψ=0.39) and lower elevation (field season one ψ=0.39, field season two ψ=0.46). Helmeted guineafowl were found at a higher density in areas of dense vegetation at higher elevations with 950 individuals per square kilometer in field season one and 2,368 individuals per square kilometer in field season two. We also found that helmeted guineafowl occupancy was most influenced by dense vegetation (field season one ψ=0.80, field season two ψ=0.75) and closed canopy (field season one ψ=0.85, field season two ψ=0.75. We then use the gathered information about both species density and occupancy on a broader scale to show how landscape conservation planning could have a positive impact on the study site and surrounding area. By determining which habitat and landscape factors influence kori bustard and helmeted guineafowl density and occupancy we are able to better conserve both species and species that utilize the same types of habitats and resources.

Effects of wind turbine noise on male Greater Prairie-Chicken vacalization and chorus - Cara Whalen

  • Thesis Defense
  • 11/30/2015

Wind energy facilities are being constructed without full knowledge of their effects on birds, and the noise generated by wind turbines is a particular concern. I investigated the effects of wind turbine noise on male Greater Prairie-Chicken (Tympanuchus cupido pinnatus) vocalizations and chorus near Ainsworth, NE, USA in 2013 and 2014. I studied 14 leks located in the area surrounding a 36-turbine wind energy facility. I used two main approaches in this study. First, I recorded the sound of Greater Prairie-Chicken boom, cackle, whine, and whoop vocalizations at each of the study leks and measured the duration, sound pressure level, peak frequency, dominant frequency, fundamental frequency, bandwidth and nonlinearities of each vocalization. I used linear models to determine if the vocalizations at leks near the wind energy facility differed from vocalizations at leks farther away. I found that within 1000 meters of the wind energy facility, boom and whoop sound pressure levels were higher, boom duration was shorter, whine fundamental frequency was higher, and cackle biphonations occurred less often. These differences suggest that male Greater Prairie-Chickens are adjusting aspects of their vocalizations in response to wind turbine noise. In the second approach, I placed audio recorders along transects extending from leks to record the sound the Greater Prairie-Chicken chorus. I also placed audio recorders at locations in a grid formation overlaid on the wind energy facility. I created models to describe the how the chorus and wind turbine noise were affected by covariates. I used the models to predict levels of the chorus and wind turbine noise and assess the potential for wind turbine noise to mask the chorus under specific scenarios. The results suggested that wind turbine noise may have the potential to mask the Greater Prairie-Chicken chorus, but the extent and degree of masking is uncertain.

Population Dynamics and Movement of Channel Catfish in the Red River of the North - Steve Siddons

  • Thesis Defense
  • 11/25/2015

Channel Catfish are widely distributed across North America and highly valued as a sport fish and for food. While most Channel Catfish fisheries are managed under liberal harvest regulations, the Red River of the North (Red River) in Manitoba, Canada is managed with restrictive harvest regulations to promote a trophy fishery for Channel Catfish. Our objectives were to: 1) analyze population dynamics of the trophy population of Channel Catfish on the lower Red River, 2) compare population characteristics of Channel Catfish at selected reaches throughout the Red River in Manitoba, and 3) determine movement characteristics of Channel Catfish and the permeability of the St. Andrews Dam on the lower Red River. We found lower Red River Channel Catfish were commonly reaching ages greater than 20, growing slowly, and had a low mortality rate. Trophy Channel Catfish were most common below the dam on the lower river, and small and intermediate sized Channel Catfish were most common on the upper-most sites we studied. Long distance, upstream movements (> 500 kilometers) were common for large (>600 mm) Channel Catfish. This research provides insight into the age, growth, and mortality of a trophy fishery for Channel Catfish. We believe restrictive harvest regulations have preserved the integrity of this fishery and are adequately maintaining the age and size structure of lower Red River Channel Catfish.

Phosphorus loading potential of agricultural soils in the United States - Becky Young

  • Dissertation Defense
  • 11/20/2015

Phosphorus (P) is one of the leading causes of surface water quality decline in the United States, leading to algal blooms and hypoxia in lakes and streams. Decreasing conservation funds dictate that agencies such as the Natural Resources Conservation Service, maximizes its effectiveness and efficiency in implementing practices to address P management and runoff on agricultural lands. Additional information on P behavior in soil is needed to improve P management plans to reduce pollution risk at the watershed, farm, and field scales. This research focuses on the development of total soil P release models, to be included into assessment and management tools to better identify agricultural soils that pose the greatest threat to surface water if eroded, and to improve existing nutrient loss models.

Soil P sorption behaviors and relationships with other soil properties were investigated on 313 agricultural surface soils from across the U.S. Different soil grouping schemes were investigated when analyzing and modeling soil P sorption behaviors at the national-level. Three large watershed areas with known P issues were also investigated to compare watershed-specific models to overall national-level models.

Overall results showed that, (a) oxalate extractable and Mehlich-3 extractable P tests are the most appropriate soil P tests for estimating total P release and P adsorption in most soils, (b) total P release prediction models improve when soils are grouped based on their calcium carbonate content and degree of weathering or modeled at a large watershed level, than at a general national-scale, (c) the majority of statistically significant and reliable total P release prediction models include clay and either oxalate or Mehlich-3 extractable Al, (d) potential risk models can differ greatly within a given area or watershed, depending on the employed modeling scheme (i.e. area-specific vs. national-level), and that (d) with further research and refinement, the relationships and models developed in these studies have the potential of improving current P Indices and assessment tools, and subsequent management recommendations and practices.

Three dimensional wind speed and flux measurement over a rain-fed soybean field using orthogonal and non-orthogonal sonic anemometer designs - Taylor Thomas

  • Thesis Defense
  • 11/16/2015

The eddy covariance method for estimating fluxes of trace gases, energy and momentum in the constant flux layer above a plant canopy fundamentally relies on accurate measurements of the vertical wind speed. This wind speed is typically measured using a three-dimensional ultrasonic anemometer. Previous studies comparing designs with orthogonal transducer sets to designs with non-orthogonal transducer sets suggest differences in measured 3D wind speed components, in particular vertical wind speed, from the non-orthogonal design relative to the orthogonal design. These differences, attributed to additional flow distortion caused by the non-orthogonal transducer arrangement and support structure, directly affect fluxes of trace gases, energy and momentum. A field experiment was conducted over a rain-fed soybean field at the AmeriFlux site (US-Ne3) near Mead, Nebraska to quantify these differences. Ultrasonic anemometers featuring orthogonal transducer sets (ATI Vx Probe) and non-orthogonal transducer sets (Gill R3) collected high frequency wind vector and sonic temperature data. The vertical component of wind speed was underestimated in the non-orthogonal design relative to the orthogonal design. Consequently, the non-orthogonal Gill R3 models underestimated sensible heat flux by 11% and friction velocity by 5% relative to the ATI Vx orthogonal design under the same atmospheric conditions.

A Desert in Disguise: The Resilience of the Nebraska Sandhills - Jeff Hartman

  • Dissertation Defense
  • 11/2/2015

The Nebraska Sandhills are the largest sand dune system in the Western Hemisphere, and are unique in that it they remain relatively undisturbed from row crop agriculture. Research in the past two decades demonstrated that the Sandhills are dynamic on millennial timescales, switching between stabilized, vegetated states to non-vegetated, mobilized states. Currently, mixed-grass vegetation stabilizes the Sandhills, but understanding how ecological processes are altered as sand dunes transition from stabilized to mobilized states provides insight into the thresholds, stability, and resilience of this grassland sand dune ecosystem. My research investigated the impacts of experimental vegetation disturbances on ecological processes and the sand dune surface stability. For ten years (2005-2014), Press, Pulse, Grazed, and Control treatments were applied to stabilized sand dunes. Press treatments killed vegetation and prevented re-growth, while Pulse treatment killed vegetation in one year and then allowed two years of recovery. I measured changes in key ecosystem processes (aboveground biomass, nitrogen cycling, soil respiration, and soil C and N pools) as sand dunes transitioned from stable to mobile states. I found that Press vegetation disturbance led to mobile sand dunes after 4-5 years. However, there was a time lag between complete loss of aboveground vegetation and increased erosion, which indicates that belowground ecological functioning buffers disturbances and is important in controlling sand dune surface stability. The Pulse treatment reduced aboveground biomass and shifted the system to an annual and C3 grass dominated plant community, but belowground functioning continued at reduced rates and erosion was minimal. However, in the 11th year of the study, the variance in the erosion activity increased, potentially foreshadowing a state shift in the Pulse treatment. A severe drought in 2012 produced similar impacts on ecosystem processes as the Pulse treatment, reducing aboveground biomass and increasing the contribution of forbs. The 2012 drought also increased available soil nitrate and ammonium while reducing net N mineralization and soil CO2 flux, but did not cause measurable erosion. My results indicate that the Nebraska Sandhills are resilient to climate and vegetation disturbances on decadal timescales, and that continued belowground functioning is critical to the stability of this ecosystem.

Assessment of disturbance effects of an existing wind energy facility on greater prairie-chicken (Tympanuchus cupido pinnatus) breeding season ecology in the Sandhills of Nebraska - Jocelyn Harrison (Olney)

  • Thesis Defense
  • 7/24/2015

Recent wind energy development in the Great Plains of North America has given rise to concerns of potential impacts on the greater prairie-chicken (Tympanuchus cupido pinnatus). Recent studies in fragmented landscapes have suggested greater prairie-chickens may avoid wind facilities, which may restrict them to less suitable habitat and lower their chances of reproduction and survival. But, it is unknown if there is a similar effect in contiguous grass landscapes. Thus, we investigated the effect of a pre-existing, 36-turbine wind energy facility on greater prairie-chicken nesting, brood-rearing, and spatial ecology in the Nebraska Sandhills. We captured and marked 78 female greater prairie-chickens along a 24-km disturbance gradient leading away from the wind facility in 2013 and 2014, and used radio and satellite telemetry to monitor females throughout the breeding seasons. We located and monitored 91 nests and 31 broods, and recorded habitat, temporal, and weather covariates for nest and brood locations throughout the study period. Proximity to the wind energy facility did not affect greater prairie-chicken nest site preference or nest survival. We also found no effect of the wind energy facility on greater prairie-chicken brood site preference or survival. With regard to greater prairie-chicken spatial ecology, we found no significant difference between home range area for females that were near or far from the wind energy facility, and no association of space use with distance to the nearest wind turbine for females in close proximity to the wind energy facility. Our results suggest that greater prairie-chicken nesting, brood-rearing, and spatial ecology is not influenced by the presence of the wind energy facility in an unfragmented grassland landscape. This information will be useful as regulatory agencies develop siting and operational policies for wind energy facilities and will contribute to range-wide greater prairie-chicken management strategies.

HOUSE SPARROW DECLINES AND DISTRIBUTION: A BYPRODUCT OF URBAN GREENING? - Jessica Burnett

  • Thesis Defense
  • 7/11/2015

Chair: Michael P. Moulton Co-chair: Kathryn E. Sieving Major: Wildlife Ecology and Conservation The decline of House Sparrows (Passer domesticus) in its native range over the last few decades has prompted an increase in population monitoring and assessment in the UK and mainland Europe, where this species is native and widespread. Across its native range, the House Sparrow was historically ubiquitous across the urban-rural gradient, however, has declined across this gradient over the last three decades. House Sparrows were once ubiquitous in the backyards of North America but may no longer be a common sight in residential areas in some parts of North America, such as Florida. The literature documenting the backyard and urban decline of House Sparrows in North America is scant. A minimal understanding exists regarding North American urban House Sparrow distributions and population trends, relative to that of European research. Both the severity of declines and the resulting distribution of House Sparrows in North American urban areas are not clearly understood. Understanding the current distribution of urban House Sparrows may aid our understanding of where and why this species, is declining in human-dominated areas. With this in mind, I approached the problem from two angles. First, I analyzed population trends of House Sparrows using Florida Christmas Bird Count (CBC) data. I ran linear regressions on select Florida CBC circles at two time scales: CBC years 51 to 112 and years 98 to 112. Of the circles with significant slope parameter estimates, I conducted a multivariate analysis of variance (MANOVA) on the first two principal components of the habitat variables within each CBC circle, and the latitude of the circle center. Second, I conducted point counts in urban and residential areas of Gainesville, Florida to understand the relationship between urbanization and House Sparrow distributions and declines. I conducted 119 repeated-point counts (total surveys = 238) from May to September 2014 in two habitat types across Gainesville, FL, commercial and residential, using a stratified random sampling technique. I conducted single-season occupancy models to determine whether covariates of land use and the distance to the nearest occupied site affected the probability of site occupancy (ψ) by House Sparrows urban areas. Of the 44 circles I analyzed, 20 had declining trends on the long-term scale, but only 4 showed significant declines on the short-term scale. Linear regressions on the raw data were not qualitatively different than linear regressions on the effort-scaled data (i.e. birds per party-hour). Despite repeated efforts I detected no House Sparrows in residential sampling areas. Moreover I detected House Sparrows at only 14 of 119 (18 %) of the point count sampling sites. Amount of land devoted to commercial uses, and the distance to the nearest occupied sampling site best-predicted House Sparrow occupancy. I used model averaging to estimate effects of land use and distance on ψ. Model-averaged estimates of ψ was 1.24% (±2.3% unconditional SE), and the probability of detection (p) was 65% (±1.5% unconditional SE), respectively. House Sparrow occupancy was not significantly associated with any other species. I thus confirmed the rarity or, more likely, the absence of House Sparrows in residential areas of Gainesville, Florida. Although House Sparrow presence can be best predicted by the amount commercial habitat (e.g., particularly near grocery stores), their occupancy of these sites was much lower than one might expect of a once-ubiquitous and successful invader. The importance of the decline of this highly successful invader is underrepresented in North American ornithological literature. This study documents the phenomena of the possible disappearance of House Sparrows from residential habitat and the condensed occupancy or low densities in commercialized areas (in seemingly ideal House Sparrow habitat).

Carbon Storage and Potential of Windbreaks on Agricultural Lands of the Continental United States - William Ballesteros

  • Dissertation Defense
  • 6/26/2015

Agricultural production systems face major challenges under climate change scenarios, in terms of expected negative impacts on productivity and persistence of the crops. Greenhouse gases (GHG) from agriculture continue to rise although not as fast as from other fossil fuel-based human activities. Windbreaks perform several ecosystems functions that improve the local and regional capacity of crop systems to increase yields and offer environmental services by minimizing the negative effects of extreme weather events. Field windbreaks also represent an important means of mitigating greenhouse gas emissions. This is predominantly accomplished by the windbreak trees storing carbon (C) in their above and belowground woody tissue while reducing carbon dioxide (CO2) emissions either through avoidance of emissions or through energy savings. However, available and reliable data for estimating crop windbreak contributions to whole-farm and regional C assessments are scarce and in most regions do not exist.

We investigated the C storage potential of windbreaks and the extent of potential reduction in emissions due to the presence of windbreaks in different farming scenarios in the Continental U.S. We compared the performance of many allometric equations to determine the C storage potential of some windbreak tree species in different regions of the continental U.S., 2) analyzed the reduction of carbon equivalent (CE) emissions for different crops by planting windbreaks, and 3) evaluated hypothetical farms synthesized with different windbreak designs together with cropping systems and farmstead. These scenarios were evaluated in the way they best can offset their C emissions.

Jenkin's model was the best tool for estimating biomass/C storage potential for windbreaks. Different windbreak designs can offset C emissions from cropping systems in small and large-scale farms. Windbreaks have an important impact in C emissions reduction when planted in agricultural lands. Two- or three row field windbreaks can offset most C crop emissions. Key aspects of the windbreak potential for offsetting C emissions in farming operations included: site conditions, tree species, house size, windbreak designs, and farmers willingness to adopt these changes. The findings from this project provide further evidence of the role crop windbreaks can play in GHG mitigation in agriculture and describe a reasonable, science-based approach for estimating the level of these contributions.

Green Manures in an Organic Soybean - Winter Wheat - Corn Rotation: Effects on Crop Yields, Soil Nitrate, and Weeds - Katja Koehler-Cole

  • Dissertation Defense
  • 6/16/2015

In organic soybean - winter wheat - corn rotations, animal manure is a common choice to maintain high yields, but leguminous crops grown as green manures (GM) after wheat harvest and incorporated into the soil before corn planting, can be an alternative when manure is not accessible. Forage legumes with high dry matter (DM) production and high biological N fixation have been shown to meet corn N demand. However, in Eastern Nebraska, lack of precipitation can reduce GM growth and N fixation, leading to an insufficient N supply for corn, but corn growth can also be impacted by soil moisture deficits left by GM. Our objectives were 1) to determine the GM potential of four types of forage legumes, and 2) to evaluate management methods that optimize GM benefits.

We conducted an experiment at the ARDC near Mead, NE, from 2011 - 2014. Red clover, white clover, alfalfa, and sweet clover were undersown into winter wheat in early spring. After wheat harvest, they were either mowed or not mowed, and terminated in the fall or the next spring. We measured green manure DM, weed DM, soil nitrate concentrations, and crop yields throughout the rotation. We compared GM effects to effects of cattle manure, post-wheat soybean cover crops, and a control (no fertilizer).

Red clover produced the most DM, up to 5.5 Mg ha-1 and showed excellent weed control, especially when mowed. However, GM did not increase soil N compared to the control. Subsequent corn yields were always significantly higher for manure (7.6 to 8.1 Mg ha-1) than for undersown GM, and were lowest after RC in 2012 (2.8 Mg ha-1) and after WC in 2013 (4.6 Mg ha-1), due to the lack of soil moisture after GM or insufficient N production of GM.

In our study, GM established well, but increased corn yields compared to a control in only one of three years. Manure is the most reliable method to maintain high crop yields, but combinations of GM and animal manure could be a tool to increase N availability to corn and decrease N leaching losses after corn harvest.

Resilience Thinking, Adaptive Management, and Optimization for Structured Decision Making in Social-Ecological Systems - Noelle Hart (Chaine)

  • Dissertation Defense
  • 6/15/2015

Natural resource management may be improved by synthesizing approaches for framing and addressing complex social-ecological issues. This dissertation explores how structured decision making processes can be informed by resilience thinking, adaptive management, and optimization. Resilience thinking draws attention to the risks of managing for narrowly-focused objectives, which can reduce natural variability, ignore interactions across scales, and ultimately lead to a sudden transition into an alternative state. Adaptive management highlights the prevalence of uncertainties in complex systems and enables learning through management. Optimization offers ways of conceptually simplifying systems, maximizing multiple objectives, and exploring tradeoffs.

Building from literature review and a mix of actual and hypothetical management scenarios, I describe: (a) how resilience thinking can be linked to the steps of structured decision making, (b) how resilience thinking can contribute to the framing of an optimization problem, and (c) how potential adaptive management projects can be identified and developed as part of a broader structured decision making process. In the conclusion, I combine ideas from the prior chapters, using an oak forest conservation example, to demonstrate how resilience thinking, adaptive management, and optimization can jointly contribute to a structured decision making process. In addition to providing practical advice to managers, the dissertation can facilitate discussion between scholars, technical experts, policy makers, and stakeholders about how decision making approaches can be combined to better balance values (within and across scales), learn, and prepare for surprises in complex social-ecological systems.

Analyzing the Relationship of Soil Moisture and Biophysical Variables in Wet and Dry Seasons at a Rainfed and Irrigated Fields in Eastern Nebraska - Eric Hunt

  • Dissertation Defense
  • 5/19/2015

Agriculture production, particularly of maize and soybeans, is a major component of Nebraska's economy and identity. However, agricultural production in Nebraska faces increasing challenges, particularly in areas dependent on irrigation. One of the larger concerns is the potential for excessive groundwater depletion due to increased demand for food and fuel from Nebraska crops and increasing risks of water stress in growing seasons due to climate change. Given the importance of agricultural production to the state and the increasing environmental risks, it has become essential for a deeper understanding of the soil-plant-atmosphere continuum to help producers make more informed management decisions. One of the variables that producers are starting to use for decision-making is soil moisture. Soil moisture is an integral part of the hydrologic cycle and an essential component in our understanding of land-atmosphere interactions. Improved understanding of soil moisture response under major cash crops, such as maize and soybeans, and insights into the dynamics of the soil moisture-crop-atmosphere continuum are needed to help producers in irrigated regions make more informed decisions.

This presentation will summarize a body of research that analyzed eight years of soil moisture and biophysical measurements from an irrigated and rainfed maize-soybean rotated fields at the UNL ARD over a range of growing season conditions that ranged from abnormally dry and warm to unusually moist and cool. The primary objective is to demonstrate the link between soil moisture and its relationship to crop biophysical variables under varying climate conditions to improve our understanding interactions and crop response. This work showed that soil moisture is a very suitable measure of the effectiveness of precipitation for soil recharge and that timing of precipitation can be almost be as important as quantity. Dry spells occurred in most years of the study period, but the timing and duration of these dry spells were important for determining how detrimental it was to the rainfed crop. In years where adequate precipitation was received, the measured evapotranspiration and gross primary productivity at the rainfed field increased to a level comparable to the irrigated field. However, during a classic flash drought, prolonged soil moisture stress led to declining stomatal conductance and a significantly reduced maize yield compared to the irrigated field. The flash drought case study not only showed the importance of irrigation during a prolonged dry spell, it also showed the utility of using short-term drought indices, such as the Standardized Precipitation Evapotranspiration Index (SPEI), for identifying water stress of a rainfed field. Thus, short-term indices can be used with more confidence when trying to determine locations where crop yields could be significantly reduced because of water stress.

Pattern of Distribution, Morphological Variation, and Genetic Divergence among Ecuadorian Astroblepid Catfishes - Katherine Lawry

  • Thesis Defense
  • 4/29/2015

The Andean ichthyofauna remains a poorly understood component of Neotropical biodiversity, and stands in stark contrast to the lowland ichthyofauna in terms of number of species and range of distribution. The Climate Variability Hypothesis (CVH) predicts rapid turnover of species along elevational gradients in tropical climates, but it remains unclear whether stream fishes follow this pattern. Astroblepid catfishes represent a distinctive assemblage of species that inhabit high elevation streams throughout the Andes from Panama to Bolivia, and constitute the only native fish family present in the Ecuadorian highland region. In this research, population samples of Astroblepids collected throughout Ecuador's Napo Province over a 1000m elevational gradient were designated a priori into groupings based on external morphological features. Groupings based on morphological features were tested using DNA barcode sequences of the mitochondrial gene cytochrome c oxidase subunit I (COI). Sequences were analyzed in a phylogenetic context using Neighbor Joining and Bayesian Inference of Phylogeny. Results of molecular analyses indicated COI barcode sequence divergence that confirmed morphological designations in 2 of 14 cases, suggested the presence of cryptic diversity in 6 of 14 cases, and failed to explain morphological variation in the remaining 6 of 14 cases. Morphological and molecular categorizations showed no trend with elevation or temperature. Further molecular investigation using nuclear genes may help to resolve discrepancies between analyses and failure to match with morphological designations, and broader geographic sampling may yield more consistent patterns of distribution.

Green Roof Energy Balances for Native Grasses and Sedum - Christopher Schwarz

  • Thesis Defense
  • 4/20/2015

Green roofs offer a possible solution to reduce urban heat island effects caused by urbanization. Conventional green roofs use sedum for plant cover; however, native species are being considered as an alternative cover. More information is needed to understand the potential of native species for green roof use. This study was conducted from July 2013 through October 2013 to quantify the energy balance components and the microclimate for native grasses and sedum on a Midwestern green roof. The results provide evidence that native species are an appropriate choice for Midwest green roof use.

Water quality in agricultural watersheds: Exploring patterns, fluxes and uncertainties using high-frequency data - Kaycee Reynolds

  • Thesis Defense
  • 4/17/2015

The inherently dynamic nature of climate-landscape interactions in agricultural watersheds makes evaluation of nitrate (NO3-) fluxes from these ecosystems complex. Understanding NO3- loading to agricultural streams requires optimization of monitoring strategies. A spatially distributed, high-frequency water quality monitoring network has expanded to cover ~40% of Iowa, providing direct observations of in situ NO3- concentrations at a 15-minute resolution. In this study, NO3- records were systematically subsampled allowing quantification of uncertainty in annual mean NO3- concentration and total flux estimates for conventional sampling strategies. In addition, seasonal trends in nitrate concentration response for more than 400 storms were explored using high-resolution data. As climate becomes more erratic, high-resolution NO3- monitoring will conceivably offer an improvement in our understanding of coupled hydrological and biogeochemical system interactions.

Plant Diversity Affects Success of Invasive Thistles in Restored Nebraska Grasslands - Katilyn Price

  • Thesis Defense
  • 4/17/2015

Invasive plant species threaten native grasslands, affecting nutrient cycling, biodiversity, wildlife habitat, and usable land for production. Consequently, preventing establishment of invasive species is critical before removal becomes difficult and expensive. The purpose of this study was to examine the effects of grassland plant diversity on musk thistle (Carduus nutans) and Canada thistle (Cirsium arvense) establishment and determine which environmental factors (light penetration, soil moisture, plant diversity, and soil nitrogen) account for resistance to invasions. In a field experiment at The Nature Conservancy's Wood River site (Nebraska), the two invasive thistle species were planted into replicated grassland diversity plots. The ¾ acre grassland plots were seeded as monoculture (Andropogon gerardi), low diversity, and high diversity treatments in 2010. The experiment also included plots maintained as bare soil. Actual plant diversity was measured in 2013. Environmental factors were measured during the growing seasons (April-October) of 2013 and 2014. After two years, both thistle species flourished in bare soil plots, maintained populations in monoculture and low diversity plots, while thistles in the high diversity grassland plots emerged but died prior to bolting and flowering. Analyses of the environmental factors show strong declines in resource availability (light, water, nitrogen) associated with both plant biomass and diversity across the experimental diversity gradient.

Ecology and Management of Superabundant Fish Populations - Nathaniel Stewart

  • Thesis Defense
  • 4/13/2015

In some cases, as a result of growth plasticity, fish population biomasses can reach extreme levels; we term these populations superabundant fish populations. Superabundant fish populations negatively affect aquatic communities and the anglers who utilize those communities, necessitating their effective management. However, there are limitations in our understanding of superabundant fish populations. The limitations in our understanding hamper our ability to predict effects on valuable sportfisheries and our ability to effectively manage superabundant fish populations. We need to better understand superabundant fish populations: what are they, how do they interact with other populations in aquatic systems, and how can we effectively monitor and manage them? The overall goal of my thesis research is to provide further insight into the ecology of superabundant fish populations and to provide information that will aid in their effective management. I describe a method for estimating population sizes and spatial distributions of superabundant fish and evaluate a management action to control superabundant fish populations using white perch (Morone americana) and gizzard shad (Dorosoma cepedianum) populations in southeastern Nebraska reservoirs as models.

The Occurrence and Ecological Effects of Amphetamine Type Stimulants on Aquatic Organisms - Alexis Paspalof

  • Thesis Defense
  • 4/13/2015

The occurrence of pharmaceuticals, illicit drugs and their bioactive metabolites in aquatic environments has become an increasingly important topic worldwide. While it is increasingly evident that these compounds occur in surface and ground water impacted by wastewater, the potential ecological effects from their exposure to aquatic organisms are virtually unknown. The focus of this study is to better understand both the occurrence and potential effects of amphetamine type stimulants (ATSs) in wastewater-impacted environments. First, samples were collected and analyzed for pharmaceuticals, including ATSs, in two different watersheds downstream from the highly populated Hudson River, in New York and Gwynn Falls in Baltimore, Maryland. These two watersheds were chosen because each had stations that were part of existing long-term ecological studies. Although much was known about the ecology of these highly urbanized watersheds, little data is available indicating contamination from pharmaceuticals and ATSs. While not highly prevalent, amphetamine (AMPH) was detected at one site in the Hudson River and consistently detected at low concentrations in all Gwynn Fall sites. The occurrence of all pharmaceuticals was related to other indicators showing the presence of wastewater effluent.

In addition to the field sampling, the potential effect of ATS exposure to aquatic ecosystem function was measured using exposed microbial biofilms to environmentally relevant concentrations of amphetamine. After 3 weeks, dissolved amphetamine exposure in stream mesocosms suppressed gross primary production and community respiration, despite a significant decrease in the parent compound concentration. Based on field and laboratory work, chronic exposure to environmentally relevant concentrations of ATSs and other pharmaceuticals may affect ecosystem functions and the organisms that depend on these functions. Finally, because catecholamine production is known to be affected by stimulant exposure in higher organisms, an experiment was conducted to evaluate aquatic organism exposure to dopamine (DA). Current literature indicates the presence of DA in marine algae, and its production is thought to help control predation. This study reports the biological effects DA has on freshwater algae at concentrations similar to environmental concentrations in marine environments.

Civic Capacity and Integrative Public Leadership: A Case Study of the Nebraska Water Leaders Academy - JoLeisa Cramer

  • Thesis Defense
  • 4/10/2015

This study explored the impact of the Nebraska Water Leaders Academy (NWLA) on natural resource management by investigating a link between civic capacity and integrative public leadership in the context of adaptive governance. This mixed mode case study utilized a comprehensive, quantitative on-line questionnaire on civic capacity and integrative public leadership as well as qualitative interviews completed by NWLA alumni. The study included 31 questionnaire responses from NWLA alumni, 53 alumni-chosen rater responses, and 21 interviews.

NWLA alumni were found to frequently employ their civic capacity and integrative public leadership skills to promote and improve collaborative natural resource management. There was a statistically significant relationship between civic capacity and two elements of integrative public leadership resources - integrative leadership resources and integrative structures and processes from both the alumni and raters' perspectives. Thirteen individual themes emerged from the case study of the NWLA that provide insight into how alumni are conducting integrative public leadership. This study establishes a baseline for the link between leadership and natural resources management.

Coupling soil O2 and greenhouse gas dynamics - Karla Jarecke

  • Thesis Defense
  • 4/3/2015

Dynamic soil hydrology triggers important shifts in soil biogeochemical and physical processes that control greenhouse gas (GHG) emissions. Soil oxygen (O2), a direct control on biogenic GHG production (e.g. nitrous oxide-N2O, carbon dioxide-CO2 and methane-CH4), may serve as both an important proxy for determining sudden shifts in biogenic GHG production as well as the physical transport of soil GHG to the atmosphere. Recent technological advancements offer opportunities to link in-situ, near-continuous measurements of soil O2 concentration to soil biogeochemical processes and soil gas transport. Using high frequency data, this study asked: Do soil O2 dynamics correspond to soil GHG concentration and GHG surface flux? Daily change in subsurface CO2 and N2O concentrations were inversely related to daily change in soil O2 dynamics at 10 and 20 cm whereas CH4 concentrations did not change in response to soil O2 concentration dynamics. Meanwhile, daily change in surface CO2, N2O, and CH4 fluxes were not significantly related to change in daily soil O2 concentration. Our study suggests that coupling near-continuous soil O2 concentration and soil gas flux under dynamic soil hydrology may lead to greater understanding of climate change feedbacks and serve as a relevant predictive tool for future climate change mitigation.

Soil preferences of Nicrophorus beetles and the effects of compaction on burying behavior - Kelly Willemssens

  • Thesis Defense
  • 3/19/2015

The American burying beetle, Nicrophorus americanus Olivier, is the largest North American member of the Silphidae. It was declared federally endangered in 1989 and many efforts to prevent this species from going extinct are ongoing. The Nicrophorus beetles bury small carcasses for reproductive purposes. They also reside in the soil during times of daily and seasonal inactivity. To better understand why the American burying beetle is in decline, the importance of texture, moisture, vegetation, and gravel, the burial depth, and the effect of compaction on their burying behavior were examined.

Acute Toxicity of β-N-methylamino-L-alanine (BMAA) to Fathead Minnow (Pimephales promelas) and Zebrafish (Danio rerio) - Jiayi Wang

  • Thesis Defense
  • 1/13/2015

β-N-methylamino-L-alanine (BMAA) is a neurotoxic amino acid produced by most species of cyanobacteria. BMAA has been hypothesized as the cause of ALS and possibly Parkinson's and Alzheimer's diseases for several decades. Both in vitro and in vivo experiments revealed that BMAA can damage motor neurons and cause motor dysfunctions. However, the exact mechanism of BMAA-induced neurotoxicity has not been well understood.

In spite of its water-soluble and non-protein nature, BMAA is able to bioaccumulate in organisms. The ubiquity of cyanobacteria and the bioaccumulation of BMAA, arouse wide human health concern. Previous investigations into toxicity of BMAA mainly focused on various mammalian test models, including rats, mice and primates. However, the toxic effect of BMAA on aquatic organisms has attracted limited attention. Due to the potential for widespread BMAA production in aquatic ecosystems, it is important to understand the toxicity of BMAA in aquatic organisms, such as fish, from an ecotoxicological perspective.

Because limited information exists about how BMAA influences fish, we investigated the acute toxic effect of β-N-methylamino-L-alanine (BMAA) on two widely adopted model fish: fathead minnow (Pimephales promelas) and zebrafish (Danio rerio). The 96 h toxicity tests revealed that BMAA is not acutely lethal to fathead minnow (juveniles: 96 h LC50 > 10 mg/L; larvae: 96 h LC50 > 10 mg/L) or zebrafish (larvae: 96 h LC50 > 10 mg/L; embryos: 10-day LC50 > 100 mg/L). However, BMAA significantly affected the heart rate of zebrafish embryos. Additionally, in the zebrafish embryo-larvae behavioral assay, a range of locomotor function anomalies in zebrafish embryo-larvae exposed to BMAA were observed. On one hand, BMAA was found to accelerate the onset of spontaneous contractions and enhanced touch-evoked contractions. On the other hand, BMAA reduced performance in touch-evoked escape, free swimming and startle response.

To our knowledge, we are the first to investigate the acute toxicity of BMAA in fathead minnow and its behavioral effects on fish. The finding that BMAA influenced locomotor behaviors of fish is of both neurotoxicological and ecological importance.

Habitat and Site Selection of Pheasants and their Hunters During the Hunting Season - Lindsey Messinger

  • Thesis Defense
  • 12/19/2014

While predation has obvious mortality costs for prey, equally as strong non-consumptive impacts of predation have been the focus of recent studies. Not only are prey impacted by their predators through both consumption and fear of predation, but predators are driven by selection to respond to prey behavior and their role should not be discounted. We show how habitat decisions made by highly mobile predators and their prey are dynamically linked, Recreational hunters (predators) make decisions about where to hunt based on a variety of resources (potential prey abundance, proximity to home) and we show that hunters preferentially select hunting locations where the density of primary habitat for their prey, Ring-necked Pheasant, is greatest despite other resources (roads, towns). Targeted habitat selection by hunters as well as distinct periods of prey availability due to regulated hunting seasons create a spatially and temporally variable environment of predation risk which prey are capable of responding. We found that female pheasants increased their home range size and shifted the center of their core home range in response to high levels of hunting pressure at the onset of hunting season. However, these responses diminished over time. Male survival during the first few weeks of the hunting season further confirmed the sort-term impacts of high hunting pressure early in the season. Our data demonstrate factors influencing both predator and prey habitat decisions and give a more holistic view of a predator-prey interaction with implications for wildlife managers concerned with maintaining healthy populations of both predator and prey.

Migratory stopover responses to local and regional change: habitat decisions in a vanishing landscape - Caitlyn Gillespie

  • Thesis Defense
  • 12/17/2014

Understanding the consequences of anthropogenic change for migratory species is challenging because although they have evolved to cope with environmental uncertainty, migrants still rely on predictable relationships within and among habitats to make informed decisions. Calidris shorebirds rely on ephemeral wetlands during northward migration through mid-continental North America, where favorable habitat conditions are annually and regionally unpredictable and increasingly altered by land-use change. We assessed shorebird habitat use in a highly-altered landscape, the Rainwater Basin (RWB), and examined seasonal patterns in food abundance, water availability, and vegetation within and among wetlands. To understand how the landscape mediates stopover decisions, we also monitored Calidris stopover in the Prairie Pothole Region (PPR), where anthropogenic change is less pronounced and wetlands occur in higher densities. Our results indicate that invertebrate and migration phenology are highly correlated, but invertebrate abundance did not predict shorebird abundance at wetlands in the RWB. We also find that while habitat structure predicts shorebird occupancy, and is similar in both regions, wetlands in the PPR supported a higher abundance of Calidris shorebirds than wetlands in the RWB. Our results suggest that that value of stopover habitat is ultimately constrained by landscape-scale habitat availability, as migrants appear to exhibit a threshold response to water availability on the landscape.

Bioenergetics and Habitat Suitability Models for the Chinese Mystery Snail - Danielle Haak

  • Dissertation Defense
  • 12/15/2014

n/a

Community Gardens as Urban Social-Ecological Refuges: Case Studies in Vienna, Austria, Lincoln, Nebraska, and New York City - Joana Chan

  • Dissertation Defense
  • 12/3/2014

Urban community gardens have reemerged in popularity over the past decade in response to social, economic, and environmental changes. The purpose of this multi-case study dissertation was to explore community gardening in the Global North and its contributions to social-ecological resilience in a contemporary urban context. From 2011 to 2014, I conducted qualitative case studies on community gardens in Vienna, Austria, Lincoln, Nebraska, and New York City post-Hurricane Sandy. Considered together, these case studies suggest that community gardens can function as "urban social-ecological refuges" to support resilience in cities. As urban social-ecological refuges, community gardens have the potential to not only carry and transmit cognitive and biological means for facilitating resilience and response capacity by protecting biocultural diversity and social-ecological memories, but also serve as restorative physical refuges for communities in disaster contexts, as well as general social and spiritual refuges which can enrich the social-ecological fabric of our increasingly homogenized urban landscapes.

Management of Channel Catfish Ictalurus Punctatus in the Missouri River, Nebraska - Brandon Eder

  • Thesis Defense
  • 11/24/2014

The popularity of catfish Ictaluridae nationally as a sport fish is well documented and angling for catfish on the Missouri River in Nebraska (NMR) is especially popular. A catfish monitoring by the Nebraska Game and Parks Commission (NGPC) began in 1974 and short-term evaluations of Channel Catfish population dynamics have been performed. However, no long term analyses of population characteristics have been conducted since the early 1990s. The focus of this research was to summarize the status of Channel Catfish populations in the NMR and give recommendations for future management. I summarized population characteristics, modeled length limit regulations, and assessed the feasibility of a survey design aimed at gathering effort and catch data from setline anglers. Population characteristics varied among the four reaches studied. Channel Catfish in the upper unchannelized reach had relatively low mortality, moderate population densities and a long life span. The lower unchannelized reach had a population of small, slow growing Channel Catfish with high mortality rates. Population characteristics in the upper channelized reach were similar to those of the LU except relative abundance was greater. The lower channelized reach had the highest mortality and the fastest growing, shortest lived fish in the study. Modeling revealed all reaches except the lower unchannelized reach could benefit from a 380-mm minimum length limit. In all cases, mean total length, mean weight, and yield would increase with a minimum length limit. A maximum length limit would likely not be effective for growing trophy sized fish in the upper unchannelized reach. Setlining is an unknown aspect of the Missouri River catfish fishery. Methods described in this study appear to be a feasible alternative to creel surveys for estimating setline effort and catch.

Combating Eutrophication: An Ecosystem Scale Analysis of Aluminum Sulfate (Alum) and Biomanipulation Restoration Techniques Among 16 Lakes - Christa Webber

  • Thesis Defense
  • 10/3/2014

Eutrophic conditions in lakes and reservoirs in agricultural regions often drive summer blooms of toxic cyanobacteria. Aluminum sulfate (alum) applications are commonly used to control cyanobacteria blooms and restore water quality. However, studies of alum treatments often lack true replication, comparison to reference lakes, or comparison to other restoration techniques, such as an alum and biomanipulation combined or "dual" treatment. Without these comparisons, the variation of treatment response among replicate lakes and restoration techniques remains uncertain. Therefore, I sought to assess how water quality is affected by multiple restoration techniques among geographically proximate (1.4 km2) lakes. I hypothesized that: 1) alum restoration would uniformly improve water quality in replicate lakes via increased nutrient limitation, and 2) dual treatment restoration would out-perform alum treatment alone due to added top-down mechanisms amplifying the alum-only, bottom up mechanisms for water quality improvements. Regardless of lake or restoration technique, the phytoplankton community was dominated by cyanobacteria pre- and post-treatment in each lake. Treatment success was highly variable among replicate lakes. I found trends for overall restoration success were not always representative of average lake condition post-treatment, but were often dominated by extreme responses in a few lakes. Fully understanding how similar ecosystems are affected by alum will help determine if lake alum treatments alone can consistently combat algal toxins and other symptoms of eutrophication. Overall, the alum treatment effectively controlled nutrient levels. However, if restoration goals are more biological, adding biomanipulation as a dual treatment may enhance lake restoration success.

The Hard Winter of 1880-1881: Climatological Context and Communication via a Laura Ingalls Wilder Narrative - Barbara Boustead

  • Dissertation Defense
  • 7/21/2014

The Hard Winter of 1880-1881 was featured in the Laura Ingalls Wilder historical fiction account, The Long Winter, as well as in several town histories across the Plains region. Both meteorological records and historical accounts indicate that the winter was particularly long, snowy, and cold. The question of how "hard" a winter is for a given location depends on the climatological context, which relies on an objective characterization of winter severity. The newly-developed Accumulated Winter Season Severity Index (AWSSI) allows comparison of the winter of 1880-1881 among sites across the region, as well as in the context of the period of record, to quantify its severity. Additionally, investigating the impacts of two large-scale teleconnections, the El Niño/Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO), in the central United States provides context for the influence of both a strongly negative NAO and an El Niño event during the winter of 1880-1881. With an understanding of the climatological factors influencing the Hard Winter, along with the context for its severity, a more thorough analysis then was conducted to quantify and describe its severity. The connection of the winter of 1880-1881 to a popular book written by an author who is a cultural icon provides a natural vehicle with which to communicate weather and climate concepts to multiple non-technical audiences. A narrative constructed around the Little House books, particularly The Long Winter, provides a means of audience engagement and interest in weather- and climate-related topics, which was at least partially quantified by surveying audiences of the narrative. Overall, the scientific background, combined with a familiar narrative voice, provides a means to transmit weather and climate understanding to a wide audience.

A Case Study of Changing Cropping Diversity and Agricultural Risk in the Doulthabad1 Mandal of Telangana State in India - Srikanth Kondabolu

  • Thesis Defense
  • 7/15/2014

The Doulthabad1 Mandal is a hot semi-arid agro ecological sub-region (Rao et al 2006) located in Mahbubnagar District on the North Telangana Plateau in the state of Telangana2. Agriculture is the main occupation in this region, which is populated mostly with small and marginal farmers. This study uses the time period from 1971 to 2004 to study the variation in cropping pattern diversity and distribution of rainfall during the monsoons and understand the implications on production risk in agriculture. Quantitative methods were used in determining the changes in rainfall while qualitative methods were used to study cropping system changes. The analysis of rainfall data indicates a 5% increase in wet spell duration and a 5% decrease in wet spell intensity in the period from 1971-1990 to 1991-2004. The cropping system diversity in the same time period has decreased from 23 to 10 crops in the Kharif (monsoon) season with access to improved agricultural technology. These changes are also associated with a shift from inter cropping to mono crop based systems. The results indicate that these changes in cropping systems have resulted in a decreased management of production risk with increased investments in agriculture and lesser flexibility in the decision making on crops.


1 Doulthabad is a Mandal (a sub divisional administrative unit of Districts in India) in Mahbubnagar District (an administrative unit of a state in India) of Telangana state in India.

2 The new state of Telangana was formed on 2nd June 2014 after it had separated from the earlier state of Andhra Pradesh.

An Evaluation of Climate-Land Surface Model Weather Forecasts for Nebraska; Phenological and Yield Sensitivities of Corn (Zea Mays. -L) to Irrigation. Mead, Nebraska, USA. - Jane Okalebo

  • Dissertation Defense
  • 7/14/2014

Nebraska's climate is highly variable and is expected to change resulting in warmer spring and summer temperatures coupled with more erratic rainfall events. Groundwater records show that the Ogallala Aquifer levels are declining. These factors could result in large negative impacts on corn production in Nebraska where about 70% of corn is under irrigation. Weather forecasts and knowledge of the yield, phenological sensitivity of corn to water, temperature and Growing Degree Days (GDDs) are vital in establishing mitigation strategies given the looming weather changes and water resource scarcity. The research below was undertaken to serve as a basis for quantifying possible future impacts.

The usefulness of climate models and land surface models (LSM) hinges on their accuracy. Two candidate LSMs were evaluated: the Noah and the Community Land Surface Model (Version 3.5). The performance of WRF-Noah and WRF-CLM in predicting temperature and precipitation in Nebraska in a dry (2002), a moderate (2005), and a wet (2008) year were evaluated using observed station data downloaded from the High Plains Regional Climate Centre website and PRISM datasets from Oregon State University. These findings are useful in selecting useful models that can be applied to make weather predictions in the near future for yield predictions and decision making.

In addition, the effects of microclimate on corn phenology and yield respectively were explored. This included the influence of temperature and GDDs on corn phenology for both irrigated and rainfed fields. Results of this study can be used to support the selection of longer maturing hybrids that take advantage of increasing temperatures. The sensitivity of corn to water stress in different growth periods was examined. Since crops are not equally sensitive to growth in all stages of their development, a multiplicative empirical model was developed that utilizes actual and potential evapotranspiration as input in determining crop yields for Mead, Nebraska.. The model was calibrated and validated using multiple year corn yield data from the University of Nebraska's Carbon Sequestration Project (CSP) Agricultural Research Sites located near Mead, NE. The new coefficients were not found to be an improvement over the Meyer coefficients (1993), These results support the fact that the robustness of a model depends on the range of conditions over which it is calculated. The model is a tool that can assess deficit irrigation strategies and the impact on yields offering a means of sustaining high yields in the future.

Informing Flood Plain Wetland Restoration with Amphibian Monitoring - Ashley Vanderham

  • Thesis Defense
  • 7/14/2014

Wetlands are among the most important and complex ecosystems in the world. They contribute to nutrient cycling, the hydrologic cycle, and provide critical habitat for many plants, fish, and wildlife. Channelization of Missouri River resulted in the loss of many floodplain wetlands. Recognition of the importance of wetlands has led to legislation that has increased wetland restoration. Despite ongoing restoration efforts, there are few ecologically-based performance guidelines, and managers need methods to quantify and assess the success of restored riverine wetland systems. In 2008 a multi-institutional project funded by the U.S. Army Corps of Engineers was initiated in four states (Kansas, Missouri, Iowa, and Nebraska). The main goal of the project is to assess the success of previously restored wetlands and to create wetland restoration guidelines for future use. To determine restoration success, herpetofauna monitoring was established on previously restored wetlands. Frog call surveys and tadpole dip net surveys were conducted and analyzed using occupancy techniques to help determine restoration success. Amphibians were chosen for monitoring because they are globally declining, they integrate terrestrial and aquatic environments, and because they are good indicators of wetland restoration success. This seminar reports the results of herpetofauna monitoring from three Missouri River bends in Nebraska, a subset of the overall project.

I report on a comparison of frog call surveys and tadpole dip net occupancy results, a novel co-occurrence analysis for frog call surveys, and a functional connectivity analysis based on anuran dispersal distances, and describe how this contributes to the goal of defining successful wetland restorations.

Hydrologic Mediation of the Spatial and Temporal Variability of the Soil CO2 Stable Isotopic Composition of a Subalpine Watershed - Theresa Lorenzo

  • Thesis Defense
  • 6/6/2014

Stable carbon isotope analysis is commonly used to interpret biological and physical processes that affect the exchange of carbon between terrestrial ecosystems and the atmosphere. Estimating the isotopic composition of ecosystem carbon fluxes in relation to variable hydrologic conditions, and in particular variable soil moisture, remains a challenge due to the complexity introduced by landscape morphology and resulting physical gradients that redistribute resources such as water, energy, and substrate. I investigated the effects of variable soil moisture as influenced by landscape morphology on the concentration and isotopic composition (δ13C-CO2) of soil CO2. I measured the δ13C-CO2 and concentrations of soil CO2 at depths of 5, 20, and 50 cm across seven transects in two subalpine watersheds in the Tenderfoot Creek Experimental Forest, Montana. My results show that soil CO2 concentration and soil δ13C-CO2 vary systematically with topography and soil moisture gradients. Riparian areas with high soil moisture had higher concentrations and more negative soil δ13C-CO2, whereas upland areas with low soil moisture had lower soil CO2 concentrations, and more positive soil δ13C-CO2. Additionally, the seasonal soil moisture drydown resulted in decreased soil CO2 concentration and an increase in soil δ13C-CO2. These changes are consistent with those predicted by biological and physical processes that are linked to soil moisture, such as plant carbon isotopic discrimination and physical diffusion. The results of my study suggest that landscape structure is systematically linked to the distribution and spatial organization of ecosystem carbon exchange and can be used to interpret and predict terrestrial carbon processes.

Evaporative drivers and hydrologic influences using energy and water budget techiques at a shallow saline lake in the western Sandhills Nebraska, USA - Colin Peake

  • Thesis Defense
  • 6/5/2014

The western Sandhills of Nebraska contain many shallow lakes and wetlands that interact strongly with groundwater and the overlying atmosphere. The region is semi-arid, and most of the lakes are saline, supporting a wide range of ecosystems. Water levels and salt concentrations are highly sensitive to variations in precipitation, evaporation, and groundwater fluxes, making the Sandhills an excellent laboratory for examining the effects of climate on the water balance of interdunal lakes. In this study, we investigate the atmospheric controls on evaporation rates, as well as the water balance of Alkali Lake, one of the more saline lakes in the western Sandhills. The Bowen ratio energy budget and mass-transfer methods are applied over a three-year period (2007-2009) to quantify summer evaporation rates. Daily evaporation is found to vary widely, but averages around 5-6 mm/day during the summer. Evaporation rates are largely controlled by solar radiation on a seasonal basis and by variations in wind and vapor pressure gradient at shorter timescales. Adjustments for salinity affected the mass transfer method more than energy budget method, with a root mean squared error of 0.49 mm/day, but only 0.09 mm/day for the energy budget method. Evaporation dominated the water balance during the summer months, exceeding precipitation by a factor of 3.2, on average. The lake water balance also indicates that evaporation exceeds the sum of all water inputs during summer months, causing lake levels to decrease in summer and rebound during the winter. Net groundwater is the largest source of water to the lake, and averages 2.5 mm/day into the lake. Occasional negative net groundwater values indicate complex interactions between the coupled lake and groundwater systems. Lake reactions to precipitation inputs suggest short term groundwater flow reversals are possible.

Understanding Recycling Behavior of University Students - Prabhakar Shrestha

  • Dissertation Defense
  • 4/21/2014

Thermodynamic reality points to the need to recycle materials in order to build more sustainable economies and communities. This will require behavioral change. This is the case as many people are unable to exercise better choices because they find themselves locked into unsustainable patterns represented in habits, routines, lack of knowledge, institutional structures, inequalities in access, social expectations, and cultural values (Jackson, 2005; McKenzie-Mohr & Smith, 1999). Sustainability strategies that include more recycling, repair, reuse, home composting, and sustainable consumption, require a change in these patterns (Wilson, 2007). Also, most people are not in positions of power where they can directly influence government or corporate policy, although everyone consumes materials and energy in their daily lives, and as such, each person can choose to adopt behaviors that are comparatively better for the environment (Osbaldiston & Schott, 2012).The focus of this research is on enhancing the scientific understanding of the internal interests and motivations of human beings relative to recycling choices, such that policies could be developed and programs implemented to "nudge" people towards changing their behavior. Results point to a substantial role of empathy in explaining recycling choices, especially for UNL students.

Development modeling of Lucilia sericata and Phormia regina (Diptera: Calliphoridae) - Amanda Roe (Fujikawa)

  • Dissertation Defense
  • 4/17/2014

n/a

Fear and the Phantoms of Predators Past - Jessica Laskowski

  • Thesis Defense
  • 4/9/2014

Predator-prey interactions elicit shifts in prey behavior, physiology and life-history that can impact prey population dynamics and community structure to the same extent as prey consumption. An emerging body of literature addressing the 'landscape of fear' shows substantial immediate impacts of fear on prey hormone concentrations, body condition, behavior and reproductive investment. However, predation risk is temporally variable, and although seasonal increases in prey mortality carry-over to constrain prey abundance after predators have moved on, it remains unknown how long, and to what extent the effects of fear carry-over to impact prey populations. We assessed the temporal carry-over effects of human hunting on reproduction in female ring-necked pheasants (Phasianus colchicus). Because harvest is limited to males, but both sexes experience similar cues indicative of risk, we were able to isolate the effects of fear from the selective effects of predation. We found that although hunting did not have prolonged effects on female survival, body condition or nest site selection, females on heavily hunted sites had elevated baseline corticosterone concentrations that were more sensitive to body condition such that birds in poor condition had disproportionately higher corticosterone concentrations on high risk sites. Furthermore, hunter activity caused females to produce 10% smaller eggs. Our results indicate that fear alone can carry-over to impact prey physiology and reproductive investment after cues indicative of risk are gone, and that fear associated with episodes of heightened predation risk can have prolonged impacts on prey populations even in relatively safe environments.

Improving Drought Management for Transboundary River Basins in the United States through Collaborative Environmental Planning - Crystal Stiles

  • Dissertation Defense
  • 3/31/2014

Increasing demand for water and the uncertainty of climate change have put pressure on the global water supply, presenting one of the greatest challenges of the 21st Century for human development. Drought is a natural hazard that further compromises water supply and increases competition among water use sectors, although it is considered to be a normal part of climate. These challenges confirm the need for comprehensive water supply and drought planning. Planning for water, however, is often conducted within political boundaries that are not consistent with the water resource's natural boundaries, which can result in conflict. Collaborative environmental planning is a relatively new sub discipline of planning that can address the occurrence of drought in a transboundary river basin. While international-level transboundary water resources planning has been well addressed by the literature, little research has been done to explore this type of planning at the U.S. state level. This research answers the following question: How are water planning agencies using collaborative planning to improve the management of drought in transboundary basins in the U.S.?

To address this question, transboundary basins in the U.S. that are planning for drought were identified, and basin-level drought planners were interviewed about drought management strategies, the role of collaboration and coordination in the planning process, and recommendations for drought planning in a transboundary basin based on experiences with successes and barriers. It was found that while the drought planning process is similar for all basins, each basin implements drought management strategies that are unique to their circumstances in the basin. The research also found that collaboration and coordination are necessary components of drought planning for transboundary basins. Recommendations made by interview participants based on their experiences with successes and barriers centered upon collaboration and coordination, communication, government and legal matters, the planning process, and stakeholders. Further research is recommended to determine the necessity of having an institution for coordination to assist with planning in a transboundary basin.

Quantifying and modeling stream-aquifier interactions in the Elkhorn River Basin, Nebraska - Can Liu

  • Thesis Defense
  • 3/21/2014

This study combined statistical analyses, field investigations and numerical groundwater flow modeling to quantify the connectivity between the Elkhorn River and its adjacent aquifers in Nebraska. Non-parametric tests were conducted to detect increasing or decreasing tendencies of the time series of streamflow data from the Elkhorn River Basin. Investigation of streambed hydraulic properties was performed in the Elkhorn River near the town of Winslow and Norfolk, including in-situ permeameter tests on the streambed, sediment coring and electrical conductivity logging, and in-lab permeameter tests of sediment cores. Two numerical groundwater flow models were developed near the Atkinson and Winslow sites using MODFLOW-2005, the Atkinson model in the Upper Elkhorn River and the Winslow model in the Lower Elkhorn River. The aquifer system in each model was divided into five hydrostratigraphic units and external hydrologic stresses were also incorporated in the models. After model calibration, hypothetical wells having different locations, pumping schedules and screen depths were placed along the river in the model to simulate stream depletion. The results suggested that a well which was located more close to the river with shallow screen was more susceptible in causing stream depletion within the Atkinson model. The thick layer of silt/clay/till deposits in the Winslow area may reduce the hydrological connection between the river and aquifers and result in low and steady stream depletion rate. The all year pumping simulation of the two models could be useful in determining the "10/50" area for registered well regulation. Well configuration and hydraulic properties of the aquifer system had a significant impact on stream depletion in the study areas.

New statistical methods for analysis of historical data from wildlife populations - Trevor Hefley

  • Dissertation Defense
  • 3/21/2014

Wildlife biologists, many times with the help of ordinary citizens, have developed and maintained long-term data sets while monitoring the status of wildlife populations. These data sets can range from a collection of citizen reported sightings of a rare species to data collected by biologists using standardized methods. The commonality is that these data sets span a temporal and spatial scale that is beyond the scope of most scientic studies. Statistical methods are the main data analysis technique used for developing quantitative predictions in the life sciences, but these methods are poorly developed and rarely applied to long-term data sets. This underdevelopment of statistical methods and applications was the motivation for my research. I will present new statistical methods for time series analysis and spatial point processes. I apply these new methods to three different historical data sets from a population of bobwhite quail (1965-2011) and whooping cranes (1943-2012). My main results include detection of an extinction threshold and a predictive species distribution model that can be used to inform management actions.

Influence of non-native trout on native non-game fish in Nebraska headwater streams - Kelly Turek

  • Thesis Defense
  • 3/19/2014

Introduced, non-native trout may have detrimental competitive or predatory interactions with native fishes. However, few studies have experimentally examined interactions between introduced trout and native non-game species. The objectives of this study were to determine 1) if non-native rainbow trout Oncorhynchus mykiss influence survival, behavior, movement, or distribution of native longnose dace Rhinichthys cataractae under laboratory conditions, 2) if non-native rainbow trout influence survival of native longnose dace under in-situ conditions using in-stream enclosures, and 3) if non-native brown trout Salmo trutta or rainbow trout influence native populations or communities under natural conditions. Rainbow trout preyed on longnose dace at low rates in both laboratory and in-stream enclosure experiments suggesting that if rainbow trout and longnose dace overlap in microhabitat use, some predation is likely to occur. Therefore, it is not recommended that non-native trout be stocked in streams containing at-risk species. Greater non-native trout abundances resulted in greater distinction in native community composition and structure between sites with trout compared to sites without trout suggesting there may be increased risk to native communities in sites with high abundances of trout. Therefore, caution should be taken in stocking non-native trout even in streams with common and abundant native species.

Simulation of Meteorological Fields for Icing Applications at the Summit of Mount Washington - Sandra Jones

  • Thesis Defense
  • 2/14/2014

Hazards related to in-cloud icing on aircraft and ground structures are important considerations for structural design, risk mitigation and operations. A variety of robust ice accretion algorithms exist for application dependent purposes; however, these algorithms are often dependent on reliable meteorological input data to be of use. This study investigates the potential for predicting meteorological parameters relevant to in-cloud icing episodes at ground level using the Weather Research and Forecasting (WRF) model. Model performance with regards to explicit simulation of super-cooled cloud liquid water content, cloud droplet diameter, temperature, and wind speed is evaluated against measurements collected at the summit of Mount Washington. Simulation sensitivity to horizontal grid resolution, cloud microphysics parameterization, and terrain height representation are also discussed. Results from the case studies analyzed provide guidance for model configuration for icing purposes and justification for further scientific investigation.

Response of Large River Fishes to a Prolonged High Water Event in the Missouri River, Nebraksa - Nicholas Hogberg

  • Thesis Defense
  • 1/10/2014

The flow regime of many large rivers includes annual periods of floodplain inundation, and flooding is believed to be important to several components of large river ecology. Flow regulation in the Missouri River, Nebraska has homogenized its historically-dynamic flow regime and reduced access to off-channel habitat for several decades. Precipitation events during the winter and spring 2010-2011 caused the Missouri River to inundate its floodplain from late spring through early autumn. The objectives of this study were to 1.) compare fish community composition and structure on the floodplain at five sites on the Missouri River, Nebraska, 2.) compare flathead catfish trophic ecology during the flood in 2011 and non-flood in 2012, and 3.) predict age-0 channel catfish growth rate in the Missouri River using environmental data. Fish communities only differed between distant sites, and between one middle site and the remaining sites. Flathead catfish showed differences in stomach fullness, frequency of empty stomachs, and condition between years. Diet contents differed between years among individuals primarily consuming invertebrates, but were similar among individuals primarily consuming fish. The best model to predict age-0 channel catfish growth rate incorporated growing season duration and low discharge duration. The results of this study suggest that fish respond to environmental conditions in regulated rivers. Future research will add to our understanding of fish response to hydrological conditions and help guide water management in regulated rivers.

Accuracy or Precision: Implications of Sample Design and Methodology on Abudance Estimation - Lucas Kowalewski

  • Thesis Defense
  • 12/17/2013

Estimation of population size by spatially replicated counts (point-count method) has been used for many large-scale animal-monitoring programs, yet its application in aquatic environments has been limited. Design of sampling scenarios for point-count population-estimate surveys can influence the accuracy and precision of the population estimate. The first objective of this study was to examine how different sampling scenarios, given interaction with environmental factors, influence accuracy and precision of population estimates derived from the point-count method. In general, across the sampling scenarios combined with environmental factors evaluated, a trade-off exists between accuracy and precision of population estimates. The second objective of this study was to evaluate the applicability of the point-count population estimation method within an aquatic environment. Spatial modeling allowed by this method provides an advantage over other population estimation methods, by providing a link to the relationship of abundance, detection, and habitat use.

Forecasting the Invasion Risk of Non-Native Plant Species with the Nebraska I-Rank Assessment - Justin Williams

  • Thesis Defense
  • 12/16/2013

The objective of my research is to determine the invasion potential of non-native plant species in Nebraska. I utilized the Impact Rank Risk Assessment Framework (or I-Rank) to evaluate 56 non-native plant species. The I-Rank framework is an assessment designed to evaluate and rank the threat of invasive plants species based on their impact on native species and ecosystems, distribution and abundance, and management difficulty. The I-Rank framework provides a method to objectively evaluate potential invasive species and can be customized for specific areas and circumstances. I used information from herbaria collections, agency reports, literature review, online databases, and solicited expert opinion to evaluate each species. I present methods for quantifying sources of uncertainty in the I-Rank scores. My results indicate the I-Rank Risk Assessment Framework provides a straightforward method for evaluating and identifying invasive species threats and is a valuable tool to synthesize information from numerous sources to prioritize species for management decisions. I discuss relative strengths/weaknesses of the method, offer conclusions, and make suggestions for future research.

"We Shall Meet Beyond the River": An Analysis of the Deathscape of Brownville, Nebraska - Ashley Barnett

  • Dissertation Defense
  • 12/2/2013

Gravestone studies have traditionally focused on the East Coast, particularly the Northeast, because of the long Euro-American settlement history in that region and because of a landmark 1966 study produced by Edwin Dethlefsen and James Deetz which focused on this region. Significantly less attention has been paid to the interior of the continent, particularly the Great Plains. This study analyzed the temporal variations in gravestone iconography and inscriptions to determine major cultural shifts that took place in Brownville, Nebraska, from the town's founding in 1854 to the present. All 1,229 gravestones in Walnut Grove Cemetery were recorded and analyzed for the presence of 104 iconographic motifs and 103 textual variables. Special attention was paid to variations in inscriptions and iconography with gender, as well as to spatial variation in gravestone location with race. Unlike previous studies, which focus primarily upon iconography, this dissertation provides an in-depth exploration of the language that appears on the gravestones in Walnut Grove Cemetery. Four iconographic phases and three or four textual phases were identified for this cemetery, and both the iconographic and temporal phases showed significant temporal overlap. The onset of each phase was shown to correspond temporally to a significant shift in the social settings of Brownville. Major changes in concepts of gender and theology in Brownville were identified and explanations are offered for these shifts. African-American and Native American interments in Walnut Grove proved difficult to identify, suggesting the concept of subaltern invisibility may influence the material culture of this cemetery. This study shows that, while the material culture of Walnut Grove Cemetery was not effective for identifying the diversity of Brownville, it can be used to identify major shifts in theological thought, periods of social upheaval, and concepts of gender in this Nebraska river town.

Altitudinal and Thermal Variation in Ambient Nutrient Uptake and Uptake Kinetics in Temperature Streams - Brady Kohler

  • Thesis Defense
  • 12/2/2013

Temperature is often considered a master variable controlling many chemical reactions and biological processes. Some research efforts have begun to investigate how temperature effects nutrient uptake dynamcs, but little has been performed regarding nutrient uptake kinetics. In this study, we investigated 1) how amibent nutirent uptake rates and 2) nutrient uptake kinetics vary along a thermal gradient, created by strategically selecting streams at various altitudes. Instantaneous nutrient additions were performed at 15 streams within three adjacent drainage basins in the Colorado Rocky Mountains to test these questions. Ambient uptake metrics were estiamted using multiple approaches and examined against both instant temperatures and long-term thermal regimes. We found no relationship amoung nutrient uptake velocities and temperature. However, NH4+ uptake rates increased with temperature whereas NO3- uptake rates decreased with temperature, though the significance differed by estimation approach and duration of thermal regime. Response in uptake to increased nutrient availabilty was also estimated for each stream, where response in NO3- uptake was found to increase with increasing temperatures.

Anoxia tolerance of forensically important calliphorid species - Melissa Lein

  • Thesis Defense
  • 11/22/2013

n/a

Determining Scaphirhynchus Population Demographics and Dynamics: Implications for Range-Wide Management, Recovery, and Conservation - Marty Hamel

  • Dissertation Defense
  • 11/22/2013

Sturgeons (Acipenseridae) have experienced world-wide declines as a result of anthropogenic effects such as over-harvest, habitat degradation, altered flow regimes, and pollution. Nearly all European and Asian sturgeon species have experienced population declines and have subsequently been classified as either threatened or endangered. North American sturgeons have experienced a similar plight in that all eight native sturgeon species are listed as endangered, threatened, or of special concern. Direct linkages between North American sturgeon declines and anthropogenic effects are difficult to assess due to scale considerations, fluctuating environmental conditions, difficulty in capture, and the interaction of all these effects. To recover, restore, or maintain abundance of these species across their range, thorough knowledge of life history characteristics or strategies, population dynamics, and population connectivity for each species is imperative. In this dissertation, I use data from local (Platte and Missouri Rivers, Nebraska) to nearly range-wide scales to describe components of Scaphirhynchus sturgeon population dynamics and demographics and assess various analyses typically used for calculation of dynamic rate functions.

Spatial and Temporal Participation in Recreational Fishing - Dustin Martin

  • Dissertation Defense
  • 11/21/2013

Buffering inland fisheries against large-scale changes in ecosystem function, climate regimes, and societal-resource valuations requires progressive management approaches that incorporate fish and angler dynamics at large spatial and temporal scales. In this dissertation, I used three techniques to describe angler behavior in a region (19 reservoirs) during a 4-year period. I provided a means to evaluate fishing effort on individual-waterbody and regional scales from posts to an online fishing social network; this would potentially reduce the need for intensive creel surveys. I used kernel-density estimation to describe the spatial area of influence of reservoirs; differences in area of influence are likely related to access and amenities, fish community, and angler preferences. Finally, network analysis provided a social-ecological perspective to angler behavior and an explicit link between anglers and the reservoirs that they chose to fish. In combination, these techniques provide natural resource agencies with the tools needed to further fisheries management and ensure the resiliency and sustainability of inland recreational fishing.

Recruitment of Walleye and White Bass in Southwest Nebraska Irrigation Reservoirs - Jason DeBoer

  • Thesis Defense
  • 11/14/2013

Walleye Sander vitreus and white bass Morone chrysops are among the most popular sportfish in the reservoirs of the Great Plains. Despite considerable effort by the Nebraska Game and Parks Commission stocking walleye and managing reservoirs for walleye and white bass, populations of walleye and white bass in southwest Nebraska reservoirs are dynamic, as erratic recruitment has led to "boom and bust" fisheries for these two species. We investigated timing of and factors regulating recruitment using several approaches. We found no correlation between larval or age-0 juvenile fish abundances and age-1 fish abundance for either walleye or white bass. The variables in the candidate model sets for walleye were most-often related to water-level drawdown. The variables in the candidate model sets for white bass were most-often related to adult white bass abundance and condition, and to factors affecting over-winter mortality of juvenile white bass.

The Influence of Regulations on Duck Hunters and Harvest - Matthew Haugen

  • Thesis Defense
  • 11/12/2013

Although regulations, duck hunters, and duck harvest are interconnected, the relationships among them have not been fully explored. I used U.S. Fish and Wildlife Service's Parts Collection Survey to examine both duck harvest and duck hunter behaviors with regards to regulations in the Central Flyway. I first examined what factors best explained the daily variation in harvest distribution across the hunting season for mallards (Anas platyrhynchos), dabbling ducks (Anas spp.), and diving ducks (Aythya spp.). Secondly, I examined how hunter behaviors were influenced by harvest regulations. Finally, I documented co-occurrence of duck species in the daily bags of hunters, and developed models to predict the effects of daily bag limit changes on both target and non-target species. I found regulation changes may influence the spatial harvest of both dabbling and diving ducks, whereas the distribution of mallard harvest appeared to be influenced more by hunting pressure, water on the landscape, and mallard density. Regulations also influenced select measures of duck hunter behavior (e.g., average daily bag, gender selectivity of mallards). However, regulations did not differentially affect most duck hunters for the measures of behavior I examined. Co-occurrence results provided insight into the harvest relationships between pairs of ducks species (e.g., redhead [A. americana] were likely harvested with canvasback [A. valisineria]). Co-occurrence relationships allow managers to consider the effects regulatory changes have on non-target species, an important consideration given the aggregate nature of duck harvest. Ducks receive considerable attention from managers in North America, and the Parts Collection Survey contains information that should provide managers with tools and inferences for waterfowl management which account for relationships among regulations, duck hunters, and duck harvest.

Influences of Population Attributes on the Sustainability of Walleye Populations - Robert Kill

  • Thesis Defense
  • 8/29/2013

n/a

Improving Time Structure Pattern of Orthogonal Markov Chain and its Consequences in Hydraulic Simulations - Juan Jaimes Correa

  • Thesis Defense
  • 8/19/2013

n/a

Analysis of Urban Consumptive Water Use, Case Study in City of Lincoln - Yao Li

  • Thesis Defense
  • 8/10/2013

The trends of increasing water demand and drought occurrences in Nebraska’s urban areas pose a new crucial issue to water resource management. Former studies in Nebraska mainly focused on rural water demand caused by intensive agricultural irrigation, while largely ignoring the growing municipal water use. Therefore, this thesis aims to investigate total water use and consumptive water use in three major urban land use categories of residential, CIO (commercial, industrial and others), and open space. Three case cities are City of Lincoln, Grand Island and Sidney. First, a reliable and feasible methodology of estimating consumptive water use is developed based on the analysis of end water use activities. Then, possible influential factors (e.g. population, total landscape area) are statistically examined to evaluate their effects on the amount of total and consumptive water use. Afterwards, quantity classification and spatial autocorrelation analyses are used to visually assess and quantify the spatial patterns of total and consumptive water use at the census block level, 2010. In the three case cities, residential consumptive water use varies from 31% to 57% of total water use, and positive relationships with precipitation and aridity are identified. CIO consumptive water use percentage ranges from 19% to 27%. Open space consumptive water use is nearly equal to the open space total water use. Census block level linear models are identified between influential factors and amount of water use, which has been rarely applied by previous research. First, the best predictors of residential total water use area population and total landscape area in three case cities. A positive correlation between residential consumptive water use and total landscape area is identified in the Sidney while similar relationship is not found in the other two cities. Second, there is no linear regression relationship identified between CIO total water use/consumptive water use and available independent variables in this study. Third, both open space total water use and consumptive water use can be positively related to total landscape area. Spatially, high water use blocks are commonly clustered in suburban areas with larger lots and lower population densities. Low water use blocks are commonly located near downtown living areas with less yard area and higher population densities. Overall, the methodology and statistical outcome can improve the understanding of urban water supplies and uses in dissimilar urban areas across Nebraska, providing foundation for further urban water studies and integrated water management.

Shovelnose Sturgeon Reproductive Ecology in the Lower Platte River, Missouri - Matt Rugg

  • Thesis Defense
  • 7/26/2013

n/a

Exploitation of Channel Catfish in Nebraska Flood-Control Reservoirs - Chris Wiley

  • Thesis Defense
  • 7/22/2013

n/a

Remote Sensing of Green Leaf Area Index in Maize and Soybean: Spectral Behavior and Algorithm Development from Close-Range to Satellite - Anthony Nguy-Robertson

  • Dissertation Defense
  • 7/16/2013

One of the most commonly utilized vegetation biophysical characteristics is leaf area index (LAI) due to its wide applicability. There is an interest to remotely detect the green (photosynthetically active) LAI. Remote sensing systems have been successful for determining both phenology and estimating green LAI. This dissertation seeks to confirm these earlier findings using close range remote sensing techniques that have higher spatial and/or temporal resolution and to explore alternative methodologies for improving estimation accuracy. Specifically this research [1] developed an approach for creating a Moderate Resolution Imaging Spectroradiometer (MODIS) high spatial resolution product for estimating green LAI on the base of data collected using close-range sensors. It was determined that the vegetation indices (VIs) wide dynamic range vegetation index (WDRVI) and enhanced vegetation index 2 (EVI2) were capable of accurate estimation of green LAI from MODIS 250 m data. [2] Explored a new approach for maximizing the sensitivity of VIs to green LAI. Rather than use one VI, we suggested using multiple VIs in different dynamic ranges. Thus, the sensitivity of the VI to the green LAI was preserved and simpler linear models could be used instead of complex non-linear ones. Two combined vegetation indices were presented using near infrared and either the red or red edge bands. While the red band is more common in sensors, the red edge band was found to be species independent for maize and soybean. The two species-independent VIs were red edge normalized difference index (Red Edge NDVI) and red edge chlorophyll index (CIred edge). [3] Algorithms were developed for estimating green LAI in four vastly different crops (maize, potato, soybean, and wheat) that do not require re-parameterization. The most promising VIs for developing a unified algorithm utilized either a green or red edge bands. [4] Determined that, in addition to traditionally used vegetation indices (VIs), the 2-D spectral spaces (e.g. red vs. green reflectance) were capable of identifying four distinct stages in phenology (e.g. soil/residue, green-up, vegetative, and senescence). Overall, this research suggests that close-range sensors were a practical alternative to using satellite-based data exclusively.

Avian Vocalizations During the Winter Change in Response to High Levels of Traffic Noise - Amy Oden (Larson)

  • Thesis Defense
  • 7/9/2013

Low frequency traffic noise may cause acoustic masking of avian vocalizations. This constant background noise may cause birds to shift or otherwise alter the frequencies of their vocalizations in order to be heard. During the winters of 2011-2012 and 2012-2013, we recorded and measured the "chick-a-dee" vocalization of Black-capped Chickadees (Poecile atricapillus) and the "po-ta-to-chip" vocalization of American Goldfinches (Spinus tristis) to determine if bird vocalizations near high traffic noise had higher minimum and maximum frequencies than bird vocalizations near low traffic noise. We found that both the Black-capped Chickadee and American Goldfinch vocalizations have a higher minimum frequency near high traffic noise while the maximum frequency showed no change. This suggests that these species will alter the part of their vocalization that is acoustically masked by traffic noise in order to better transmit the vocalization. However, changing parts of a vocalization may result in a poorer vocal performance or the message in the vocalization being received incorrectly, both of which could cause harm to the sender and the receiver.

Decomposition Rates and Nutrient Release of Different Cover Crops in Organic Farm Systems - Jian-ru Shi

  • Thesis Defense
  • 6/28/2013

n/a

Microbial Ecology, Nitrogen, and Nitrous Oxide Trends in Marginal Soils Used for Cellulosic Biofuel Production in Eastern Nebraska - Carla Ahlschwede

  • Thesis Defense
  • 5/31/2013

n/a

Exploring the Nature of Space for Human Behavior in Ordinary Structured Environments - Molly Cannon

  • Dissertation Defense
  • 4/19/2013

What is the nature of the built environment? Built environments are the settings within which people carry out activities and emerge from the specific combining of spatial conditions with specific social content for the setting. The social content and the spatial conditions form a core-defining relationship that serves to distinguish one structured setting from another. A core-defining relationship such as this refers to the essence of the built environment. What are the implications for human behavior that emerge from conceptualizing built environments in this manner? I argue that space, through its essential relationship with the contexts of daily living (i.e. social content), qualifies, or transforms how environmental information of those conditions appear. In order to interpret and recognize inherent meaning within those spatial conditions, people rely on a shared set of cultural norms and expectations concerning the built environment. Should the relationship between the social content of a setting and the spatial conditions that structure a setting be disrupted or misunderstood, users of the setting will have difficulty interpreting and carrying out their intended activities. To test this assumption, the case study assessed participants' evaluations of images of ordinary settings in two presentations, first where the spatial conditions remained unaltered and second where the spatial conditions were disrupted in a random non-meaningful manner. A content analysis was employed to generalize participant narratives and provide necessary data to perform a two-factor analysis that assessed the potential for groupings among participants' evaluation of the images. Results of the study suggest that people rely on spatial conditions for interpreting built environments in their consideration for the potential to carryout activities and social engagements. When spatial conditions are lacking or meaningless, participants express frustration and confusion and are unable to articulate how they might engage in social activity within the image. Further, the study illustrates that the social-spatial core relationship is a necessary component in the environmental knowing process for built environments.

Amphibian Occupancy and Functional Connectivity of Restored Wetlands in the Missouri River Floodplain - Michelle Hellman

  • Thesis Defense
  • 4/18/2013

Wetlands are among the most degraded habitats in the world. Wetland decline may threaten many taxa including shorebirds, amphibians, and fish. As agencies increase restoration of wetland habitat, monitoring is crucial to inform and improve the process. Permeable skin sensitive to water quality and biphasic life histories requiring both terrestrial and aquatic habitat make amphibians good indicators of wetland health. I modeled amphibian occupancy in restored Missouri River bends to determine habitat characteristics associated with the presence of amphibians. Landscape characteristics, like connectivity of wetlands, facilitate between-patch dispersal and may be just as important to the local persistence of amphibians. I assessed connectivity for anurans of wetlands within a bend and recommend locations for new restorations that can improve connectivity of the bend.

Discriminating Tillage Practices using Landsat-5 Thematic Mapper - Sonisa Sharma

  • Thesis Defense
  • 4/12/2013

Tillage management practices are an important component to crop production and to federal and state conservation efforts and crop subsidy programs. Crop residue created by conservation tillage reduces soil erosion and reduce evaporation from exposed soil. Agro-hydrological models require information on tillage practices to estimate their impacts on soil-water-holding capacity, total evapotranspiration, carbon sequestration, water runoff and water and wind erosion for agricultural lands. Classification of tillage practices using remote sensing offers promise for the rapid collection of tillage information on individual fields over large areas. Using satellite imagery proves to be challenging due to the similarity in spectral signatures for soils and crop residues and the typically broad spectral bands used by moderate resolution satellites needed to cover large areas and with frequent revisit time. In this study, Landsat 5 Thematic Mapper images in years 2008 and 2009 acquired over southeastern Nebraska (NE) were used to discriminate tillage practices using a Quadratic Discriminant Analysis (QDA) approach. Ground truth data regarding the presence or absence of no-till practices were collected by the US Department of Agriculture-Natural Resources and Conservation Service (USD-NRCS) at 31 locations in Adam and Fillmore Counties. Results indicated that Landsat-TM bands 1, 3, 4, 5 and 7 classified 75-91% correctly for no-till and 20-55% for till in March and May of 2008 and 2009 respectively. Similarly, the Landsat based tillage indices such as simple tillage index, normalized difference tillage index, and normalized difference of Bands 1 and 5 discriminated tillage practices in March and May of 2008 and 2009 images with 81-91% for no-till and 12-26% for till respectively. The QDA approach with Landsat 5 data appears to be efficient and effective in classifying tillage practices over large areas.

Building Upon Common-Pool Resource Theory to Explore success in Transitioning Water Mangement Institutions - Christina Hoffman

  • Dissertation Defense
  • 4/2/2013

Nebraska, like many regions around the world, is faced with the challenge of adapting to a new era in water management. Increasing demands for water resources, mounting concerns over threatened and endangered species, and obligations to abide by interstate water allocation agreements have motivated Nebraska to revisit traditional water management approaches. However, while Nebraska's water management institutions have undergone significant change, little research exists on the influence these changes have had on the ability of water institutions to successfully manage water allocations. This research study builds upon established principles for successful common-pool resource management through both qualitative and quantitative exploration to gain robust insight into how Nebraska's current water management system is working, as seen by stakeholders. Improving resource managers' ability to learn about and better understand the implications of management approaches and policies can lead to more successful water resource institutions.

Removing PAHs from Runoff Water by Combining Ozonation, Adsorption, and Biodegradation - Chainarong Sakulthaew

  • Dissertation Defense
  • 3/19/2013

The water quality of lakes and rivers associated with metropolitan areas is declining from increased inputs of urban runoff that contain polycyclic aromatic hydrocarbons (PAHs). Our objective was to develop a treatment technology that removes PAHs from urban runoff. We accomplished this by developing a flow-through system that uses ozone (O3) to quickly transform PAHs in a runoff stream and then removes the O3-transformed PAHs via adsorption to either activated carbon or carbon nano-onions (CNOs); adsorbed PAH products are then further biodegraded. To quantify the efficacy of this approach, 14C-labeled phenanthrene and benzo(a)pyrene, as well as a mixture of 16 PAHs were used as test compounds. These PAHs were pumped from a reservoir into a flow-through reactor that continuously ozonated the solution. Outflow from the reactor then went to a chamber that contained either activated carbon or CNOs that adsorbed the O3-treated PAHs and allow clean water to pass. By adding a microbial consortium to the CNOs following adsorption, we observed that bacteria were able to degrade the adsorbed products and release more soluble, transformed products back into solution. Control treatments confirmed that parent PAH structures were not biologically degraded following CNO adsorption and that O3-treated PAHs were not released from the CNO in the absence of bacteria. For phenanthrene, we identified diphenaldehyde as the product of ozonation and diphenaldehydehdric acid as the biological product released from the CNOs. We then compared the biodegradability of these products to the parent structures in unsaturated soil microcosms. Results showed that the parent phenanthrene structure was more biodegradable (∑14CO2 released = 51%) than the transformed products (34.5 - 36.7%) but for the 5-ring benzo(a)pyrene, the products produced by ozone (22.3%) or released from the CNO following biological treatment (35.2%) were significantly more biodegradable than the parent compound (2.7%). As an alternative to using activated carbon or CNOs, we also verified that the ozonated product (diphenyldehyde) could be biologically mineralized in a bioreactor and that mineralization rates improved with acclimation of the microbial population. These results support the combined use of ozone and biological degradation as a means of removing PAHs from urban runoff.

New Tools for Quantitative Decision Analysis in Applied Ecology and Conservation - Adam Schapaugh

  • Dissertation Defense
  • 3/11/2013

Scientists have generated a massive body of theory aimed at predicting and managing the impacts of anthropogenic activities on populations, species, and ecosystems. Transforming this research into knowledge that informs complex decision-making problems remains a major challenge in environmental management and conservation. My dissertation research aims to address this issue through the development and application of mathematical and statistical models. I integrate tools, concepts, and techniques from ecology, applied mathematics, computer science, and statistics to build structured decision-making frameworks for spatial prioritization, resource allocation, and optimal scheduling. I also tackle several of the technical challenges limiting the utility of such tools in practice, and seek to make them accessible to other scientists and decision-makers. Much of my research is motivated by the interest in land acquisition as an in situ conservation strategy. In Chapters 1 and 2, I develop an integrated reserve selection framework for spatial priority-setting and optimal investing. The framework combines Bayesian methods and Markov decision theory in the context of making land acquisition decisions. A second focus of my research focuses on overcoming several of the technical and computational challenges of utilizing Markov decision processes (MDPs) in the context of real-world planning. In Chapter 3, I introduce and test and class of approximation algorithms developed in the artificial intelligence community to simply and solve MDPs with large state spaces. In Chapter 4, I develop a novel method that uses information-gap (radius of stability-type) models to represent uncertainty in the state transition function of an MDP. Rather than requiring information about the extent of parametric uncertainty at the outset, this method addresses the question of how much uncertainty is permissible before the optimal policy would change. Finally, in Chapter 5, I develop a pair of sensitivity metrics for info-gap decision analysis. Both sensitivity metrics are an essential addition to the robust optimization toolkit, providing a systematic approach for identifying weaknesses in an info-gap decision analysis. They are also needed quantities in the effort to make sound, defensible decisions.

Collaboration Between Traditional and Biomedical Practitioners in the BUI Division, Cameroon - Mary Hallin

  • Dissertation Defense
  • 3/8/2013

This dissertation examines collaboration between traditional and biomedical practitioners in the Bui Division in the North West Region of Cameroon, Africa. The literature on collaboration tends to examine the differences rather than the similarities between traditional and biomedical practitioners. Studies rarely compare their attitudes on collaboration or ways to bring the two groups together. This dissertation fills these voids. Using qualitative and quantitative methods, I examine the attitudes of traditional and biomedical practitioners concerning collaboration and identify potential ways to bring the two practitioner groups together.

Cholera, HIV/AIDS, tuberculosis, and a shortage of biomedical personnel are challenges facing Cameroon and other African countries. Traditional doctors could be tapped to meet these health care needs. The ratio of traditional doctors to biomedical doctors is around 100:1. Approximately 80% of the population in Africa and Cameroon use traditional medicine often simultaneously with biomedicine. In the 1970s, the World Health Organization (WHO) advocated collaboration with traditional practitioners in providing primary health care, yet biomedical and traditional practitioners continue to work independently.

From August 2008-January 2009, I conducted interviews with 36 biomedical practitioners and 56 traditional practitioners in the Bui Division. I studied the relationships of the following variables on the collaborative process: 1) distance to a hospital, 2) personal religious affiliation, and 3) religious orientation of the health care facility. This study found that 1) biomedical and traditional practitioners support collaboration, and 2) personal experience with a traditional doctor and personal religious affiliation may influence a biomedical practitioner’s attitude toward collaboration. The main form of interaction between the two groups was referrals -- more traditional practitioners than biomedical practitioners referred patients to the other sector.

Both groups suggest that a face-to-face meeting would kick start the collaborative process. The following are proposed as effective facilitators of the collaborative process: 1) somebody familiar with both practitioner groups, and 2) a government representative. Building a sustainable collaborative relationship between traditional and biomedical practitioners could lead to improved health care delivery in the Bui Division and throughout Africa.

Proximal Sensing as a Means of Characterizing Phragmites Australis - Travis Yeik

  • Thesis Defense
  • 2/8/2013

Phragmites australis is an invasive wetland weeds found throughout much of the United States. Monitoring the growth and spread of this emergent macrophyte can be an important step in developing and implementing successful management strategies. Monitoring the morphology of a vegetation species with a sensor capable of hyperspectral resolution, and at close proximity to the canopy of interest, is often a first step necessary for understanding the basic species-specific reflectance and for quantifying the manner in which light interacts with the plants comprising the community. Upon completion of the 2011 field season and during the analysis of acquired Phragmites spectra, inconsistencies were noted in the reflectance profiles. In an effort to avoid loss of important data, a procedure was developed in order to correct erroneous data with ancillary data collected concurrently with the hyperspectral data. Further research was aimed at characterizing the spectral responses of a Phragmites canopy over the course of an entire growing season, and then relating the acquired reflectance data to four primary stages in the phenological cycle by means of estimating vegetative fraction over the canopy. A new vegetation index, termed the "Albedo Corrected Vegetation Index" (ACVI) was developed and tested as a means of increasing the accuracy in estimating vegetation fraction. Finally, seed production and shoot density, both of which are closely linked with the invasive characteristics of Phragmites are estimated using a simple digital camera and a more sophisticated approach using dual spectroradiometers. The findings of this thesis research will demonstrate the potential utility of monitoring invasive Phragmites by means of sensors operating in close proximity to the canopies.

Winter Ecology of Sandhill Cranes (Grus canadensis) in Northern Mexico - Ingrid Barcelo

  • Dissertation Defense
  • 12/14/2012

n/a

The use of tree rings to study the impacts of stream flow and climate variability on native and invasive woody species along a semi-arid riparian ecosystem in the Great Plains - Kristen Skolaut

  • Thesis Defense
  • 11/28/2012

Forested riparian areas of the Northern Great Plains have historically been dominated by the native Populus deltoides L. vegetation type. Changes in climate, stream flow, groundwater, and management practices in the past few decades have promoted the expansion of the upland native woody species Populus deltoides L. and the invasion of the non-native Elaeagnus angustifolia L. into these riparian ecosystems. This study aims at using dendrochronology, or the study of tree rings, to assess the impacts of intra- and inter- annual climatic variability and stream flow over the past decades, on the annual tree ring growth, oxygen and carbon isotopic signatures, and performance of native and invasive woody species in a riparian ecosystem along the Republican River in Nebraska.

Tree ring analysis showed that P. deltoids and J. virginiana growth displayed a greater dependency on climatic factors than E. angustifolia. Populus deltoids growth was significantly dependent on previous year summer temperatures, and on annual stream flow, and Juniperus virginiana growth showed a significant dependency on the previous growing-season precipitation and on annual stream flow. On the other hand, E. angustifolia growth was negatively correlated with annual stream flow and the species displayed the least growth response to climate variability.

Oxygen and carbon isotopic ratios (δ 13O and δ 18C, respectively) of tree rings indicated that water use efficiency (WUE) in J. virginiana was significantly greater and showed the most response (i.e., increased) under stressful environmental conditions compared to the other two species. Water use efficiency in P. deltoids showed little dependency on climate variability and/or water availability. Results show that the three species followed different strategies to co-op with environmental stresses. The significance of these results and their consequence on the ecology of the ecosystem will be discussed.

Population Characteristics, Development of a Predictive Population Viability Model, and Catch Dynamics for Pallid Sturgeon in the Lower Missouri River - Kirk Steffensen

  • Thesis Defense
  • 11/26/2012

Population characteristics and long-term population trends of pallid sturgeon Scaphirhynchus albus in the lower Missouri River are relatively unknown. As recovery efforts continue, understanding and quantifying these characteristics and trends are critical for species recovery and future management decisions. Therefore, the objectives of this study were to determine the pallid sturgeon population characteristics, predict changes to the pallid sturgeon population based on different management and life history scenarios, and examine trot line catch dynamics in the lower Missouri River. Catch rates for pallid sturgeon collected with gill nets did not significantly change while catch rates using trot lines significantly declined for wild pallid sturgeon (P=0.0001) but did not differ among years for hatchery-reared fish (P=0.0610). The proportion of reproductively ready females to non-reproductively ready females was 1:2.0, compared to the male ratio of 1:0.9. The minimum female length-at-maturity was 788 mm and 798 mm for males while the minimum age-at-maturity for known aged hatchery-reared fish was age-9 for females and age-7 for males. The mean relative fecundity was 7%. Our population viability model was most sensitive to =age-1 survival rates. Fluctuating female spawning frequency by one year had minimal effect on the overall population growth and age-at-maturity was less sensitive than spawning frequency. Catch per unit effort was 14.6 fish per trot line rigged with hook timers to study the catch dynamics; however, several hook timers were activated but did not capture a fish. Therefore, the corrected CPUE was 17.7 fish per line with over half of the hook timer activations occurring 4-h post-deployment. Detecting shifts in population characteristics is essential for understanding population dynamics as hatchery inputs and natural perturbations continue to change the population structure. Barring any unforeseen natural catastrophes, the pallid sturgeon population in the lower Missouri River is not in immediate danger of local extirpation; however, the population appears to be a far from viable nor self-sustaining.

Flow Regime, Guppy Introduction and Light Manipulation Influence Invertebrate Assemblages in Trinidadian Streams - Tom Heatherly

  • Dissertation Defense
  • 11/13/2012

This dissertation concerns natural and experimental influences on macroinvertebrate assemblage structure and stoichiometry in Trinidadian streams as well as a new data analysis protocol for the bioassessment of rivers and streams of Nebraska. In the second chapter, I present models that describe how aspects of the natural flow regime, especially flood frequency and recovery time, structure individual invertebrates as well as overall assemblage structure. Chapter 3 describes the influences of light manipulation and the introduction of guppies on macroinvertebrates. I describe the influences of phylogeny, allometry and environment on the C:N:P stoichiometry of Trinidadian invertebrates in Chapter 4. Finally, I present a data analysis protocol for assessing the biotic integrity of Nebraska's streams and rivers that uses physical factors to compare ecologically similar systems. I found that almost all invertebrates in montane Trinidadian streams are predictable by flow regime, and that a sizeable number of invertebrates as well as diversity respond positively to hydrologic variability. I also found that increased light immediately and persistently stimulated invertebrate assemblages, and that large increases have the capability of stimulating multiple trophic levels and feeding groups. Guppies significantly reduced the abundance of invertebrates, but only after they had been introduced for two years. Phylogeny explained most of the variance in invertebrate stoichiometry, but allometric relationships were common and the stream sampled often explained as much variance as allometry. I also found widespread variation in carbon and nitrogen content, which contradicts previous findings of homeostasis of consumers for these elements. Finally, I found that stream size and temperature were the primary factors responsible for different assemblages in Nebraska reference streams. Utilizing stream size and temperature to compare test sites to reference conditions proved to be more realistic than using proximity-based ecoregional groupings. My results elucidated the important effects of flow and top down and bottom controls over invertebrates in Neotropical streams, and found a surprising amount of variability in the stoichiometry of these consumers. The application of ecological theory to bioassessment should also ensure that the streams and rivers of Nebraska are managed properly.

Improving the Treatment of Pure an dAqueous-Phase TCE in Low Permeable Zones with Permanganate - Chanat Chokejaroenrat

  • Dissertation Defense
  • 11/9/2012

Treating pure and dissolved-phase trichloroethene (TCE) in the low permeable zones (LPZs) of contaminated aquifers is a particularly challenging issue for injection-based remedial treatments. This is because injected oxidants typically stay in the more porous zones of an aquifer and bypass LPZs. Once the porous zones surrounding a LPZ are treated, contaminants diffuse out of the LPZ and contaminate flowing water, a process known as rebound. When permanganate (MnO4 -) is used as the chemical oxidant, the three hurdles to reducing rebound include: getting the MnO4 - to penetrate the LPAx, minimizing the MnO2 rind formation, and overcoming the kinetic constratins of treating a DNAPL with an aqueous-phase oxidant. Our objective was to improve the sweeping efficiency of permanganate into LPZs to treat TCE. This was accomplished by conducting 2D transport experiments that quanitfied the ability of MnO4- to penetrate and sweep through a LPZ that was spiked with either pure or dissolved-phase 14C-TCE. The remedial treatments evaluated included parting MnO4- with: (i) a shear-thinning polymer (Xanthan); (ii) stabilization aids that minimized MnO2 formation, and (iii) a phase-transfer catalyst. In addition, we quantified the ability of these flooding solutions to improve TCE destruction under batch conditions by developing miniature LPZ cylinders that were spiked with 14C-TCE. Transport experiments showed that MnO4- alone was inefficient in penetrating the LPZ and caused significant MnO2 rind formation when pure-phase TCE was present. By including xanthan with MnO4-, the sweeping efficiency increased significantly and the total percentage of disolved-phase TCE oxidation increased by 12% over MnO4- alone. Although xanthan improved dissolved-phase TCE oxidation, MnO2 rind formation was still evident when pure-phase TCE was present. By including xantan and the stabilization aid, sodium hexametaphosphate (SHMP) sweeping efficience was 100% and MnO2 precipitation in LPZ was minimal. By differentiating transport 14C-effluent into "TCE" versus "oxidized-TCE," results showed the MnO4- + xanthan + SHMP treatment oxidized 8% more pure-phase TCE than MnO4- along. Both experiments also confirmed that the stabilization aids tested improved TCE destruction by 12 to 20%. These results support the use of xanthan and stabilization aids in treating both pure and dissolved-phase TCE in contaminated aquifers.

Effects of Length Limits on Secually Size Dimorphic Fishes - Peter Spirk

  • Thesis Defense
  • 11/9/2012

Length limits are used by fishery managers as a method to alter size structure of fish populations. Unfortunately, biological differences between fish sexes (i.e., sexual-size dimorphism) may lead to sex-specific rates of recruitment, growth, and mortality. The addition of angler harvest to most aquatic systems likely accentuates differences in sex-specific rates by selectively harvesting the fastest-growing and largest fish from a population. The first objective of this study was to document the extent of sexual-size dimorphism for white bass and walleye at a Nebraska reservoir. Growth rates were similar between male and female white bass although male white bass were consistently shorter than their female counterparts at a given age. Male walleye grew slower and were consistently shorter than their female counterparts at a given age. The second objective was to document the size, sex, and age of white crappie, white bass and walleye harvested in two Nebraska reservoirs. Harvest was female biased for both white crappie and white bass, whereas harvest was similar for both male and female walleye. The third objective was to determine if size-, sex- or age-selective harvest was occurring for white bass and walleye at a Nebraska reservoir. Anglers harvested female white bass at a greater proportion than was sampled during NGPC annual population surveys. Anglers at Sherman Reservoir did selectively harvest female walleye based on size, although in contrast to the white bass population, sex-selective harvest was not apparent for walleye. The final objective was to provide a model that predicts possible outcomes from using different length limits for sexually size dimorphic fishes. Although there was a noticeable difference in the number of fish in a population for each length limit, the pressure applied to the population by catch-and-release mortality kept the sex ratio close to a 1:1.

STOPOVER DECISIONS OF MIGRATORY SHOREBIRDS: AN ASSESSMENT OF HABITAT USE, FOOD AVAILABILITY, BEHAVIOR AND PHENOLOGY - Ryan Stutzman

  • Thesis Defense
  • 11/8/2012

Habitat decisions have important implications to individual fitness as well as population dynamics and community structure. Understanding how changes to ecosystem structure and function impact species and populations of conservation concern is essential for conservation delivery to be effective. During 2010-2011, I examined how long-distance migratory shorebirds have responded to extensive, agriculturally-driven alteration to wetland habitats. I focused on a suite of ecological conditions that are expected to influence migrant fitness including habitat preference, resource availability and behavior. Additionally, because land use change is expected to act in conjunction with climate change to alter wetland habitats, I examined a number of phenologic variables and made predictions on how migrants might be affected in the future.

Migrant shorebirds were more likely to use highly-altered, agricultural wetlands and did so in greater numbers. Preference for altered habitat was unexpected because these habitats had lower resource availability but preference may be explained by the role of mud flat as an influential cue, which would increase the attractiveness of agricultural wetlands. However, behavioral analysis indicates that migrants have adapted to using novel habitats through increased foraging efficiency. Despite their apparent adaptability to changing conditions, migrant shorebirds may still be susceptible to further population decline as a result of changes in phenology brought about by climate change. Results show that timing of peak migration is correlated with the availability of food resources. Given that shorebird migrants already prefer habitat with lower resource availability, any changes to either invertebrate or migration phenology that is not congruent in both magnitude and direction to the other could have severe impacts on migrant populations.

Assessing Local and Landscape Constraints on Habitat Management for Grassland and Upland Birds - Christopher Jorgensen

  • Thesis Defense
  • 11/5/2012

Biodiversity loss is an increasing threat and while habitat restoration is beneficial, management actions do not always demonstrate the desired outcome. Understanding why management actions fail is critical, yet often the focus is directed towards assessing habitat relationships at a single scale, failing to consider the importance of ecological mechanisms that act across scales. During 2010-2012, I conducted point counts for grassland birds across Nebraska and assessed habitat relationships over multiple spatial scales to construct predictive species distribution models. Results indicated that landscape scale habitat variables drastically constrained, or alternatively, facilitated the positive effects of local land management for Ring-necked Pheasants. While identifying habitat relationships at multiple spatial scales is important for conservation, understanding the mechanisms underlying habitat selection is critical for ecological theory. Hierarchical theory suggests that ecological processes function concurrently over multiple spatial scales and not all scales may be appropriate in determining species occurrence. I predicted that the spatial scale in which a species forms habitat decisions would correlate with body size, a predictor of life-history expression, if the scale is a function of how the species interacts with its environment. I tested this hypothesis on 10 obligate grassland bird species in Nebraska, USA. For seven species, I found evidence of a characteristic habitat selection scale, but no relationship to body mass. To quantify local habitat quality, a predictor of species occurrence, I assessed the precision of five methods of measuring plant structure using ground-based imagery and processing techniques. I recorded standing herbaceous cover using digital imagery at two locations in a mixed-grass prairie. I compared the precision of the digital imagery vegetation analysis (DIVA) methods and quantified variability within each technique using the coefficient of variation. Vertical herbaceous cover estimates varied among DIVA techniques but the precision of four of the five techniques was consistently high. Overall, DIVA techniques are sufficient for measuring standing herbaceous cover and can adequately reduce measurement error associated with multiple observers.

Impacts of Recent Climate Change on the Surface Water Balance of the Central United States, 1984-2007 - Bo Dong

  • Thesis Defense
  • 10/4/2012

The climate system and the hydrologic cycle are strongly connected with each other. Understanding the interactions between these two systems is important, since variations in climate can trigger extensive changes in the hydrologic cycle, with significant impacts on agriculture, ecosystems, and society. Observations over the central U.S. in recent decades show numerous changes in climatic variables. This includes decreases in cloud cover and wind speed, increases in air temperature, and seasonal shifts in precipitation rate and rain/snow fraction. To assess the impacts of these variations in climate on the regional water cycle, a terrestrial ecosystem/land surface hydrologic model (Agro-IBIS) is employed in this study, forced by observed climatic inputs for the period 1984-2007. The results generally show an acceleration of the water cycle in the Upper Mississippi, Missouri, Ohio, and Great Lakes basins, but with significant seasonal and spatial complexity. Over the past 24 years, evapotranspiration has increased in most regions and most seasons, particularly during the fall, which is also a time of pronounced solar brightening. Trends in runoff are characterized by distinct spatial and seasonal variations. Since recent warming has led to a greater fraction of winter precipitation falling as rain rather than snow, spring runoff in some snow-dominated regions (such as the northern Great Lakes) has declined significantly since 1984. Other regions, however, such as the northern Missouri basin, show large increases in runoff throughout all seasons, primarily as a result of increased precipitation. Sensitivity experiments show that the water balance is most linearly sensitive to solar radiation and relative humidity, followed by precipitation, air temperature and wind speed. Because of the interdependencies among the climate factors, the hydrological responses of climate change are highly non-linear. Seasonal hydrological responses are notably dependent on regional water and energy availability, and are affected by seasonal conditions of soil moisture and snow cover. Furthermore, precipitation is characterized as the predominant factor that affects the decadal scale hydroclimatic changes in the central U.S.

INTERACTIONS OF ZOOPLANKTON AND PHYTOPLANKTON WITH CYANOBACTERIA - Becky Alexander

  • Thesis Defense
  • 9/12/2012

Cyanobacteria are a major concern in Nebraska reservoirs and are capable of producing toxins that can cause skin irritations, gastrointestinal issues, and affect the nervous system. It is important to determine the mechanisms that can cause cyanobacteria blooms and a lot of work has gone into determining the abiotic factors that can contribute to this. The interaction of zooplankton and other phytoplankton groups with cyanobacteria is also important because there is also a biological aspect in surface waters. Weekly samples were collected from six Nebraska reservoirs and analyzed to determine the interactions of zooplankton and phytoplankton with cyanobacteria using generalized additive modeling and polynomial regression. Significant effects of cyanobacteria were found on Bacillaripohyte. No significant effects were found on Euglenphyte, Chlorophyte, or Dinoflagellates. No significant of cyanobacteria was found with broad groups such as cladocera, copepod, or rotifers. Cyanobacteria had a significant on Bosmina and copepod nauplii, but did not have significant effects on Daphnia, other cladocerans, cyclopoid copepods, and calanoid copepods. Biomanipulation can prove to have positive results in surface waters, but further research is needed to determine its effectiveness in Nebraska reservoirs, this study provides the first steps in helping to establish its possible effectiveness by determining the interactions of those groups with cyanobacteria.

THE RELATIONSHIP BETWEEN DIVERSITY, SEEDING DENSITY, AND ECOLOGICAL FUNCTIONS IN TALLGRASS PRAIRIE RESTORATIONS - Kristine Nemec

  • Dissertation Defense
  • 9/7/2012

In recent decades, agricultural producers and conservation organizations have converted thousands of hectares of cropland to grassland in the Great Plains. Although high diversity seed mixes can cost up to five to ten times as much as low diversity seed mixes, little information is available on the ecological functions that may result from the added diversity. Restorations that maintain critical ecological functions and services may help maintain functional and resilient working landscapes. In this dissertation I assessed the effects of tallgrass prairie plant diversity and seeding density on the provision of ecological functions and services including: 1) resistance to invasive plant species, 2) abundance and diversity of predatory invertebrates, 3) herbivory levels on two perennial forbs, and 4) soil development. In the spring of 2006, twenty-four 55m2-plots were planted to six replicates in each of four treatments: high diversity sites of 97 species typically planted by The Nature Conservancy planted at a lower seeding density, high diversity sites at twice this seeding rate, and low diversity sites using a Natural Resources Conservation Service (NRCS) Conservation Reserve Program mix (CP25; 15species), at low and high seeding densities. This study is among the first to compare the ecological functions provided by grassland seed mixes commonly used by practitioners. Increasing plant community diversity was found to be more important than increasing seeding density for enhancing resistance to invasion by unsown perennial forbs and legumes and in reducing inflorescence production byBromus inermis. There was a significant positive relationship between plant community diversity and the abundance of coccinellid beetles, but the abundance of ants, carabid beetles, and spiders showed no significant response to diversity or seeding density. Seeding density had a positive effect on carabid beetle and spider species richness and Shannon-Weaver diversity. Year was the main significant effect for explaining levels of herbivory damage in Ratibida columnifera and Solidago canadensis and there was a significant negative relationship between diversity and levels of soil nitrate. Overall, results indicate increasing diversity may be more important than increasing seeding density for provision of the ecological functions studied.

Using Landscape Metrics to Characterize Ecoregions - Martha Posada Posada

  • Thesis Defense
  • 8/27/2012

n/a

CHANNEL CATFISH POPULATION DYNAMICS, ABUNDANCE ESTIMATES, AND SHORT-TERM TRENDS IN THE PLATTE RIVER, NEBRASKA - Aaron Blank

  • Thesis Defense
  • 7/24/2012

Fishing for channel catfish Ictalurus punctatus is popular in Nebraska and channel catfish are the most sought after fish species in the Platte River. Anglers on the Platte River are also harvest oriented. Little is known about the effects anglers have on channel catfish population dynamics in the lower Platte River. The goal of this study was to determine if there were effects of angling on channel catfish at two high use fishing areas in the lower Platte River. My first objective was to evaluate differences in relative abundance, size structure, condition, age structure, growth, and mortality between two high use areas (near Fremont and Louisville, NE). I also used a robust design capture-mark-recapture study to estimate density and abundance of channel catfish > 200 mm within a 10-km stretch of the Platte River at each sampling site. The second objective was to assess the 5 year standardized monitoring data for spatial and temporal differences in relative abundance, size structure, condition, age structure, growth, and mortality across two river reaches and three river segments. Channel catfish at Fremont displayed lower size structure, slower growth, and were more abundant compared to channel catfish at Louisville. Population characteristics displayed considerable variation throughout the Platte River in the last five years. However, channel catfish sampled between the Loup River power canal and the Elkhorn River confluence were more abundant, grew slower, and had a lower size structure compared to channel catfish above and below that segment. Key factors influencing differences in channel catfish population characteristics may be due to hydrology (e.g., flow modifications caused by the Loup River power canal, irrigation withdrawals, and precipitation amounts) and the resulting changes to other abiotic factors (e.g., water temperature extremes, ice flow), angler exploitation, predation, habitat characteristics, and tributary inflows.

The Impact of A. Canescens on Water Uptake Patterns of Herbaceous Plants in a Nebraska Sandhills Grassland - Adam Yarina

  • Thesis Defense
  • 7/23/2012

This study investigated the ecophysiological role of Amorpha canescens, a leguminous shrub native to the Nebraska Sandhills. Although A. canescens is an important ecological player in the Sandhills, its impacts on the surrounding plant community are poorly understood. To remedy this, two sites were selected for study at the Gudmundsen Sandhills Laboratory near Whitman, Nebraska--one with A. canescens (G-L) and one without A. canescens (G-NL). Both sites contained five representative herbaceous species: two C3 grasses (Hesperostipa comata and Koeleria macrantha), two C4 grasses (Andropogon hallii and Calamovilfa longifolia), and one forb (Helianthus pauciflorus). Plant canopy cover and aboveground biomass were characterized on both sites in June and August 2010, along with soil composition, organic matter, carbon, and nitrogen content. Seasonal trends in transpiration (E), water use efficiency (WUE), and predawn (ψpre) and midday (ψmid) water potentials were determined for all species in both plots at 2-week intervals from June through September. Precipitation, groundwater, plant root crown, and soil water samples were collected to determine sources of plant water uptake via stable isotope analysis and the IsoSource mixing model. The results indicate that the presence of A. canescens is favorable to C3 grasses when water is plentiful. However, under water limited conditions, the additional demands on shallow soil water coupled with increased rainfall interception from shrub canopy and litter were disadvantageous to C3 grasses. A. canescens also appeared to enhance the amount of water available deeper in the soil profile, resulting in greater overall moisture in the upper 1 m of soil. Water resource partitioning was not observed during the wetter periods in the first half of the study period, with all species predominantly using shallow soil water. However, H. pauciflorus and A. canescens switched to deeper water sources as water became limited, while C3 and C4 grasses senesced or reduced stomatal conductance to limit water loss. The ecological implications of these results are discussed.

INTERACTIONS AMONG EVAPORATION, ICE COVER, AND WATER TEMPERATURE ON LAKE SUPERIOR: DECADAL, INTERANNUAL, AND SEASONAL VARIABILITY - Katie Van Cleave

  • Thesis Defense
  • 7/23/2012

Lake Superior, the largest freshwater lake in the world by surface area, has enormous impacts on the regional weather and climate. The lake also comprises over half of the total volume of water in the Great Lakes system and is an important resource for commercial shipping, water supplies, hydropower, recreation, and aquatic ecosystems. Water temperature and evaporation on Lake Superior have been found to be increasing in recent decades, while ice cover has been decreasing at a very rapid pace. A careful analysis of the long-term trends, however, shows that these changes have not been linear through time. Rather, a step-change occurred in 1997/98 that resulted in a drop in ice duration of nearly 40 days, 3°C increase in summer water temperature, and near doubling of July-August evaporation rates. Linear regression analysis of data on either side of this step change shows trends which are largely insignificant and often opposite in sign. Observation of the step change across multiple datasets suggests important interactions among the three variables. Using time-lagged correlation and composite analysis, these interactions are explored across seasonal and interannual timescales. Fall evaporation rates are found to be significantly correlated with ice cover in the following winter, presumably as a result of strong latent heat flux leading to rapid ice onset and growth. Similarly, ice cover is found to be a strong determinant of summer water temperature.This, in turn, can lead to increases in late-summer evaporation rates. Quantifying these complex interactions is important for assessing the potential impacts of future climate change on large-lake systems. Key to this understanding is the direct measurement of lake-surface processes such as evaporation and sensible heat flux. As such, this study includes an analysis of the first direct observations of nearshore evaporation rates on the Great Lakes, using eddy covariance data collected from a monitoring station on Granite Island (near Marquette, Michigan). The data are analyzed for the period October 2010 to April 2012 to explore the seasonal and interannual variations in latent and sensible heat fluxes over Lake Superior, as well as the primary climatic factors driving this variability.

CHRARCTERIZATION OF THE STREAM-AQUIFER HYDROLOGIC CONNECTION IN THE ELKHORN RIVER BASIN - Zhaowei Wang

  • Thesis Defense
  • 7/20/2012

In this study, the hydrologic relationship between the Elkhorn River and surrounding aquifer at eight study sites were studied. First, the lag effect between groundwater level and stream stage was examined using cross-correlation analysis. Then, the geological model was built based on the well log data to reflect the hydrogeological heterogeneity of the High Plains Aquifer. Last, a groundwater model was built on the basis of the geological model and the stream depletion at Neligh and Hadar site was calculated and analyzed.

The calculated hydraulic gradient showed that the adjacent aquifer recharges the Elkhorn River all year. Reversed gradient was only found at Atkinson site during pumping season. Geoprobe log data and in-situ permeameter tests data were combined to calculate the equivalent hydraulic conductivity(K) and unit-length streambed conductance(C) at eight sites, where the K and C were the greatest at Neligh (0.24 ft/d and 0.811 ft2/d) and lowest at Hadar (0.005 ft/d and 0.009 ft2/d). Accordingly, the cross correlation between stream stage and groundwater level was high at Neligh where the correlation coefficient(Ce) was 0.762 at stream stage lag of 1 day and was low at Hadar where Ce was 0.457 at stream stage lag of 100 days.

This phenomenon suggested that low streambed conductance will not only reduce level of connectedness between stream and adjacent aquifer but also result in longer time for river to respond to the variation of groundwater level in the adjacent aquifer. Lag effect was also found between air temperature and groundwater temperature and the extent of groundwater temperature variation is more pronounced in the Quaternary aquifer than it in the Ogallala aquifer.

A geological model of multimillion grids was built based on well log data of test holes and registered wells using IDW interpolation method. The grids were grouped into eight hydrofacies and their corresponding hydraulic conductivity values were assigned based on empirical value from books and former studies in this area. Then the geological model was upscaled to three aquifer units by coarser grid using an averaging technique (Li, 1999) and bound method (Cardwell, 1945). For each aquifer unit, the hydraulic conductivity of the coarser grid was zoned into hydrogeological property zone of Kx, Ky and Kz based on the number of frequency. In the end, the hydrogeological property zone was imported into the ground water model for each layer.

A groundwater flow model (ULEN) was constructed using MODFLOW to calculate the stream depletion ratio at Neligh and Hadar site. A hypothetical well was created and pumped water at a rate of 100 GPM under three scenarios: the well is located from the river at 1000 ft, 1 mile and 3 miles. The modeling results are consistent with the data analysis which showed that the stream depletion ratio is more pronounced at Neligh than Hadar.

AGRICULTURAL LANDUSE CHANGE IMPACTS ON BIOENERGY PROUDCTION, AVIFAUNA AND WATER USE IN NEBRASKA'S RAINWATER BASIN - Dan Uden

  • Thesis Defense
  • 7/9/2012

Agriculture is an economically important form of landuse in the North American Great Plains. Since 19th Century European settlement, conversion of grasslands to rowcrops has increased food and bioenergy production, but has decreased wildlife habitat. Future agricultural landuse changes may be driven by alternative energy demands and regional climatic changes. Landuse change and its drivers could affect bioenergy production, wildlife populations and natural resources, and considering the potential impacts of impending changes in advance could assist with preparations for an uncertain future.

This study addressed how the conversion of marginally productive agricultural lands in the Rainwater Basin region of south-central Nebraska, U.S.A. to bioenergy switchgrass (Panicum virgatum) might impact ethanol production, grassland bird populations and agricultural groundwater withdrawals. This study also used multi-model inference to develop predictive models explaining annual variation in springtime wetland occurrence and flooded area in the Rainwater Basin.

Results suggest that cellulosic ethanol production from switchgrass and residual maize (Zea mays) stover within existing starch-based ethanol plant service areas is feasible at current feedstock yields, removal rates and bioconversion efficiencies. Throughout the Rainwater Basin, the replacement of marginally productive rowcrop fields with switchgrass could increase ethanol production, conserve groundwater and benefit grassland birds under novel future climatic conditions. However, converting Conservation Reserve Program (CRP) grasslands to switchgrass could be detrimental to grassland bird populations. Predictive wetland inundation models suggest that surrounding agricultural landuse, wetland hydric footprint shape complexity, and autumn and winter precipitation and temperature are strong drivers of springtime wetland occurrence and flooded area in the Rainwater Basin.

Field-Scale Adaption of a Process-Based Index Model for Landscape Vulnerability to Surface and Ground Water Contamination - Atefeh Hosseini

  • Thesis Defense
  • 7/5/2012

Identifying areas vulnerable to off-site agrichemical movement and surface and ground water contamination through conventional data collection is labor-intensive, costly and time-consuming. To promote efficient pesticide use and protect water resources, a process-based index model was previously developed to project landscape vulnerability to pesticide runoff and leaching at a watershed scale. Because mitigation of agrichemical contamination requires implementation of best management practices, the model was adapted to the field scale. To develop the field-scale model, a Digital Elevation Model (DEM) with 5 x 5 m resolution was created for a research field site in Boone County, Missouri based on elevation measured using the Veris Soil EC Mapping System. The model uses input variables and functions associated with hydrologic and pesticide dissipation processes. These variables include the physicochemical properties of pesticide, including adsorption (organic carbon partition coefficient), relative persistence (half-life), and susceptibility to abiotic hydrolysis; along with the saturated hydraulic conductivity of the soil, slope, unfilled pore volume above the restrictive layer (where present), and erodibility. These data were obtained from field measurements, Agricultural Policy/Environmental eXtender (APEX) model output, the Soil Survey Geographic (SSURGO) database, and pesticide property references. Atrazine loss in runoff projected by the model was compared with that measured at the outlet of the Missouri field for years in which corn was planted (odd years) from 1993 to 2001. Because abiotic hydrolysis is critical to the fate of acid-sensitive herbicides such as atrazine, sensitivity analysis was performed to determine a suitable hydrolysis time frame. To accommodate the impact of a restrictive clay layer (claypan) in runoff-prone areas, three modifiers were tested based on the capacity of soil to store water above the claypan. Mathematical functions included in the model were imported into ArcGIS and vulnerable areas within a field were identified by stacking the maps generated in GIS. Results showed that the spatial variability of areas vulnerable to atrazine runoff is primarily controlled by soil pH and adsorption capacity (OM and clay content). Validation of the field-scale model using five years of herbicide transport data demonstrated the capability of the model to estimate atrazine loss through runoff. Atrazine loss projected by the model was highly correlated with measurements at the field outlet, although model estimates exceeded field measurements. It is envisioned that the model can be used to provide practical advisories for pesticide application and targeting of appropriate management practices in vulnerable areas within agricultural fields. The filed-scale model can also help establish a basis for development and implementation of best management practices (BMPs) and regulatory strategies that effectively address water quality issues.

River Otter (Lontra Canadensis) Home Range, Habitat Use, Overnight movement, and Survival in the Platte River of Nebraska - Sam Wilson

  • Thesis Defense
  • 6/28/2012

River otters (Lontra canadensis) are native to Nebraska but were extirpated by the early 1900s. The Nebraska Game and Parks Commission (NGPC) reintroduced river otters during 1986 to 1991 in order to restore the species in the state but little is known regarding the habitat needs and status of this high profile threatened species. In order to provide information for management I conducted research to determine home range, habitat use, overnight movement distance, and annual survival of river otters in the central Platte River of Nebraska. I trapped, implanted telemetry transmitters, and tracked 18 river otters during 2006 to 2009. I obtained 996 telemetry locations and constructed 13 annual home ranges. Male home ranges were larger than female home ranges. Habitat use was determined by comparing used versus available habitats using compositional analysis. Open water was used more than any other habitat type in all three comparisons tested. I recorded 19 overnight movements (465 total telemetry locations) for four river otters during 2007 to 2008. Movements during Jan to Feb when NGPC conducts winter bridge surveys were lower than during the rest of the year. Annual survival was 100% as no river otter mortalities were detected during the study (Oct 2006 to Dec 2009). River otters in the central Platte River select open water over other habitat types, exhibit reduced movements during winter months, and have high annual survival. This information will be used by NGPC to assess the status of river otters in Nebraska and direct management efforts for the species.

Occurrence and Effect of Algal Neurotoxins in Nebraska Freshwater Ecosystems - Maitham Al-Sammak

  • Dissertation Defense
  • 6/15/2012

n/a

The Impact of Place Attachment on Land Succession of Nebraska Agriculturists - Shari Kunert

  • Thesis Defense
  • 6/13/2012

Many Nebraska agriculturists rely on small family farms for their livelihood. The farm is their source of income and may be an important inheritance for their family when they retire or die. Land succession planning is a process to allow landowners to pass farmland on to the next generation without incurring a potentially debilitating tax liability for the heirs. The purpose of this study is to determine the influence of place attachment on land succession planning of Nebraska agriculturists. This comparative research, mixed methods in nature, involves Nebraska agriculturists who have a land succession plan and Nebraska agriculturists who do not have a land succession plan, and are both within 10 years of retirement and beyond retirement.

A Climatological Analysis of the Warm- Season Wind Regimes of the Beaufort Chukchi Seas Coasts - B. J. Baule

  • Thesis Defense
  • 6/13/2012

Climate records for wind speed, wind direction, and temperature are analyzed for the period from 1979-2009 for the Beaufort Chukchi Seas region of the Arctic. Wind records have historically been subject to far fewer analyses than other meteorological variables, such as temperature or precipitation. This is particularly true for data sparse regions. Data were collected for a large area in the Beaufort Chukchi Seas region, which includes portions of Russia, The United States, and Canada. A total of 256 stations were collected from a variety of networks throughout the region and uniformly quality controlled using automated and manual procedures. Eight long-term stations were identified for data completeness and length of record. Climatologies were developed for these eight stations for wind speed, wind direction, and temperature for the period from 1979-2009. Trends in monthly and annual wind speed and temperature were examined. Results from the climatologies and trend tests were then compared to gridded output from the North American Regional Reanalysis (NARR). Using a combination of data sets, a case study focusing on warm-season seas breezes in a smaller study area was performed for the 2009 warm-season. Climatologies show an Arctic climate with clear distinctions between coastal and interior locations for the variables analyzed and strong seasonal characteristics. Strong warming was evident at all locations, particularly in the late warm-season/early cold-season. Negative wind speed trends were observed at several locations, though seasonality was less evident. Biases in NARR were noted for variables analyzed. Trends in NARR temperature compared well with observations in sign and magnitude. Wind speed trends were not well represented in the reanalyzed dataset. Further investigations into physical mechanism behind wind speed trends and differences in reanalysis are required. Sea breezes were found to occur around Deadhorse, Alaska in the summer of 2009. Frequency was highest in June (43% of days) decreasing through the warm season (26% of days). Direction and inland penetration of sea breezes appears to be realted to the strength of the temperature gradient over the region.

Evaluating Vegetation Response to Water Stress using Close-range and Satellite Remote Sensing - Sharmistha Swain

  • Dissertation Defense
  • 5/17/2012

During the last century, almost all parts of the contiguous U.S. had experienced several prolonged drought events with considerable impacts on the agricultural economy and environment. With changing climates, the drought events are expected to be more severe, longer, and widespread in many parts of the world. Understanding vegetation response to water stress using remote sensing technologies will enhance our ability to detect and monitor drought. This dissertation research evaluates the response of vegetation to drought-related water stress at the leaf, canopy, and regional scales using close-range and satellite based reflectance and/or thermal data. At the leaf level, a crop water stress index-based model was developed using high spatial resolution thermal imageries to estimate water content in soybean leaves. The model showed a higher accuracy in leaf water content estimation as compared to water content estimated using the raw leaf temperature. At the canopy level, multi-year close-range reflectance based vegetation indices (VIs) data were correlated with soil moisture measured at four depths of corn and soybean root zone. Results indicated that corn VIs were significantly related to soil moisture at deeper depths and kept the soil moisture memory for a relatively longer period of time compared to those of soybeans. At the regional scale, Terra-MODIS Land Surface Temperature (LST) and NDVI products were used to detect drought-induced stress on cropland and grassland cover types across the state of Nebraska. Results showed that the majority of the land cover sites experienced statistically significant increase in daytime and nighttime LST and statistically significant decrease in NDVI during the drought-year growing season as compared to the non-drought year. The findings of this dissertation research will contribute toward the development of more robust tools for monitoring drought stress on vegetation.

Chlorophyll-based Models for Remote Estimation of Crop Gross Primary Production: From in situ Measurements to Satellite Observations - Yi Peng

  • Dissertation Defense
  • 5/15/2012

Crop gross primary production (GPP) is the rate at which a cropland captures and stores carbon as biomass. The synoptic and accurate quantification of crop GPP is essential for studying carbon budgets in croplands and monitoring crop status. Remote sensing can be used as a powerful and expedient tool for assessing regional and global crop GPP. The objective of this study is to develop a quantitative technique to remotely estimate crop GPP with in situ measurements and satellite observations. A recently developed model, which relates crop GPP to a product of total crop chlorophyll content and photosynthetically active radiation (PAR), was justified and applied for estimating GPP in maize-soybean croplands. The model was tested at close range with vegetation indices retrieved from in situ measured spectral reflectance and ground-observed incoming PAR, and it was able to provide accurate GPP estimates in maize and soybean under different irrigation practices, crop managements, field histories and climatic conditions. The model was also applied to satellite observations to estimate crop GPP, with vegetation indices retrieved from Landsat and MODIS 250 m data and calculated potential PAR values, which is incoming PAR under a condition of minimal atmospheric aerosol loading. The model using vegetation indices and potential PAR can accurately estimate crop GPP based entirely on remotely sensed data.

Exploration of near Infrared-Red Models for the Remote Estimation of Chlorophyll-a Concentration in Optically Complex Turbid Productive Waters: From In Situ Measurements to Aerial Imagery - Daniela Gurlin

  • Dissertation Defense
  • 5/3/2012

Today the water quality of many inland and coastal waters is compromised by cultural eutrophication in consequence of increased human agricultural and industrial activities. This is reflected in an increase in productivity and changes in the phytoplankton species composition with possible harmful algae blooms. The optical complexity of inland and coastal waters makes the application of remote sensing techniques to monitor the productivity of these waters a difficult task. This study presents a technique for the estimation of chlorophyll-a concentrations, a measure of the productivity of waters and one of the standard water quality parameters for the evaluation of the trophic state of inland and coastal waters, for in situ and aircraft data. The developed algorithms make it possible to estimate chlorophyll-a concentrations without the need for analytical measurements and provide important information for the estimation of the productivity in coastal waters for studies of the carbon budget when they are applied to satellite data.

Predictors of Insect Diversity and Abundance in a Fragmented Tallgrass Prairie Ecosystem - Kody Unstad

  • Thesis Defense
  • 4/26/2012

Despite providing many services, the tallgrass prairie and its ecological community is one of the most endangered ecosystems in North America. Remaining habitat exists as remnants in a highly-fragmented landscape. To make informed conservation decisions we need to better understand the effects of this fragmentation. Using the ecologically important insect groups, ants and ground beetles, this study provides baseline data on the biological diversity of southeast Nebraska prairies and investigates what management, landscape, and habitat characteristics affect them. Pitfall trap sampling was conducted in 23 tallgrass remnants scattered throughout the Southeast Prairies Biologically Unique Landscape in 2010 and 2011. Multi-model inference was used for analysis of the data.

Twenty-eight species of ants were collected with the majority being grassland-obligates. With a positive correlation, model selection results indicate that Shannon diversity of grassland ants is best predicted by the average number of grass species per m2 while their abundance is positively associated with the amount of nearby haymeadow.

Most ants belonged to the Opportunist and Cold Climate Specialist functional groups. A comparison with prior studies indicates this functional group composition to be most similar to cool-temperate forests. Though different habitats, their cooler climates likely produce this similar composition.

Nineteen species of ground beetles were collected, with two species comprising nearly 95% of the collection. These two species are incapable of flight, a physiological factor that may contribute to their high abundances by leaving them hidden from predators. As with grassland ants, the strongest predictor of Shannon diversity for ground beetles was the average number of grass species per m2.

Results suggest that ants and ground beetles are non-randomly distributed in relation to landscape, habitat, and management factors. High abundances of grassland-obligate ants are associated with high amounts of haymeadow suggesting these areas may be a priority for ant conservation. Results also suggest that sites with more grass species sustain more diverse communities of ants and ground beetles, information that can be incorporated into relevant conservation decisions.

Swift Fox Survey Assessment and Estimation of Detection Probability in Sioux County, Nebraska - Lucia Corral Hurtado

  • Thesis Defense
  • 4/17/2012

n/a

Greater Prairie-Chicken Nest and Brood Site Selection and Survival in the Eastern Sandhills of Nebraska - Lars Anderson

  • Thesis Defense
  • 4/16/2012

n/a

Crop Imporvement through Biotechnology: Targeting Drought and Photosynthesis - Saadia Bihmidine

  • Dissertation Defense
  • 4/13/2012

The world population is projected to grow from the current 7 to about 9 billion by 2050. One of the major challenges that will face agriculture in the next few decades is sustainable food production under climate uncertainties and dwindling natural resources to meet the increased global needs for food. Plant biotechnology plays a vital role in meeting this global challenge. The goal of this research was to investigate the use of biotechnology to improve plant photosynthesis, water use efficiency and drought resistance, to either increase yield and/or alleviate the impacts of water stress on biomass and yield. In the first essay, the use of two Arabidopsis thaliana promoters RD29A and RD29B in soybean (Glycine max (L.) Merr.), was investigated and results suggest that they may be useful in controlling transgenes targeted to enhance drought resistance in soybean as long as there are no agronomic penalties associated with low-level expression in the absence of stress. In the second essay, the expression of AQPV1, an aquaporin gene from Chlorella virus MT325, and its effect in mitigating drought stress in tobacco (Nicotiana tabacum) was investigated. Results showed that the transformed AQPV1 plants maintained higher photosynthetic rates, less negative water and osmotic potentials, and accumulated greater biomass compared to control plants. In the third essay, the potential use of C4 enzymes from Cyanobacteria to improve C3 photosynthesis was investigated. The cyanobacterial ictB (inorganic carbon transporter B) and FBP/SBPase (fructose-1,6-/sedoheptulose-1,7-biphosphatase) genes were placed under control of constitutive promoters and introduced into soybean chloroplasts via Agrobacterium-mediated transformation. The former gene is involved in HCO3- accumulation and the latter catalyzes the hydrolysis of both fructose-1,6-bisphosphate and sedoheptulose-1,7-bisphosphate in the Calvin cycle. Leaf physiological data collected in both the greenhouse and the field revealed that transgenic soybeans displayed higher leaf photosynthetic rates compared to control plants. In addition, some of the tested transgenic events performed better than control plants when exposed to soil dry-down experiments. Results from these essays contribute to the ongoing research aiming at using plant genetic manipulations to increase crop productivity and alleviate environmental stresses.

Hydrological Information System: An Integrated System for Modeling, Simulation, Analysis, and Distribution of Climate and Hydrology Data - Baburao Kamble

  • Dissertation Defense
  • 4/10/2012

This principal thrust of this research was to develop an integrated Hydrologic Information System (HIS) with advanced data acquisition, modeling, and processing techniques to simulate hydrological processes, in particularly evapotranspiration (ET), at varying spatial scales using easily and freely available remotely sensing data. A second important component was to develop a web-portal to disseminate hydrological data online for the purpose of improved water management decisions in Nebraska. The five main chapters of this dissertation represent the foundation on which the specific findings within this research are grounded.

A suite of procedures, tools and products related to water consumption in Nebraska, the High Plains, and the nation are investigated and developed, including methods for efficient delivery to end-users and facilitation of effective spatial data handling. The methods and accomplishments described are considered to be a "first cut" in establishing a responsive information production and delivery system to support near-real time resources management, in particular the management of water resources over the High Plains. The products, procedures and architectures are described or developed during this dissertation.

Groundwater Pollution Risk Assessment under Scenarios of Climate and Land Use Change in the Northern Great Plains - Ruopu Li

  • Dissertation Defense
  • 2/9/2012

Modeling groundwater vulnerability to pollution is critical for implementing programs to protect groundwater quality. Groundwater vulnerability is strongly dependent on factors such as depth-to-water, recharge and land use conditions that may change in response to future changes in climate and/or socio-economic conditions. For example, global warming may lead to northward shifts in cropping patterns and changes in crop mixes (and use of farm chemicals) in the Northern Great Plains. Meanwhile, growing demands for biofuels are resulting in expanding corn acreage, and may lead to pressures to remove land from the Conservation Reserve Program (CRP) or otherwise open lands that are currently not cropped to cultivation. Such changes may have significant implications for groundwater quality. In this research, a new modeling framework which employs four sub-models linked within a GIS environment is proposed and evaluated. The research focuses on North Dakota. The results of modeling under several different scenarios suggest that over the next 50 years areas having high vulnerability to pollution will expand northward and/or northwestward in eastern North Dakota. GIS-based models that account for future changes in climate and land use can help decision makers identify potential future threats to groundwater quality, and take early steps to protect this critical resource.

Understanding of the Hydrologic Connections Between Wide-channel and Adjacent Aquifers Using Numerical and Field Techniques - Cheng Cheng

  • Dissertation Defense
  • 1/24/2012

Streambed sedimentary structure plays a vital role in controlling the interactions between the surface water and groundwater. Previous researches usually used a lumped parameter, streambed conductance, to analyze stream-aquifer interactions and assumed that a low-permeability clogging layer occurs at the channel surface. However, a number of recent studies noted that hyporheic processes can affect streambed permeability and declogging processes may exist. Accordingly, the assumption of a low-permeability clogging layer at the channel surface can lead to the underestimations of the real-world stream-aquifer interactions. Streambed vertical hydraulic conductivity (Kv) and thickness (M) are two most important parameters of streambed conductance, and thus a detailed characterization of streambed Kv and M is crucial to understand and quantify the exchange between the near-channel and in-channel water.

In this dissertation, the variations of streambed Kv values relative to the depth are investigated for three rivers (the Big Blue River, the Little Blue River, and the Platte River) in Nebraska. The Kv values in the top 2-m of the streambed sediments are generally larger than 1 m/d. In addition, streambed Kv values have a decreasing below the channel surface, which may be a result of hyporheic process and indicate that stream-aquifer interactions are more intense near the channel surface. Consequently, this study confirms the absence of a low-permeability clogging layer at the channel surface. Furthermore, the estimated values of M may vary largely in space. From these results, the constant head boundary is proposed to be an alternative solution in the simulation of stream-aquifer interactions. This approach is applied in a regional groundwater flow model to evaluate the impact of groundwater irrigation on the streamflow in the lower reach of the Platte River. Additionally, the model provides an accurate estimation of the streambed leakance of the Platte River using numerical and field techniques, which is beneficial in assessing stream-aquifer interactions when an analytical solution is employed. Furthermore, the statistical distribution of streambed Kv values along a 300-km segment of the Platte River is also examined. We found they are normally distributed at nearly each of the 18 test sites in the Platte River.

An evaluation of stocking and habitat influences on channel catfish populations in lentic ecosystems of the Great Plains - Lindsey Chizinski (Richters)

  • Thesis Defense
  • 1/18/2012

Abstract: Channel catfish are highly sought after by Nebraska anglers, and the Nebraska Game and Parks Commission invests considerable resources in statewide stocking programs to establish and maintain the species in Nebraska’s public waters. Assessments of stocking programs are lacking, in large part because channel catfish are ineffectively sampled with current methods. The objective of this study was to utilize a recently developed sampling method, tandem-set hoop nets, to collect channel catfish in sufficient quantities to describe the effects of stocking and habitat variability on populations in lentic ecosystems. Three lentic ecosystems common to the Great Plains were considered: sand pits, flood control reservoirs, and irrigation/power generation reservoirs. The influence of stocking on abundance and condition of channel catfish varied with ecosystem type. In sand pits, stocking negatively influenced fish condition, and only frequent stocking positively influenced abundance. In flood control reservoirs, stocking did not influence fish condition, but was associated with greater abundance. Stocking did not influence fish condition or abundance in irrigation/power generation reservoirs. Additionally, there was evidence that mortality and growth rates varied with ecosystem type. In general, populations from irrigation/power generation reservoirs were predicted to experience slower growth and lower mortality, where as sand pit populations were predicted to experience the fastest growth and highest mortality. This knowledge can inform decisions regarding future stocking protocol for channel catfish and provide fisheries biologists with useful tools for population assessments.

Atrazine Runoff in the Blue River Basin: Geomorphology, Rainfall, and Agronomic Practices - Kundan Dhakal

  • Thesis Defense
  • 12/1/2011

Atrazine concentrations in the Big Blue River Basin in Nebraska and Kansas periodically exceed the EPA Total Maximum Daily Load (TMDL) of 3 mg L-1. The present study is focused on watershed variables influencing surface runoff of atrazine. The assessment includes the impact of corn and sorghum progress (indicating atrazine application), rainfall, antecedent soil water content, and soil restrictive layer on stream-measured weekly atrazine load in independent subwatersheds for 1997 - 2004. Maximum atrazine loading occurred after most of the corn had been planted but during sorghum planting from mid-May to early June, immediately following multiple rainfall events that saturated the soil profile and caused runoff from fields. Analysis of covariance was conducted from day 110 when about 10% of the corn was planted to day 170 when 90% of the sorghum was planted. Results from independent subwatersheds imply that atrazine load weighted by area is related to cumulative weekly rainfall across all years. Statistical analysis showed rainfall was the most significant factor associated with atrazine loading, but soil moisture, corn and sorghum planting progress, and the presence of a soil restrictive layer were also important. Results provide decision support to farmers, agencies, extension workers, and scientists for targeting of best management practices.

Analyzing Ecohydrology of Subirrigated Meadow, Dry Valley and Upland Dune Ecosystems using Remote Sensing and In-Situ Estimations in the Semiarid Sand Hills Region of Nebraska, USA - Nathan Healey

  • Dissertation Defense
  • 11/30/2011

Nebraska,s dependence upon the High Plains (Ogallala) Aquifer for agricultural production is vital to the state,s economy, ecology and hydrology. The Sand Hills region (58,000 km2) of Nebraska is a unique system of lakes, (~5%) wetlands, (~10%) subirrigated meadows, (~20%) dry valleys and (~65%) upland sand dune ecosystems. Understanding how each of these land cover types reacts to climate conditions of different water limitations is vital to regional water resource management. This research explores the ecohydrological behavior of different land cover types at the Gudmundsen Sand Hills Research Laboratory (GSRL) near Whitman, Nebraska in the heart of the Sand Hills region of Nebraska by using remote sensing and in-situ estimations of energy partitioning. By employing satellite technology and micrometeorological instrumentation this research establishes a better understanding how energy partitioning, and resulting evapotranspiration (ET), differs between different vegetative communities. We present findings of diurnal and seasonal estimates of energy partitioning as well as daily estimations of ET from both satellite image processing and in-situ observations by Bowen ratio energy balance systems (BREBS). This research also employed different techniques to estimate energy partitioning via remote sensing by adjusting radiation, wind speed, and stability parameters to better represent areas with high topographic relief. The last focal point of this research was to analyze how energy partitioning and ET varied both spatially and temporally under different climate conditions between 2004 (normal year), 2006 (dry year), and 2009 (wet year).

Ecophysiological Responses of Herbaceous Plants to the Presence or Absence of Leadplant (Amorpha Canescens) in a Nebraska Sandhills Grassland - Jessica Milby

  • Thesis Defense
  • 11/28/2011

Deeply-rooted shrubs are common component of grasslands. This study investigated the ecophysiological role of leadplant (Amorpha canescens), a common leguminous shrub, in Sandhills grassland, and response of herbaceous plants to the presence or absence of leadplant. Two sites were selected for the study at the Gudmundsen Sandhills Laboratory near Whitman, Nebraska—one with leadplant (G-L) and one without (G-NL) leadplant. Species diversity, plant canopy cover and aboveground biomass were characterized on both sites in June and August 2010. Seasonal trends in net photosynthesis (A), stomatal conductance (gs), transpiration €, water use efficiency (WUE), and predawn (ψpre) and midday (ψmid) water potentials of leadplant and five representative herbaceous species were determined twice a month, and carbon isotope ratio (ä15C) and specific leaf area (SLA) were determined once a month between June and September. The herbaceous species included two C3 grasses [needleandthread (Hesperostipa comata) and prairie junegrass (Koeleria macrantha)], two C4 grasses [sand bluestem (Andropogon hallii) and prairie sandreed (Calomovilfa longifolia)], and one forb [stiff sunflower (Helianthus pauciflorus)]. Differences in rates of A, gs, and WUE were species dependent and were not impacted by the presence of leadplant. Net photosynthesis exhibited seasonal variability, increasing early in the growing season and peaking by midsummer. The C3 stiff sunflower had the highest rates of A, E, and gs; and the C4 grasses had the greatest WUE. Site significant impact (G-L vs. G-NL) was only observed in E, which was likely related to higher soil water content in the G-L site. ψpre and ψmid differed significantly among sampling dates and species, but not between sites. The C3 grasses exhibited the lowest (most negative) ψpre and ψmid. Leadplant improved soil nitrogen content on the G-L site, resulting in higher leaf N content, and lower photosynthetic nitrogen use efficiency (PNUE) in plants on the G-L compared to the G-NL site. Leadplant presence had positive impacts on soil and associated plants’ leaf nitrogen content and soil water content. Ecological significance of the results is discussed.

ABIOTIC STRESS RESPONSES IN PHOTOSYNTHETIC ORGANISMS - Joseph Msanne

  • Dissertation Defense
  • 11/22/2011

Cellular and molecular aspects of abiotic stress responses in Arabidopsis thalianasubjected to cold, drought, and high salinity; and in two photosynthetic green alga Chlamydomonas reinhardtii and Coccomyxa sp. C-169 subjected to nitrogen deprivation were investigated. Cold, drought, and high salinity can negatively affect plant growth and crop production. The first research aimed at determining the physiological functions of the stress-responsive Arabidopsis thaliana RD29A and RD29B genes. Cold, drought, and salt induced both genes; the promoter of RD29Awas found to be more responsive to drought and cold stresses, whereas the promoter of RD29Bwas highly responsive to salt stress. Therefore, RD29A and RD29B gene sequences have the potential to confer abiotic stress resistance in crop species grown in arid and semi-arid regions. RD29A and RD29B proteins were also found to unlikely serve directly as protective molecules. The second study aimed at investigating the impacts nitrogen deprivation in Chlamydomonas reinhardtii and Coccomyxa sp. C-169, results showed that these microalgae altered their lipid metabolism by synthesizing and accumulating the neutral lipid triacylglycerol (TAG). Since microalgae have emerged as suitable feedstocks for renewable biofuel production, the purpose of this analysis was to understand the genetic and biochemical mechanisms associated with the induction of TAG synthesis in Chlamydomonas and Coccomyxa subjected to nitrogen deprivation under photoautotrophic conditions. In addition to TAG accumulation, nitrogen depletion triggered an early synthesis of starch and up-regulation of several genes in Chlamydomonas, including some diacylglycerol:acyl-CoA acyltransferases, catalyzing the acylation of diacylglycerol to TAG. Protein degradation in nitrogen-deprived cells might provide carbon skeletons for TAG biosynthesis. In a related study, the effects of the autophagy-inducer rapamycin and the autophagy-inhibitor 3-methyladenine (3-MA) on the accumulation of TAG in Chlamydomonas cells subjected to nitrogen deprivation were investigated. 3-MA induced TAG accumulation in cells growing in both nitrogen-deprived and control media. The increase in TAG content in cells subjected to nitrogen deprivation might not be a direct response to an autophagic activity induced by nutrient depletion.

Climatic controls on the summertime energy balance of a thermokarst lake in northern Alaska: Short-term, seasonal, and interannual variability - Brittany Potter

  • Thesis Defense
  • 11/21/2011

Shallow, thermokarst lakes that develop atop permafrost are a prominent landscape feature on the Arctic Coastal Plain (ACP) of northern Alaska. The ACP is vulnerable to ongoing climate change and landscape modification, as thousands of thaw lakes and ponds are impacted by changes in temperature, precipitation, thawing permafrost, and human activity. Although summer in the Arctic is short, incoming solar radiation and lake evaporation are relatively high, and both factors play a significant role in the landscape water balance. Furthermore, lake evaporation is anticipated to increase as the ice-free season lengthens and water temperatures become warmer. To improve our understanding of these processes, we performed a multi-year energy balance analysis of a shallow, thermokarst lake near Barrow, Alaska. Timeseries of net radiation, Bowen ratio, and rates of heat storage in the water and sediments were used to calculate sensible and latent heat fluxes during the 2008-2010 ice-free periods. Results of the energy balance analysis show rapid lake warming immediately following ice-off (due to high insolation), followed by similar increases in sensible and latent heat flux. Lake evaporation averaged around 1.3 mm/day during the ice-free period, which is nearly twice the mean summertime precipitation rate of 0.7 mm/day for Barrow, Alaska. Daily evaporation rates ranged from zero to greater than 4 mm/day, while short-term and seasonal patterns varied significantly from one year to the next. Much of this variability was associated with changes in cloud cover, water temperature, relative humidity, and wind speed.

Habitat Use and Abundance Patterns of Sandhill Cranes in the Central Platte River Valley, Nebraska, 2003-2010. - Todd Buckley

  • Thesis Defense
  • 11/2/2011

The Central Platte River Valley (CPRV) in Nebraska is an important spring stopover area for the midcontinent population of sandhill cranes (Grus canadensis). Alterations to crop rotation and loss of native habitat in the CPRV pose a risk to the future population. Personnel made observations of agricultural fields along designated routes in the CPRV from 2003-2010 to record the presence of cranes and estimate abundance. I developed and evaluated models to predict habitat use and flock sizes of cranes. My results suggest diverse crop rotations in large fields far from development but near roosting habitat are the most beneficial stopover habitat conditions for cranes in the CPRV. However, seasonal variation in the distance travelled to fields suggests roosting habitat might be limiting the distribution of cranes. Understanding the use of the Platte River by cranes is critical for future management of roosting habitat. Personnel made observations of the Platte River during aerial surveys from 2004-2010 to determine the presence of cranes and estimate roost sizes. I developed and evaluated models to predict roosting habitat use and roost sizes. Segments of the Platte River not adjacent to disturbance, wider than 150 meters, and free of tall woody vegetation received the highest use and contained the largest roosts. The results of my entire study suggest management in the CPRV for cranes should be focused west of Kearney, Nebraska, due to the potential for roosting habitat expansion and the characteristics of surrounding agricultural fields.

Impact of copper mine tailings (stamp sand) on survival and development of aquatic organisms near Gay, Michigan. - Danielle Haak

  • Thesis Defense
  • 8/1/2011

n/a

Using slow-release permanganate to remove TCE from a low permeable aquifer at a former landfill - Mark Christenson

  • Thesis Defense
  • 7/18/2011

Past disposal of industrial solvents into unregulated landfills is a significant source of groundwater contamination. In 2009, we began investigating a former unregulated landfill with known trichloroethene (TCE) contamination. Our objective was to pinpoint the location of the plume and treat the TCE by in situ chemical oxidation (ISCO). We accomplished this by using electrical resistivity imaging (ERI) to survey the landfill and map the subsurface lithology. We then used the ERI maps to guide groundwater sampling via direct push. A TCE plume (100-600 µg L-1) was identified in a low permeable silty-clay aquifer (Kh = 0.5 m d-1) that was within 6 m of ground surface and underlain by an even lower permeable zone (Kh = 0.04 m d-1). Because injecting a liquid oxidant into the low permeable aquifer would have been difficult, we manufactured slow-release potassium permanganate candles (SRPCs) to treat the TCE. SRPCs were prepared by heating and mixing KMnO4 and paraffin wax at a 4.6 to 1 ratio (w/w), and then pouring the heated mixture into circular cardboard molds (91.4 cm long) that were either 5.1 cm (2 in) or 7.6 cm (3 in) in diameter. For comparison, we inserted equal masses of SRPCs (7.6-cm vs 5.1-cm diam) into a low permeable aquifer (4.6 m vertical thickness) in staggered rows that intersected the TCE plume. The 5.1-cm diam candles were inserted directly into the formation using direct push hollow rods at 21 locations. The 7.6-cm SRPCs were encased in slotted containers and placed in 10 permanent wells. Pneumatic recirculators that emitted small air bubbles were placed at the bottom of the 7.6-cm SRPCs in the second year to facilitate permanganate distribution. Results obtained prior to inserting recirculators showed a 64 to 82% reduction of TCE in the 7.6-cm candle treatment zone after 342 d and between 64 to 100% decrease in associated ethene degradates. These results support using slow-release permanganate candles as a means of treating chlorinated solvents in low permeable aquifers.

Breeding fidelity and landscapes effects on distribution of mallards and duck broods in the Nebraska Sandhills - Zach Cunningham

  • Thesis Defense
  • 7/15/2011

n/a

Avian Influenza Surveillance in Wild Migratory Birds in the United States, 2007-2009, and Effects of September Hunting Seasons on Survival, Harvest, and Recovery Rates of Canada Geese Banded in Southeast Nebraska - Scott Groepper

  • Thesis Defense
  • 7/12/2011

Highly-pathogenic avian influenza virus (HPAIV H5N1) poses risks to wild birds, poultry, and humans. Personnel with the United States Department of Agriculture-Animal Plant Health Inspection Service-Wildlife Services, state, and tribal wildlife agencies collected 168,940 samples from migratory birds from 2007-2009 to test for presence of HPAIV H5N1. No HPAIV was found, but other subtypes were discovered, including H5 and H7. I estimated prevalence of avian influenza virus by flyway and found prevalence was lowest each year in the Atlantic Flyway (6.7%-8.3%), highest in the Pacific Flyway in 2007 (13.3%) and 2008 (13.4%), and highest in the Mississippi Flyway in 2009 (15.9%). I plotted prevalence monthly and found July-October was optimal time for sampling due to highest prevalence in all flyways. Dabbling ducks had significantly higher prevalence of AIV ( = 14.1%, range = 9.3%-19.4%) than other functional groups across all flyways and study years. My results suggest future surveillance should focus on species from the dabbling duck functional group.

Restoration efforts in Nebraska have contributed to increased populations of resident Canada geese (Branta canadensis) that now are considered a nuisance. In 2004, an early September hunting season was initiated to reduce populations. I analyzed band returns from geese banded in Nebraska to determine if early September hunting seasons affected survival, harvest, and recovery rates. The top model in my survival analysis revealed early September hunting seasons did not reduce survival of geese (S = 0.696). In addition, models indicated survival was not different between geese inside and outside the early hunting zone (southeast vs. northeast, S = 0.711) and survival did not differ by sex (S = 0.708). Survival differed between the metropolitan areas of Omaha and Lincoln, Nebraska (S = 0.742 and 0.678, respectively). A combination of urbanization and non-migratory behavior may be leading to higher survival of geese in Nebraska.

Late Holocene History of Dune Activity Along the Elkhorn River in Northeastern Nebraska - Becky Young

  • Thesis Defense
  • 7/7/2011

The Nebraska Sand Hills have been an important study area for dune activation and the nature of prehistoric drought events in the Great Plains. However, little has been done to understand the impact of these droughts to smaller dune fields along the eastern margin of the Great Plains. This study focuses on the Stanton dune field which is found about 145 km east of the Sand Hills along the southern edge of the Elkhorn River valley in northeastern Nebraska. With a wetter and slightly cooler climate regime than that of the Nebraska Sand Hills and most other central Great Plains dunes, the Stanton dunes could provide valuable insight into the extent of large-scale dune activation and the nature of regional drought events. Twenty-four optically stimulated luminescence (OSL) ages from the Stanton dunes reveal several activation periods that cluster into several distinct groups: less than 120 years ago (n=2), around 410-630 years ago (n = 7), around 1000 years ago (n = 2), and around 3,800 to 5,800 years ago (n = 6). The two younger clusters do not correspond to major dune activation events in the Nebraska Sand Hills, while both of the older periods chronologically overlap with the activation of dunes in the Nebraska Sand Hills and other major central Great Plains dune fields. Optical ages in the Stanton dune field suggest that megadroughts reach far beyond the eastern edge of the Nebraska Sand Hills. Geochemical evidence indicates that the Stanton dunes and the underlying alluvium are similar to the sand found in the Nebraska Sand Hills. The two older dune formation events from the Stanton dunes may be related to drought-induced changes in sediment supply in the Elkhorn River which drains a portion of the Nebraska Sand Hills. Thus, the activation events of the Stanton dunes may have been driven by a combination of drought and changes in sediment supply.

Spatial Accuracy of Climate Networks in Nebraska - Andrea Coop

  • Thesis Defense
  • 7/6/2011

Climate data has become increasingly scrutinized for its accuracy because of the need for reliable predictions about climate change. The U.S. has taken great strides to keep up with the demand for accurate climate data. Over the last thirty years, vast improvements to instrumentation, data collection, and station siting have created more accurate data records. This study is to explore the accuracy of existing networks.

This study analyzes three climate networks used in Nebraska: the U.S. Historical Climatology Network (HCN), the Automated Weather Data Network (AWDN), and the newest network, the U.S. Climate Reference Network (CRN). Each of these networks has its own instrumentation, collection methods and station sites. Maximum and minimum surface temperature from the three networks and the spatial structure of temperature variations at the surface are compared. Two different timeframes, 2005-2009 and 1985-2005, were used to include the newest network, CRN, in the analysis. Daily data was collected from each of these networks within the specified timeframe. Root mean square error (RMSE) between each candidate station and the surrounding stations within 500 kilometers were calculated and evaluated to determine spatial accuracy of the network. This study found that in the 5 year analysis, CRN versus AWDN, the two networks were not significantly different enough to denote the network with high spatial accuracy. For the 21 year analysis, HCN versus AWDN, AWDN stations showed higher spatial accuracy (smaller error) than HCN stations for the variable of maximum temperature. The error for the two networks were not significantly different enough to decipher the network with the higher spatial accuracy.

Discontinuities: Predicting the Architecture of Invasions and Extinctions - Aaron Lotz

  • Dissertation Defense
  • 7/1/2011

One of the major unresolved problems, at the forefront of worldwide environmental concerns, is the increase in non-indigenous species (NIS) and endangered species. Invasions and extinctions fundamentally change community structure, which potentially affects ecosystem processes. This potential loss of ecological processes inherently affects landscape structure and dynamics, including predator-prey interactions, dispersal, foraging behavior and functional group composition.

I explored multiple tenets of the textural discontinuity hypothesis. This hypothesis states that hierarchical landscape structures with scale-specific pattern entrain attributes of animals inhabiting the landscape. Landscapes form hierarchies that are structured by vegetative, geomorphological and contagious disturbance processes. The spatial and temporal patterns inherent in landscapes reflect numerous processes, interacting on distinct scales, which shape the assembly of animal communities. Analysis of body mass patterns and functional group distributions has been suggested as methods to provide insight about these underlying hierarchical processes. Scientists have posited that species at the edges of body mass aggregations may be exposed to highly variable resources. Literature indicates NIS and endangered bird and mammal species occur at the edges of body mass aggregations more frequently than expected. This work focuses on the distribution of biological diversity in space and time and socio-ecological factors that are contributing to the worldwide increase in NIS and endangered species.

I analyzed invasions and extinctions of birds and mammals across five Mediterranean-climate ecosystems and in 100 countries using Bayesian CART analysis and an information-theoretic approach. All body mass distribution data analyzed were discontinuous. This work provided further support for Holling's textural discontinuity hypothesis. Alpha and beta diversity of function decreased in most datasets when NIS were introduced into the community. After the introduction of NIS, I observed a decrease in cross-scale redundancy of functional groups in mammals and when both taxonomic groups were combined. In Eocene Epoch mammal data, speciation events were not detected near body mass aggregation edges. However, this was most likely due to the low power of the statistical tests, high species turnover, and small sample size. Only 64% of the biomes in mammals had ecoregions with similar structure and only 50% of the biomes in birds had ecoregions with similar structure, which may be a result of coarse landscape classification schemes. GDP per capita was positively correlated with the proportion of NIS bird and mammal species within a country. Resilience of a country was correlated to life expectancy. As life expectancy increased, resilience of a country decreased. Results may help us make proper management decisions in monitoring particular non-indigenous species and focus conservation efforts on those native species.

Quantifying Evapotranspiration and Water Table Interactions in Regions of Shallow Groundwater: Sensitivity to Soil Properties, Vegetation, and Climate Variability - Evren Soylu

  • Dissertation Defense
  • 5/27/2011

A growing world population requires increased agricultural production, which relies heavily on irrigation. Up to 90% of fresh water is used for producing food, and sustainable management of water resources requires understanding various components of the hydrologic cycle, including the impacts of human activities and climate on evapotranspiration (ET) and groundwater recharge. Many watersheds around the globe are suffering from declines in streamflow, including the Republican River basin in the central Great Plains. Decreased streamflow can be attributed to human activities – such as land cover change and groundwater consumption – as well as climate variability. In this study, we investigated the interactions between groundwater and ET in shallow water table environments of the central Great Plains region. ET is a major component of the water cycle, plays an important role in the land surface energy and water balance, and interacts strongly with groundwater in riparian zones. We examined the modeled sensitivity of ET to soil parameters and changes in groundwater depth (for a specific field site in the Republican River basin) by means of a hierarchy of land surface models with varying degrees of complexity. The impacts of interannual climate variability and land cover on ET were also investigated for the central Great Plains using a land surface hydrologic / ecosystem model known as Agro-IBIS (the "Integrated Biosphere Simulator"). Finally, a new and improved field method was developed to estimate ET from diurnal fluctuations in shallow groundwater. This technique is similar to the White method, but it uses a multi-day, moving Fourier window to provide more accurate estimates of ET, and it also includes a new formulation for specific yield that facilitates application of the methodology to variably saturated environments (e.g., wetlands with standing water).

Natural Selection and Age-related Variation in Morphology of a Colonial Bird - Mary Bomberger Brown

  • Dissertation Defense
  • 4/18/2011

In May 1996, inclement weather led to the deaths of thousands of Cliff Swallows (Petrochelidon pyrrhonota) in Nebraska. Survivors had larger skeletons, shorter wings and tails, and less wing asymmetry than non-survivors. This population was followed for 10 years to study 1) whether natural selection events result in permanent microevolutionary changes, 2) if variation in climate affects the development of morphological traits, and 3) if morphological traits vary systematically with age.

Patterns in morphology exhibited by swallows following the selection event were studied by measuring yearling birds. Wing and middle tail lengths decreased, beak length and width increased, tarsus length was unchanged, and the amount of wing asymmetry increased. The cumulative directional change in wing, tail, and beak length was greater after the selection event than during the event. This variation was not explained by phenotypic plasticity resulting from better environmental conditions, because conditions were not significantly different before and after the event. There was no evidence opposing selection restored skeletal size or wing or tail length to that before the selection event. This continued change in morphology may represent the population shifting to a different fitness peak in the adaptive landscape.

The way variation in climatic conditions (and food resources) affects the morphological development of juvenile swallows was studied. In cooler years birds allocated less growth to wings and tails than they did in warmer years, while maintaining normal levels of skeletal growth and body mass. Changes in juvenile feather growth in response to rearing conditions persisted into the first breeding season.

The extent morphological traits vary with age across a bird's lifetime was examined. Juveniles had shorter wings and tails, lower body mass, smaller skeletal size and lower levels of fluctuating asymmetry than adults. Among adult age classes, wing and tail length increased with age and wing and tail fluctuating asymmetry decreased with age. There was no evidence for degenerative senescence in swallows, as the decline in fluctuating asymmetry suggests the oldest birds maintain high levels of phenotypic performance. This age-related variation in morphology suggests that age should be considered in future analyses of morphological variation in passerines.

Propagating and Non-propagating Interseasonal Oscillations in the Tropical Atmosphere: Their Vertical and Horizontal Structures and Developing Mechanisms - Zhaoning Liang

  • Dissertation Defense
  • 11/30/2010

A fixed beamformer is proposed and designed to identify source regions of Intra-Seasonal Oscillations (ISO) in the tropical atmosphere. After tested by simulations of single and complex sources of waves, the fixed beamformer is applied to the ECMWF interpolated data grids to detect and identify source regions of the ISO in the tropical Indian and Pacific Ocean region. Results show that the fixed beamforming technique can uniquely identify the source region of the ISO, and the source regions of all major ISO in the tropical Indian and western equatorial Pacific region during the 29 yr from 1974 to 2002 have been identified.

Examinations of ISO development in the source regions indicate that besides the eastward propagating ISO, there were non-propagating ISO during this 29-year period. To understand why some ISO propagate while others are stationary, statistical analyses are used to examine the vertical and horizontal structures of these two types of ISO. Results show very different structures during the development and evolution of these two different types of ISO. For the propagating ISO, both moisture and temperature processes/disturbances are very important for the development of the ISO. This type of ISO is developed in a relatively warm and wet large-scale environment, and wind enhanced surface evaporation is a major mechanism. For the non-propagating ISO, temperature process is not as important as the moisture process in the development of ISO. Temperature anomalies remained weak before the onset of major convection in the ISO and reached peak intensity afterward peak convection. Both temperature and moisture anomalies developed but confined within the source region. The non-propagating ISO develop in a relatively cool and dry environment. Although weak low-level easterly anomalies and surface evaporation existed before the onset of major convection in these ISO, radiation-convection interaction mechanism seems playing an important role in triggering the non-propagating ISO. A key support for this notion is that relatively cold temperature anomalies persisted in the middle troposphere during the development of the ISO. This radiative cooling destabilized the troposphere profile and favored convection development.

Challenges for the Implementation of Adaptive Management and two Quantitative Applications - Jamie McFadden

  • Thesis Defense
  • 11/8/2010

Adaptive management is becoming an increasingly popular management-decision tool within the scientific community. The application of adaptive management is appropriate for complex natural-resources management problems high in uncertainty. Two primary schools of thought have developed that may yield varying levels of success as they primarily differ in stakeholder involvement and model complexity. We evaluated peer-reviewed literature that incorporated adaptive management to identify components of successful adaptive management plans and to make comparisons between the two schools of thought. Identifying the elements of successful adaptive management is advantageous to natural-resources managers considering adaptive management as a decision tool, such as those managing the Platte River, Nebraska. The Platte River is a complex ecosystem where resource management decisions affect endangered and threatened species such as the Interior Least Tern (Sternula antillarum athalassos) and Piping Plover (Charadius melodus). Because high uncertainty is associated with the responses of these species to habitat restoration and other resource uses and management efforts differ between the lower Platte River (LPR) and the central Platte River (CPR), we developed quantitative applications for each section. For terns and plovers on the LPR, we developed a population model that estimates population characteristics for on-channel and off-channel breeding and nesting habitat. The population model is a valuable tool in measuring and managing adaptively the annual status of the two avian species on the LPR. The ability of this quantitative model to adapt to new information makes it ideal for projecting management implications within an adaptive management context. As the CPR is further along in the adaptive management process, we developed a multi-model analysis based on simulated data to simplify hypotheses and prioritizing research and management needs. By utilizing statistical models for evaluating management consequences, iterative decision-making will for continuous updating as more monitoring data becomes available, influencing future management decisions. The process of evaluating effects of ecological features is helpful in setting and prioritizing objectives and implementing actions for adaptively managing complex ecosystems.

Detection and Measurement of Water Stress in Vegetation Using Visible Spectrum Reflectance - Art Zygielbaum

  • Dissertation Defense
  • 12/2/2009

At any scale, from a single microbe to the planet that nurtures us, water defines our place in the universe. It provides the hydraulic forces needed to give plants structure, and the medium enabling photosynthesis, the basis for most life on earth, to occur. Knowledge about the water status of plants is vital to understanding the state or condition of vegetation, which is important to scientists in disciplines as diverse as agriculture, geography, and climatology. Non-destructive and remote sensing of plant water status allows the gathering of such information across wide geographic extents and over long periods of time. During this seminar, the results of extensive greenhouse research on corn and soy plants undergoing water deficit will be presented. The effort resulted in the identification of a previously unknown systematic increase in visible light reflectance as plants become increasingly water stressed. The effect is more pronounced in corn than in soy. Because water molecules do not absorb light in the visible spectral range, this finding offers new insights into the physical and chemical processes which protect plants from damage due to water stress. The finding also suggests a potential for using only visible light to detect and measure plant water status non-destructively, and perhaps even by means of sensors on remote platforms.

The Textural Discontinuity Hypothesis and its relation to nomadism, migration, decline and competition - Aaron Alai

  • Thesis Defense
  • 11/30/2009

The causes of nomadism, migration, and decline in vertebrates are debated issues in the ecological sciences. Literature suggests nomadism may arise in species that specialize in granivory, nectivory, or the utilization of rodent outbreaks. Literature suggests species become migratory because they exploit certain scarce or variable food types. Species decline is hypothesized to be the result of many different factors as well; large species, island species and specialists may be more prone to decline.

A fresh perspective regarding the causes for species nomadism, migration, and decline is being investigated with the Textural Discontinuity Hypothesis. The Textural Discontinuity Hypothesis stems from complex systems analysis and posits that body mass distributions form clusters within ecological systems, and that those body mass clusters reflect discontinuous distributions of resources. Additionally scientists have posited that species at the edges of body mass clusters may be exposed to highly variable resources. Nomadic and declining bird species populations occur at the edges of body mass clusters more frequently than expected. Migratory bird species also may be located at the edges of body mass clusters more frequently than expected. The morphological spacing of species within clusters may yield clues regarding species interactions. The distribution of species within a body mass cluster would have low variance if species within a cluster interact with each other strongly – morphological overdispersion has been documented in many animal communities and reflects strong competitive interactions among species.

I analyzed nomadism, migration, and decline in South African birds using an information-theoretic approach. I assembled a series of plausible models based upon suggested or theoretically predictive characteristics. Additionally, I used a series of Monte Carlo simulations to investigate the distribution of species within clusters, in terms of body mass.

Results suggest that a combination of species characteristics, including the distance to the edge of a body mass cluster, explain the complex phenomena of nomadism, migration and decline. Generally there was no single model supported, and often many models were in the confidence set, providing only weak inference. Within body mass clusters, there is more variance among species than null expectations, thus with my dataset morphological overdispersion is not present within body mass clusters. Nomadism, migration, and decline are complex phenomena which incorporate different species characteristics, perhaps explaining why such debate still exists over the causes of such phenomena

The Effect of Regulation on Household Solid Waste Management in Lincoln and Augsburg: A Comparative Study - Amir Vafa

  • Thesis Defense
  • 11/24/2009

Private household recycling is a significant aspect of consumerism in economically developed countries and the inevitable question of household waste management has gained more importance among municipalities in recent years. The present study examines the effect of regulation on household solid waste management. Within a comparative, qualitative framework, the study explores and evaluates the pro-regulatory effects in Germany and the anti-regulatory policies in the United States by means of comparing two similar communities, Lincoln, Nebraska and Augsburg, Germany. By examining the present legislations, official documents, legal and operational procedures, and other relevant artifacts, laws and regulations the degree of their success are analyzed. The second major element of the study is consumerism, as a phenomenon inherent to industrialized societies. After examining the relationship between regulations and consumption, the results show that a pro-regulatory policy, in the case of Germany, is more sustainable. The results of this study may be valuable for future research, municipal policy makers, recycling program managers, and other interested stakeholders.

Nest and brood survival and habitat selection of ring-necked pheasants and greater prairie-chickens in Nebraska - Ty Matthews

  • Dissertation Defense
  • 11/13/2009

n/a

Satellite-based Esitmation of Chlorophyll-a Concentration in Turbid Productive Waters - Wesley Moses

  • Dissertation Defense
  • 10/8/2009

Inland, coastal, and estuarine waters, which are often turbid and productive, play a crucial role in maintaining global bio-diversity and are of immense value to aquatic life as well as human-beings. Concentration of chlorophyll-a is a key indicator of the trophic status of these waters, which should be regularly monitored to ensure that their ecological balance is not disturbed. Remote Sensing is a powerful tool for this.

Reflectance models that are based on the red and near-infrared spectral channels of MODIS and MERIS satellites have been developed for estimating chlorophyll-a concentration. The results obtained from data collected by field spectrometers, airborne sensors, and space-borne sensors over inland, estuarine, and coastal waters from various geographic regions, with widely varying biophysical characteristics, show that the developed models have a very close and stable relationship with chlorophyll-a concentration, thereby precluding the need for re-parameterization of the models for each water body. Chlorophyll-a algorithms have been developed and calibrated, which have the potential for universal application to estimate chlorophyll-a concentration from satellite data routinely acquired over turbid and productive waters from around the globe.

Evaluation and Application of Predictive Habitat Modeling in Ecology - Justin Hoffman

  • Dissertation Defense
  • 4/21/2008

My dissertation research is an important contribution to the growing field of predictive habitat modeling in ecology. I investigate innovative approaches for evaluating the performance of different predictive habitat models and applying these methods to large scale ecological phenomena. Several predictive habitat models currently exist. It has been the focus of much research to determine which is the best model(s). However, much of this research is undermined by biased data sets. To resolve this issue, I tested model performance with simulated data that is not prone to the usual biases of real data sets. In general, my results support the findings of previous studies in that models that accurately predicted species distributions with real occurrence data also showed superior performance using simulated occurrence data. Using the conclusions from the model evaluation analysis as a basis, I applied these methods to two independent research questions. I first identified certain variables that best predicted the occurrence of chronic wasting disease (CWD) in Nebraska. Chronic wasting disease is a newly emerging infectious disease found only in members of the deer family (Family Cervidae). Analysis of several different combinations of spatial, temporal, and environmental variables showed that the chance of recording a positive CWD case was greater the more time spent sampling and when that sampling was conducted in western Nebraska. For the second question, I predicted range expansion among six North American mammals and ascertaining what role environmental variables have in predicting those expansions. I used two predictive habitat models combined with climate, land cover, and elevation variables to predict distributions. I predicted range expansions accurately for two of the six species, suggesting that other factors influenced the distributions of the remaining species. My results demonstrate the applicability of predictive habitat modeling in ecology and provide insights into novel methods of evaluating model performance.