Graduate Degree in Natural Resource Sciences

• Dissertation Defense
• 01/08/2025

The determination of the postmortem interval (PMI) is essential for the investigation and successful prosecution of suspected cases of homicide. While the forensic pathologist might be able to draw fairly accurate conclusions during the initial 24 – 36 hours, beyond this period, the assistance of other experts like forensic entomologists and forensic taphonomists would be required; in rare instances, forensic acarologists and palynologists might be invited. The present study was designed to observe the postmortem changes in Sus scrofa placed in cage in Nebraska, located in the American Central Great Plains. The setting is in an open grassland in late spring to early summer. The observed variables with respect to biotic and abiotic factors affecting the activities of necrophagous insects native to Nebraska, and the interplay between the environment and the carrion were studied. The result revealed delayed decomposition caused by late oviposition precipitated by low ambient temperature and rainfalls typical of the season, as well as the invasion of the carrion by Silphids and the attendant predatory action on the eggs and larvae of the necrophagous insects. These two factors are mainly responsible for the observed increase in the PMI. When the results are directly extrapolated to humans, it can be assumed that a decedent placed within the same taphonomic setting will start showing signs of skeletonization after 39 days of being deposited in the open grassland of the Central Great Plain.

• Thesis Defense
• 12/04/2024

The Photochemical Reflectance Index (PRI) provides an indicator of plant photoprotection under changing environmental conditions. PRI responds to photoprotection associated with the xanthophyll cycle and pigment pool size adjustments, and these represent distinct mechanisms regulating short- and long-term changes in photosynthesis. Consequently, PRI responses arise from a variety of factors, complicating the interpretation of the underlying photoprotective mechanisms associated with environmental change across species and functional types. This study aimed to assess the variation in photoprotective mechanisms within canopies of several deciduous and evergreen species over the 2023 growing season. We quantified species pigment responses by exposing dark-adapted leaves to high irradiance (“dark-to-light” method) while sampling reflectance to measure constitutive responses (PRI0) associated with photoprotective pigment investments and facultative responses (ΔPRI) representing the xanthophyll cycle. PRI was also measured in situ from canopies under high (“sun”) and low (“shade”) irradiance conditions to derive PRI-light responses, analogous to the dark-to-light method (PRI0 and ΔPRI). Evergreen species had lower PRI0 and ΔPRI values at mid-growing season, indicating greater constitutive investments in photoprotective pigments and less facultative xanthophyll cycle activity. In contrast, deciduous species had larger PRI0 and ΔPRI values, reflecting less constitutive investments but greater facultative xanthophyll cycle responses. Deciduous species had a larger seasonal PRI change compared to the more stable pigment responses of evergreen species. PRI in situ values were lower in high irradiance (“sun”) canopy positions than lower irradiance (“shade”) positions. Differences among functional groups were detected in low irradiance PRI in situ values, but not high irradiance PRI values. The patterns of facultative and constitutive pigment responses across seasons indicated variation in photoprotective mechanisms were distinct among deciduous and evergreen species having trade-offs in photosynthesis and photoprotection. PRI-light responses derived from canopy positions in contrasting irradiance conditions resembled differences detected among functional groups using the dark-to-light method. By separating facultative and constitutive PRI responses across conditions, species, and functional groups, these findings offer insights for understanding the diversity in photoprotection and presents a systematic sampling approach for understanding canopy PRI-light responses using proximal methods. These also provide further insight into recent PRI-light responses detected from airborne imaging spectrometry.

• Dissertation Defense
• 11/20/2024

Science and society are inseparably linked, shaping each other in ways that define our world. Recognizing the importance of teaching science for empowering students to take meaningful action toward building sustainable society, Vision III science literacy advocates bridging science education with civic and ethical responsibility, emphasizing the development of competencies that prepare citizens capable of addressing global challenges. Using controversial socio-scientific issues (SSI) as teaching context provides a valuable platform to develop such competencies, as these issues require students to analyze interdisciplinary evidence and consider the social, economic impacts of potential solutions. However, recognizing the unique perspectives individuals bring to the classroom is essential for tailoring effective instruction, particularly with controversial SSIs, as perspectives often shape learning, decision-making, and engagement. This study employed a qualitative approach to understand educators' needs for teaching complex SSIs, identifying areas for support, and exploring students' diverse perspectives on issues like climate change and equity. A constructivist grounded theory framework facilitated an in-depth exploration of these nuanced perspectives. This work highlights educators' lower confidence in teaching complex SSI and their need for targeted professional development. Also, undergraduate students’ learning of SSI concepts in a science literacy classroom context is described. An investigation was conducted of how students develop understanding of the connection between climate change and extreme flooding during an independent activity we designed to foster active learning. This instructional strategy may serve as a model for educators aiming to effectively teach controversial SSIs. Additionally, this study presents a framework illustrating individuals’ diverse approaches to equity in the context of complex, controversial SSI, encompassing perspectives from a narrow individual focus to a critical analysis of broader historical and systemic power dynamics. This framework offers educators a tool to assess students' perspective of equity, enabling the design of targeted interventions that foster deeper engagement with science issues embedded in social justice. Additionally, it may aid policymakers in understanding how individuals engage with equity dimensions in complex issues across various sectors, given its adaptable nature.

• Thesis Defense
• 07/24/2024

      Cyanobacterial Harmful Algal Blooms (CyanoHABs) detrimentally affect human, animal, and ecosystem health. Remotely sensed early warning systems for algal blooms in inland lakes could contribute to more proactive water quality monitoring and help mitigate negative impacts. Advances in freely available remote sensing imagery, with finer spatial, temporal, and spectral resolutions, present new opportunities for the development and comparative analysis of methods to detect sudden deterioration in lake water quality. In this thesis, I compared and tested for temporal and spatial early warning signals of CyanoHABs in field-based and remotely sensed datasets from 2019 to 2023 in Pawnee Lake in southeast Nebraska, U.S.A. Field data consisted of biweekly microcystin (MC) levels from the Nebraska Department of Environment and Energy’s Beach Watch Dataset and remotely sensed data consisted of two-week Normalized Difference Chlorophyll Index (NDCI) composites from the Sentinel 2B surface reflectance satellite. In Chapter 1, I tested for rising variance in biweekly MC and NDCI time series from May-September of each year at three rolling window sizes. I also computed the correlation between MC and mean lake wide NDCI and examined within year trends in each variable. Both MC and NDCI tended to increase from May-September of each year and the relationship between MC and NDCI approached statistical significance (p=0.06) but rising variance did not provide early warning of documented CyanoHAB events for either variable. In the second chapter, with a landscape ecology-based approach, I computed the number of high-NDCI patches (i.e., contiguous pixels with elevated NDCI values) within Pawnee Lake, computed the correlation between MC and the high-NDCI patch count, and tested for rising variance in high-NDCI patch count at three rolling window sizes. Although both MC and high-NDCI patch count tended to increase from May – September of each year, I found no relationship between MC and high-NDCI patch count and no evidence of early warning of documented CyanoHABs. Reasons for the lack of advanced warning could include small seasonal sample sizes and insufficient temporal resolution in both the field- and remotely sensed observations, examination of only a subset of temporal and spatial early warning indicators and limited geographic scope. This study provides a baseline for guiding future analyses with higher-resolution observations and alternative metrics and locations.

• Thesis Defense
• 06/28/2024

Understanding and conserving ecological connectivity is critical to the preservation of vulnerable landscapes. Circuit theory, in which landscapes are imagined as circuit boards with varying resistances to the flow of current, is being increasingly used to model spatially explicit connectivity of landscapes and to inform land management and conservation decision-making. Utilizing continuous, quantitative estimates of percent cover by five land cover functional groups to create a conductance surface, this study expanded upon an established application of circuit theory that used the open-source software Circuitscape to model species-agnostic, omnidirectional connectivity. This model was automated using Python to create time-series connectivity maps from which comparisons could be made across time to assess pre- and postfire land cover patterns across the landscape. By applying this methodology to a U.S. Great Plains landscape affected by a large wildfire in 2012, this study found that for most functional land cover types, spatial configurations of areas of high and low connectivity changed in response to the wildfire disturbance, but quickly returned to pre-fire conditions. Exceptions were the tree and shrub functional groups, which saw persistent patterns of decreased connectivity in areas that were burned. This approach to modeling landscape connectivity over time could further enhance circuit theory-based assessments of landscapes affected by wildfire and tools for land managers promoting functional connectivity and resiliency in those landscapes.

• Dissertation Defense
• 05/08/2024

Drought is a complex phenomenon with varying degrees of impacts and monitoring methods. No drought is alike, creating a challenge for both water managers and communities. No area is immune to a drought. Due to the cyclical nature of drought events, clear information to those impacted is necessary to reduce risk and move towards proactive responses, as opposed to reactive responses. To better provide communication and mitigation tools, Drought Early Warning Information Systems (DEWIS) have been developed in various regions and contexts. To improve early warning, an understanding of the end user’s perceptions of risk, and the applicability of data and methods is valuable. This dissertation discusses findings from three related studies exploring the use of multiple methods and streams of data for drought risk in the United States. Chapter 1 provides a brief overview and outline of this dissertation. Chapter 2 presents findings from a study looking at the perceptions and usage of the term ‘flash drought’ among water managers in the United States. Chapter 3 is focused on modelling methods of using crop insurance occurrence data as a proxy of drought impacts for specialty crops. Chapter 4 is a systematic literature review of the use of mixed methods in drought science. Chapter 5 is the final study that investigates the benefits and validation of mixed methods in understanding drought risk to dry beans in North Dakota and Minnesota. Finally, in Chapter 6, I provide a brief conclusion of the findings and areas for future research. This dissertation demonstrates the use of various data types in understanding drought risk for improving drought early warning systems.

• Thesis Defense
• 04/19/2024

Piping plovers (Charadrius melodus; hereafter plovers) and interior least terns (Sternula antillarum athalassos; hereafter terns) are two avian species that nest along the Lower Platte River system (LPRS) in Nebraska. Natural nesting habitat for both species consists of sparsely vegetated expanses of sand near water. In the LPRS, river sandbars provide natural nesting habitat for plovers and terns. Sandbar habitat has been reduced from historical availability due to anthropogenic modifications and annually variable depending on hydrological fluctuations. Plovers and terns in the LPRS also nest at off-river sites, such as sand and gravel mines and their derivatives, transition sites and lakeshore housing developments. Off-river sites provide most of nesting habitat in the LPRS when sandbar habitat is scarce and are presumed to be important for the persistence of plovers and terns in the LPRS. However, the quantity of plover and tern nesting habitat provided by off-river sites is not self-sustaining and predicted to decline due to changing sand and gravel mining industry practices. Understanding the vital rates of plovers and terns in the LPRS will inform the role that off-river sites hold in the future conservation and long-term persistence of both species. To contribute to this understanding, I assessed consequences of off-river nesting between sandbars and off-river sites and among off-river site types using a long-term monitoring database collected by the Tern and Plover Conservation Partnership from 2008-2023. I also investigated additional factors that could affect vital rates such as the timing of nest initiation and hatching, extreme temperatures, conspecific and heterospecific nesting proximity, and nest exclosure usage (plovers only). For plovers, I evaluated annual and intra-seasonal adult survival, annual hatch-year survival, pre-fledging chick survival, and pre-fledging chick growth rates at off-river sites, and nest survival at off-river sites and sandbars. For terns, I evaluated pre-fledging chick growth rates and nest survival at off-river sites and sandbars. I did not find evidence for a difference between off-river sites and sandbars in nest survival for either species or for tern chick growth. Among off-river sites, plover chick growth was greatest at housing sites and tern chick growth was greatest at mine sites. There was no evidence that hatch date affected growth of plover chicks, but later hatched tern chicks had greater growth. Nest survival for plovers did not differ among off-river sites but was greatest at housing sites for terns. For both species, nest survival increased with increasing proximity to tern nests, greater proportion of incubation days with ambient temperatures above mean high temperatures, increasing nest age, and decreasing nest initiation date. Exclosed plover nests had higher survival. There was no evidence to show a difference in survival for adult plovers with exclosed nests. Plover adult, hatch-year, and chick survival was comparable to estimates of other populations. These results demonstrate the dynamics of plovers and terns in the LPRS and the importance of off-river habitat for the persistence of plovers and terns in the LPRS. Specifically, the lack of evidence for a demographic consequence of off-river nesting to nest survival or tern chick growth suggests that off-river habitat may support plovers and terns similarly to river sandbars. Furthermore, prioritization of early season nests may be most efficient for conservation and management resources, however tern chicks may benefit from investment later in the breeding season. As nesting near terns may improve plover nest success, measures to protect terns may also benefit plovers. Additionally, continued use of nest exclosures may improve nest success for plovers with limited effects to adult survival. Continued monitoring and study of plovers and terns at off-river sites and sandbars, particularly in the face of changing climatic and industry conditions, will further support the persistence of these species in the LPRS.

• Thesis Defense
• 12/05/2023

Long-term and excessive fertilizer application has continuously increased nitrate in the vadose zone-groundwater integrated system. Nitrate, a highly miscible and mobile inorganic nitrogen species, leaches through the vadose zone to groundwater, posing human health implications when continuously consumed. Our study aims to evaluate the redox-based transformation of inorganic nitrogen species in a vadose zone under a row-cropped, sprinkler-irrigated field in central Nebraska. Undisturbed sections of deep vadose zone cores were packed in the columns representing the entire vadose zone, and a groundwater table was simulated. The biweekly collected porewater and sediment representative samples were analyzed for nitrate-N and ammonia-N transformations. We found that the average ammonia-N concentrations under rainfed were significantly higher than in sprinkler-irrigated system and pre-experimental soil (p.value <0.05). Pre-experimental soil nitrate concentrations were significantly higher than rainfed and sprinkler - irrigated systems (p.value < 0.05). In biweekly extracted porewater, simulation beneath the sprinkler-irrigation has significantly higher NO3-N levels in the root zone than the rainfed system porewater (p.value < 0.05). Still, no significant difference was observed at the capillary fringe. On the other hand, porewater NH4-N concentrations in the rainfed root zone were significantly higher than in the sprinkler-irrigated root zone, with comparable concentrations in the capillary fringe. Interestingly, in sprinkler-irrigated, the groundwater-irrigated system had higher NH4-N levels than the rainfed system, whereas the NO3-N concentrations were comparable in both irrigation systems. Our study suggests that differences in water volume input can impact nitrate transformation in the vadose zone.

• Thesis Defense
• 11/29/2023

The Nebraska Water Quality Index, under development by the Nebraska Department of Environment and Energy, summarizes in a single value eight environmental parameters that have been regularly monitored in Nebraska for nearly 20 years. The water quality parameters used in the Nebraska Water Quality Index have been shown in previous studies to be critical to bacterial growth. As such, this index has the potential to correlate with the microbial community in freshwater systems. Here, I relate the Nebraska Water Quality Index to lotic microbiome composition and structure using 16S rRNA gene amplicon sequence data collected from the North Platte River Basin, Nebraska. Gini-Simpson alpha diversity was significantly negatively correlated with Nebraska Water Quality Index ratings, as were the relative abundances of several bacterial orders: Absconditabacteriales, Burkholderiales, Campylobacterales,Oscillospirales, Rhizobiales, and Vicinamibacteria Subgroup 17. Nebraska Water Quality Index ratings were positively correlated with Flavobacteriales and Saccharimonadales. Analysis of environmental parameters suggested that total nitrogen played a substantial role in shaping the microbial community and water quality. The Nebraska Water Quality Index is a convenient method of summarizing the physiochemical parameters of a stream environment to monitor spatiotemporal trends in water quality and gauge the success of ecosystem restoration efforts. Analysis of the aquatic microbial community in conjunction with the Nebraska Water Quality Index may help identify the cause of water quality problems. For instance, Oscillospirales is associated with fresh cattle manure. The presence of Oscillospirales in areas of low Nebraska Water Quality Index Ratings could help users identify sources of cattle manure pollution

• Thesis Defense
• 11/20/2023

Climate change together with the increase in demands for food, feed, fuel, and fiber are becoming a threat to sustainability and resilience of agriculture and pasture lands. Bromus inermis (smooth bromegrass) dominates pastures for cattle grazing in Eastern Nebraska, US, where it is planted in monocultures, and is considered high quality forage because of its palatability and high nutritional value, especially under intensive management practices. Sustainable management of these pastures is key to long-term resilience. This study aims to assess the performance of smooth bromegrass pastures to the combined effects of long-term management practices (since 2005) of fertilization with Supplemental Dry Distiller Grain Soluble (DDGS, Fertilizer-SF), mineral (Fertilizer-HF), or control (no fertilizer-CG), under both rotational grazing and no grazing treatments or true control (no-grazing and no-fertilizer). Soil characteristics, plant morphology (biomass, leaf area index, and specific leaf area), forage quality (acid detergent fiber, neutral detergent fiber, and crude protein), plant physiology (chlorophyll content and fluorescence), and vegetation optical properties (multispectral leaf reflectance) were measured throughout the growing season in 2022. Results showed that 2022 experienced drought with precipitation being (42 %) lower than the long-term average for the site. Pasture productivity was affected by fertilization treatments, grazing and water availability. We did not observe differences between fertilization treatments (SF and HF), where both treatments showed similar morphological and physiological trends throughout the season and differed significantly from control. These results are consistent with previous work, supporting the use of DDGS as an alternative to mineral fertilizer, thus reducing nitrate leaching and runoff from the system. Rotational grazing resulted in lower biomass and leaf area index (LAI) compared to ungrazed pastures, and higher crude protein. Several Indices (Normalized Difference Vegetation Index-NDVI, Chlorophyll Index red edge-CIre, and Vogelmann Red Edge Index-VRE) were tested as a non-invasive approach for vegetation assessment. The three vegetation indices showed significant relationship with ground measurements, demonstrating the feasibility of proximal sensing to measure different biophysical traits under different management practices and environments. HF and to a lesser extent SF resulted in improved growth conditions early in the season relative to controls, which provided a slight advantage to these treatments in a drought year over non-fertilized treatments, under both grazed and ungrazed conditions. Results from this study build on previous research on the site, and serve in the development of sustainable climate smart and adaptive management practices and contribute to land management policy planning.

• Thesis Defense
• 11/17/2023

The presence and spread of invasive species have changed the way humans interact with their environment. Invasive bigheaded carp are well established throughout the Missouri River system below Gavin’s Point Dam. Nebraska and South Dakota co-manage a popular recreation paddlefish fishery, operating a snagging season (October) and an archery season (June). Satisfaction of recreational paddlefish fishers depends on many factors that may be influenced by the presence of invasive species. We used comment cards (1997-2021), mail surveys (2022), and onsite surveys (2022 and 2023) to assess the influences of bigheaded carp on paddlefish fishers’ satisfactions. Based on a content analysis of comment cards and importance grid analyses of mail and onsite surveys, we determined that bigheaded carp were not influencing paddlefish fishers’ satisfactions. Factors identified as influencing paddlefish fishers’ satisfactions were related to the catch of paddlefish. Contrary to our expectations, we documented no influence (positive or negative) of invasive species on satisfactions of recreational paddlefish fishers. Further work with other invasive species and other recreational users is needed to determine whether our findings are more broadly applicable.

• Thesis Defense
• 11/15/2023

Recreational fishing is one of the world's most popular pastimes, wherein participation is associated with sociodemographic factors. Even so, fishing license sales are declining in the USA in conjunction with a reduction in rural populations as people move to urban areas. Thus, urban areas are constantly growing in population size, population diversity, and geographic size suggesting a need to understand fishing participation in these growing areas. Natural resource managers often use participation to understand recreationists, yet avidity could provide a new way to understand recreationists. The goal of our study is to understand what sociodemographic factors influence the fishing avidity of urban anglers and what relationships exist between fishing avidity and other recreational-activity avidities of anglers who reside in urban environments. Specifically, we asked: 1) do Esri Demographics’ urbanization groups better predict fishing avidity of anglers within an urban setting than sociodemographic factors typically gathered in surveys, and 2) what relationships (positive and negative) exist among avidities of recreational activities for fishing-license holders within an urban environment? We created generalized linear models and used an information theoretic approach to evaluate influences of sociodemographic factors on fishing avidity, and we used Principal Component Analysis to evaluate relationships among avidities of recreational activities. We sent the 2020 Omaha Recreation Survey to a random subset population of 2019 fishing-license holders that resided within the four urbanization groups of Omaha, Nebraska, as designated by Esri Demographics. We determined that Esri Demographics’ urbanization groups did not predict fishing avidity better than a priori models of common sociodemographic factors. We report a weighted average model of sociodemographic factors (i.e., employment, sex, household size, household gross income, education, R3 retained, R3 reactivated, day license holder, multi-year license holder, additional fishing members in the household, and age) to predict fishing avidity for individuals residing in urban environments. No recreational-activity avidity has a strong negative relationship with fishing avidity. Recreational fishing avidity has strong positive relationships with avidities of ice fishing, hunting, and golf. Our study provides new understanding of how urban anglers recreate in urban environments throughout the USA, which could aid management agencies with development of avidity thresholds to categorize anglers, explore opportunities for co-development of recreational activities for anglers, and identify targets of fishing effort.

• Dissertation Defense
• 06/08/2023

Research, management, and modeling for water quality and resources, ecological processes, agricultural and urban planning, wildlife habitat, and much more depend on accurate water level and discharge measurement. Greater and more complex water resource needs for parties with competing interests demand more detailed models and effective science communication than are possible with the traditional scalar measurements. The scientific community recognizes the need for new methods that provide context for manual and programmatic extraction of a broader range information to make measurements and predictions, drive insights and facilitate communication between stakeholders and the public. Methods have been developed to accurately measure water level in ground-based imagery, but it is critical to improve those methods and create standardized tools, workflows, and software for use by the scientific community, academia, and industry. The purpose of this research was to find ways to develop and analyze tools and methods to measure and/or predict water level and streamflow in images with less artificial conditioning of the water scene than was previously possible. Three research studies were identified to accomplish this: 1) A site study to determine whether it is possible to predict water level and streamflow accurately to fill data gaps in United States Geological Survey historical data from a time-series of images with no artificial calibration or waterline target in the scene, 2) creation of a free, open-source software suitable for use by hydrologists and ecologiststo measure water level in images with a pixel to world coordinate calibration and waterline search target installed in a stream or river, and 3) creation of a new calibration target that improved the bow-tie calibration target and measurement surface used in #2 by allowing for calibration in every image and that occluded less of the scene allowing for improved contextual analysis.

• Oral Presentation
• 04/26/2023

Greenways are nature’s infrastructure– offering transportation of plants, animals and insects, as well as places of study, survival and solace for people. The Salt Valley Greenways weave through and around the city of Lincoln, connecting the natural and rural world into the bustle of urban life. This storytelling project explores the diversity of resources that greenspaces provide and reveals those through conversation with scientists, artists, and folks who call Lincoln home.

• Thesis Defense
• 04/19/2023

Rangelands are important ecologically, economically, historically, and socially. Rangelands are also threatened by regime shifts (state transitions) like woody encroachment, desertification, and exotic annual grass invasion. Management of rangelands to prevent, contain, and reverse regime shifts relies on rangeland monitoring. Innovations in rangeland monitoring—such as the generation of new landcover datasets with field data, remote sensing, and geospatial cloud computing—allow for earlier detection (screening) of regime shifts in support of proactive rangeland management. In this thesis, I screened Nebraska landscapes for woody encroachment, desertification, and exotic annual grass invasion, according to three characteristics of regime shift signals: presence, persistence, and non-stationarity. In addition to informing management, results can help advance approaches to regime shift screening in rangelands.