My research integrates the fields of microbial ecology, biogeochemistry and aquatic ecosystem ecology. I use tools from analytical chemistry, microbiology and molecular biology to better understand how microbes control ecosystem-level nutrient fluxes. Questions asked in my research program have valuable connections to current environmental concerns including global change, the effects of land-use change on ecosystems and aquatic eutrophication. My research focuses on nitrogen (N) cycling. Excessive N causes many water-quality problems. Much of the N that enters watersheds is removed before reaching the oceans, but how and where the removal occurs is not well understood.
I began teaching Limnology for SNR in spring of 2012. In the past, I have taught classes on global biogeochemical cycles, environmental microbiology and, wetlands and global change.
The field of biogeochemistry appeals to me intellectually because of the inherent connectedness between disciplines. The term denotes an exploration of the ways the physical, chemical and biological realms are related with the goal of understanding the complexity of a fully integrated system. Linking concepts and disciplines together takes away some of the simplicity of how we understand them by themselves, but allows us to grasp a larger view of the world. Learning is also a process that makes connections between two areas that formerly were unrelated, thereby giving the person a deeper understanding of his or her surroundings. My main goal in my teaching is to aid students in making connections between seemingly different disciplines, as well as to connect science into their personal lives. By helping them see the vast array of connectedness in our world, I empower students to acquire knowledge on their own and transition from receivers of information into life-long learners.
Please see my website for more information on my field work and lab, and how students can be involved.
My training and research encompasses three related themes:
- Microbial Coupling of Elemental Cycles (Environmental Microbiology)
I am interested in how microbial metabolism can link elemental cycles. A well-known example of this is denitrification, a microbial pathway that links the carbon (C) and N cycles. In a less-studied example, microbes replace C with sulphur (S), thus linking the N and S cycles. My dissertation research found N-S coupling is widespread in freshwaters. This connection between the S and N cycles was surprising because S is often considered insignificant in freshwaters. Because of my work on the topic, I was asked to participate on an NSF proposal to investigate C, N and S coupling in a coastal wetland experiencing salt-water intrusion. Understanding potential changes in coupled elemental cycles will be critical for
predicting how fragile coastal wetlands will respond to sea level rise.
- Alternative Pathways of N Cycling in Freshwater Ecosystems (Biogeochemistry)
Through the discovery of freshwater N and S coupled cycling, I became interested in other understudied N cycling processes, including dissimilatory nitrate reduction to ammonium (DNRA) and anaerobic ammonium oxidation (anammox). Most textbook diagrams of the N cycle do not include DNRA or anammox; this omission maybe because the pathways are insignificant, or may be because we don't yet know when and where they are important. My dissertation found that DNRA is a significant N cycling pathway in wetland ecosystems. Understanding DNRA has profound implications for our knowledge of N cycling because the process converts nitrate to biologically available ammonium, and therefore may further enhance eutrophication problems.
- Landscape Controls on N Cycling across Aquatic-Terrestrial Interfaces (Ecosystems)
Microbial communities perform the N cycling processes described above. Those communities, however, are organized by abiotic factors. I am also interested in how landscape-level variation in key abiotic factors affects biogeochemical cycling. As a postdoc I examined how O2 variation in riparian buffers affected denitrification rates. O2 is rarely measured in soils and is a key regulator of microbial functions, including denitrification. O2 variation is currently missing from terrestrial biogeochemical models that consider soils to be uniformly oxic. This omission represents a gap in our knowledge of the controls on nutrient cycling, particularly for ecosystems that are both terrestrial and aquatic (e.g., wetlands). I am continuing this work by exploring the connections between water table dynamics, soil O2 fluctuations, and greenhouse gas production (CO2, CH4, N2O) in an agricultural field being restored to a wetland. This work is funded with a grant from the U.S. Department of Agriculture and NASA's joint program on Carbon Cycle Science.
My research program evaluates the importance of microbial processes in an ecosystem context, bridging the gap between lab-based studies of microbiology and ecosystem flux studies. I pursue mechanistic questions that span the basic-applied spectrum, and bridge my three sub-disciplines. Integrative questions such as these are aligned with the research priorities of NSF (DEB-Ecosystems), the USDA and the EPA.