Hosted by US Environmental Protection Agency
1. Linking Aquatic Invertebrate δ15N with Watershed N Reduction Processes Across the U.S.
Total nitrogen (N) concentration is a significant stressor to U.S. waterways. Aquatic N concentrations are strongly related to the amount of N added to a watershed, but concentrations can vary widely, even with the same rate of inputs. EPA developed a tool to understand why some watersheds have lower aquatic N concentrations than others when the N applied to the landscape is the same. Using data from EPA’s National Aquatic Resource Surveys (NARS), National Nutrient Inventory (NNI), and stable isotopes of N measured in aquatic insects, the tool can identify watersheds that are efficient at denitrification. Results from this analysis will help promote effective ways to reduce excess N entering surface waters.
Presenter: Renee Brooks, EPA Office of Research and Development
J. Renee Brooks is a Research Scientist with EPA's Pacific Ecological Systems Division (PESD) in Corvallis Oregon. She is the science lead for PESD's Integrated Stable Isotope Research Facility and specializes in applying measurements of stable isotope ratios and theory to help solve environmental issues central to EPA's mission for clean water for everyone.
2. δ15N Reflects Wetland Nitrogen Processing on a National Scale as Predicted by Soil Chemistry Stoichiometry
Wetlands provide critical ecosystem services by intercepting and retaining excess non-point nitrogen (N) inputs moving through the environment. However, not all wetlands have the same capacity to store and remove N. Historic denitrification across the continuous U.S. has been identified using N stable isotopes in wetland soils and soil chemistry stoichiometry. This method builds on our understanding of nitrogen processing in wetland soils and increases our ability to identify wetlands that are efficient at preforming this critical ecosystem service. This study can be used to inform nutrient reduction strategies at watershed scales.
Presenter: Catherine Nowakowski, EPA Office of Research and Development
Catherine (Catrina) Nowakowski is an ORISE Postdoc at the US EPA's ORD Office in Corvallis Oregon working with Renee Brooks, Amanda Nahlik, and Jana Compton on nitrogen processing in wetlands. She is an isotope ecologist that works across terrestrial and oceanographic ecosystems. She received her Ph.D. in Oceanography at the University of Rhode Island and a Bachelor's degree in Environmental Engineering at the University of Connecticut.
3. Deciphering Patterns in Whole Fish Nitrogen Isotopes on a Continental Scale
Nitrogen isotopes are often used as an indicator of anthropogenic nitrogen loading. This study analyzed estuarine fish collected by EPA’s National Coastal Condition Assessment (NCCA) for isotopes of nitrogen and carbon. Water quality, nutrients, chlorophyll, and sediment chemistry data, along with fish life history and watershed land use, were used to examine how whole fish δ15N was related to these environmental variables using random forest regression at the national and ecoregional scale. Though work is ongoing, the study identifies continental scale patterns that can be used to inform local or regional research using stable isotopes.
Presenter: Peg Pelletier, EPA Office of Research and Development
Marguerite (Peg) Pelletier is an estuarine ecologist working at the EPA's Office of Research and Development lab in Narragansett, RI. She received her Ph.D. from the University of Rhode Island and is currently the ORD coastal benthic lead for NARS (NCCA). Her research has focused on indicator development to improve environmental assessment, assessment of multiple stressor impacts on estuarine ecosystems, and the use of statistical and multivariate tools to better understand marine and estuarine response to environmental stressors.