Abstract: Stable isotope ratios can act as tracers in environmental systems. Nitrate isotope ratios can differentiate the system's dominant sources, particularly synthetic fertilizer, manure, and atmospheric nitrate via precipitation. In this study, we utilize the stable isotope ratios of nitrate (δ15NNO3- and δ18O NO3-) in a local karst-influenced watershed to constrain the sources and flow paths of nutrients during a range of precipitation events.
Preliminary results of storm event nitrate isotope ratios show the significant influence of precipitation on nitrate isotopic compositions. We observe more positive δ15N and δ18O values during a storm event compared to baseline conditions. Storm δ15N values suggest a predominant contribution from agricultural runoff, likely mobilized by increased surface flow and infiltration. Concurrently, δ18O values indicated an influx of atmospheric nitrate from direct precipitation and rapid surface runoff. These shifts in isotope signatures during storm events support a blending of sources via dynamic mixing.
Additionally, new methods for isotope ratio measurement will be presented. The Orbitrap high resolution mass spectrometer has been recently reconfigured with a focus on isotope ratio measurements. This technology opens up the possibility of “easy” measurement of rare and clumped isotope species, tracking bacterial processes, temperature relationships, and tracing the fate of degradation products. A brief introduction and possible avenues for future collaborations will be explored.
Bio: Dr. Erhardt started as an Environmental Engineer at Northwestern University, discovering geology her senior year. After working as an engineer on acid mine drainage remediation, she returned to graduate school for an M.S. from the Colorado School of Mines and a PhD from Stanford University focused on isotope geochemistry. After three years at the University of Cambridge as a CIFAR postdoctoral fellow, she has been at the University of Kentucky since 2016. Additionally, she is an Anna Boysken Fellow for the Institute for Advanced Study and was a Global Visiting Professor with the Institute of Analytical and Water Chemistry at the Technical University of Munich. She is the director of the Kentucky Stable Isotope Geochemistry Laboratory, focused on isotope analysis of carbon, nitrogen, hydrogen, oxygen, and sulfur isotopes in a wide range of geologic and environmental samples.