Stephanie Graves

Cultural eutrophication, the excess input of nutrients by humans to waterbodies, is one of the biggest global threats to aquatic ecosystem health. The principal nutrients causing eutrophication are phosphorus (P) and nitrogen (N). Many human activities contribute N and P and effective management of eutrophication requires the identification of nutrient sources and their relative contributions to overall loading. This is difficult, because there can be several point and non-point sources in a single watershed. Thus, there is great interest in delineating relative sources of nutrients to improve management efforts. The first objective of this project is to test the effectiveness of novel stable isotopic tracers for identifying point and non-point sources of P and N. In this study, I will determine the relationship between nutrient inputs from non-point sources along a gradient of land use/land cover and δ18O-p, δ18O-n, and δ15N-n signatures in surface water to determine if these isotope tracers can predict anthropogenic sources of phosphate and nitrate. I will also determine the isotope signatures at known point sources to characterize these potential sources of N and P to the watershed. The second objective of this project is to establish a link between specific nutrient sources and harmful algal bloom (HAB) occurrence that will ultimately be used to inform the management of N and P inputs in the river. I will accomplish this objective by consolidating existing water quality data to understand spatial trends in nutrient dynamics and occurrence of HABs (measured as cyanobacterial toxins) within this watershed.