Deon Knights – NSF Postdoctoral Fellow – West Virginia University
The fate of nutrients in coastal freshwater systems: Examples from Wax Lake Delta and the Great Lakes
Nutrient inputs at coastal interfaces can be difficult to constrain where groundwater and river water mixes with ocean or lake water. My research aims at improving the assessment of nutrient loads in challenging coastal systems. In this talk, I discuss findings from two traditionally under monitored locations. I present estimates of groundwater discharge, a previously unaccounted source of nutrients, to the Great Lakes coast using high-resolution geospatial analysis. By integrating land use data, I also identify areas of the coast that are vulnerable to high nutrient loads from groundwater. In the second study, I use mesocosms to measure nitrate removal rates in a coastal wetland of Wax Lake Delta, Louisiana USA. Results suggest that summertime nitrate removal kinetics are highly correlated with a widely available remotely-sensed vegetation index (NDVI). Numerical simulations suggest that nitrate removal may be intrinsically limited in river-dominated deltas to a small fraction of the incoming nitrate load. From a management standpoint, nitrate removal efficiency can be improved by designing river diversions to build steeper deltas. However, manmade deltas alone cannot remove most nitrate discharging to the sea. Policy that addresses the nitrate load upstream is necessary to further reduce coastal nitrate loading.