Nitrogen Flux in Watersheds: The Role of Soil Distributions in Nitrogen Flux to the Coastal Ecosystems

Quantifying the flux of nitrate from different landscape sources in watersheds is important to understand the increased flux of nitrogen to coastal ecosystems. The RiverNet program has measured the nitrate flux in the Neuse River Basin, NC on a 15 minute interval over the past ten years. Discharge and N flux in the basin also has significant inter-annual variations associated with El Nino oscillations modified by the North Atlantic oscillation. To understand how climate oscillations affect discharge and nutrient fluxes, we have continuously mapped nitrate concentrations, with Chlorophyll a and CDOM to understand how nitrogen is transported across landscapes to the coastal ecosystems. Hydric soil spatial distributions are an excellent predictor of nutrient transport in watersheds, and are related to the distribution of biogeochemical “hotspots”. Detailed spatial analysis indicates that nitrate, Chlorophyll a, and CDOM are not spatially coherent and one concentration cannot be used to predict the distribution of the other parameters as suggested by some regulatory agencies. These results also indicate that the contribution of wastewater treatment plants from urban watersheds has been greatly under-estimated in current models while the transport of agricultural nitrogen is controlled by hydric soil distributions and riparian buffer size. Prediction of future changes in discharge and nutrient flux by the modeling of climate oscillations has important implications for water resources policy and drought management for public policy and utility managers.