Riverine N Flux, Atmospheric N Deposition and Links to Surface Water Quality on a Watershed Scale
Abstract
Identifying the sources of nitrate in watersheds is important to understand the increased flux of nitrogen to coastal ecosystems. Increasing nitrate contamination of surface water and groundwater is a problem in regions of intensive agriculture and in urban watersheds. The importance of atmospherically deposited N in watershed fluxes remains unknown. N flux in watersheds is event driven, and many ambient water quality monitoring programs do not have the temporal resolution to accurately calculate fluxes on watershed scales. The 15N and 18O composition of nitrate has been used to assess potential sources of nitrogen contamination and separate fertilizer nitrogen from atmospheric inputs. But because of transformations of nitrogen within the hydrological system, contaminant source tracing with nitrogen and oxygen isotopes has been complicated. We have used multiple isotope tracers of nitrate (15N, 17O, 18O) to distinguish between different N contamination sources, areas of extensive denitrification, and areas of atmospheric N deposition on the NC coastal plain and piedmont. Areas of extensive denitrification are associated with hydric soils and can be delineated with GIS distribution of hydric soils on watershed scales. The distribution of hydric soils may thus be an important element in prediction of environmental impacts of agriculture. Transport of atmospheric nitrogen into surface waters as indicated by the 17O of nitrate is event driven. Most discrete surface water samples have low concentrations of nitrate 17O, suggesting the importance of atmospheric N in riverine N flux has been overestimated in some studies. However, when the atmospheric N flux is integrated over a discharge event, atmospheric N can approach 25 - 30 % of the total N riverine flux in sub-basins with different land use. More work needs to be completed with multiple isotopic tracers and GIS analysis on watershed scales to quantify fluxes during hydrological events.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.H11I..05S
- Keywords:
-
- 0454 Isotopic composition and chemistry (1041;
- 4870);
- 0469 Nitrogen cycling;
- 1819 Geographic Information Systems (GIS);
- 1840 Hydrometeorology