HR: 17:30h
AN: B24A-07    [Abstracts]
TI: Nitrogen Flux in Watersheds: The Role of Atmospheric Deposition, Waste Water Treatment Plants and Climate Oscillations in Nitrogen Exported to the Coastal Ecosystems
AU: * Showers, W J
EM: w_showers@ncsu.edu
AF: North Carolina State University, Dept of MEAS Box 8208, Raleigh, NC 27695, United States
AU: Harris, J
EM: jon_harris@ncsu.edu
AF: North Carolina State University, Dept of MEAS Box 8208, Raleigh, NC 27695, United States
AU: Genna, B
EM: bjgenna@ncsu.edu
AF: North Carolina State University, Dept of MEAS Box 8208, Raleigh, NC 27695, United States
AB: Quantifying the flux of nitrate from different sources in watersheds is important to understand the increased flux of nitrogen to coastal ecosystems. Recent technological advances in chemical sensor networks has demonstrated that chemical variability in aquatic environments are chronically under-sampled, and that many chemical monitoring programs with monthly or daily sampling rates are inadequate to characterize the dominate seasonal, daily or semi-diurnal process and episodic storm event fluxes. The RiverNet program has measured the nitrate flux in the Neuse River Basin, NC on a 15 minute interval over the past six years. Significant diurnal variation has been observed in nitrate concentrations during high and low flow periods associated with waste water treatment plants in the basin. Other species of riverine nitrogen do not show this type of concentration variation. Comparison of 15 minute versus 24 hour nitrate flux calculations show that daily monitoring programs underestimate N flux by 10-40%. Two RiverNet stations were used to estimate nitrate gains in the river from biosolid application fields at one waste water treatment plant. Over a 4 year period non-point source nitrate entering the river from the fields was 50% of the nitrogen released in plant effluent. Non-point source flux from biosolid application fields is event driven and can not be determined from daily or weekly sampling. These results suggest that the importance of waste water treatment plant N flux has been under-estimated in current models. The δ¹⁵N and δ ¹⁸O composition of nitrate has been used to assess importance of atmospheric sources to watershed N flux, but because of transformations contaminant source tracing with these isotopes has been complicated. We have used multiple isotope tracers of nitrate δ ¹⁵N, Δ ¹⁷O, δ ¹⁸O to distinguish between different N contamination sources, areas of extensive denitrification, and areas of atmospheric N. Areas of extensive denitrification are associated with hydric soils and can be delineated with GIS distribution of hydric soils on watershed scales. Most discrete surface water samples have low concentrations of nitrate Δ ¹⁷O, suggesting the importance of atmospheric N in riverine N flux has been overestimated in some studies. Δ ¹⁷O of nitrate in groundwater is high in forested areas and low in agricultural areas. Nitrate Δ ¹⁷O have distinct peaks during storm events in forested and urban areas during falling discharge. When the atmospheric N flux is integrated over discharge events, atmospheric N can approach 30% of the total N riverine flux in urban areas. Discharge and N flux in the basin has significant inter- annual variations associated with El Nino oscillations modified by the North Atlantic oscillation. Positive JMA and NAO indexes are associated with increased groundwater levels and estuary fish kills. Future changes in these climate oscillations have important implications for water resources policy.
UR: http://rivernet.ncsu.edu
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0469 Nitrogen cycling
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0478 Pollution: urban, regional and global (0345, 4251)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting