1. The Study of Excess Nitrogen in the Neuse River Basin

1. 1. The Study of Excess Nitrogen in the Neuse River Basin • “A Landscape Level Analysis of Potential Excess Nitrogen in East-Central North Carolina, USA” • Paper by C.T. Garten Jr. and T.L. Ashwood. 2003. Water, Air, and Soil Pollution, 146. (1-4): 3-21 • Presented by Harrison Miller, Environmental Studies, Geog 370, 26 February 2008

2. 2. Assessment of potential excess nitrogen under different land cover categories • Problem: Excess nitrogen (N) contributes to aquatic eutrophication (excessive nutrients in a body of water that cause various problems) and elevated concentrations of nitrate in ground water. This study attempted to understand the distribution, the determinants, and the seasonality of potential excess N in terrestrial ecostystems at the landscape scale. • Hypothesis: If N inputs exceed N outputs, then the difference represents N at risk of loss from the landscape to surface receiving waters and groundwaters.

3. 3. Methods • 1.) Acquistition of land cover data from remote sensing • 2.)Development of a mass balance model to quantify potential excess N unders different land covers • 3.) Estimation of N fluxes under different land covers based on literature reviews • 4.) Calculation of potential excess N on a seasonal basis in the Neuse River Basin

4. 4. Results • N uptake by crops, herbaceous vegation (grasses), and herbaceous wetlands were similar and greater than the median value of N uptakes by forests. • Differences between rates of net N mineralization in forest and grassland soils were statistically significant. • Forest ecosystems are weak N sinks whereas wetlands are strong N sinks. • The highest rates of soil N mineralization and denitrification were concentrated in areas bordering streams of the Neuse River. • The potential excess N in the Neuse River Basin is most influenced by spatial and temporal variation in fertilization and net soil mineralization.

5. 5. Conclusions • Large areas of land in the Neuse River Basin are borderline in potential excess N. Such areas could not be classified as either N sources or N sinks because the estimated N budget was in balance. However, with future changes in land use, these sensitive areas could become N sources and N sinks. • At the landscape scale, the timing of N inputs (i.e. spreading fertilizer) and outputs are an important determinant of potential excess N. • Potential excess N on the landscape is highest in spring and summer. • The seasonal patterns in N loads in the Neuse River depends on location. Annual N fluxes at stream monitoring stations vary considerably, depending on the year.

6. Criticisms • The model used in this study does not distinguish between soil ammonium and nitrate. The model also assumed that all excess N is at risk of export from the landscape. These assumptions are problematic because they will overestimate N loads to surface receiving waters because nitrate is more readily leached from soil than ammonium. • The model does not distinguish between different chemical forms of N and it does not discuss hydrologic transport of N. • Measures of N export in rivers and streams may not be the best way to determine how well the model predicts potential excess N at the landscape scale. The in-stream loss of N exports from the ground can be substantial. Some studies find that the terrestrial landscape retains most of the N imported to the Neuse River Basin or that it is removed by processes occurring naturally in the river.