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Sensitivity Analysis of SWAT Nitrogen Simulations with and without In-Stream Processes
Citation:
Yuan, Y. AND L. Chiang. Sensitivity Analysis of SWAT Nitrogen Simulations with and without In-Stream Processes. AGRONOMY JOURNAL. American Society of Agronomy, MADISON, WI, 61(7):969-987, (2015).
Impact/Purpose:
When in-stream processes were simulated, the annual average dissolved N losses had little or no changes from different fertilizer application timing and amount. Compared with the monthly observed N losses, the SWAT-simulated N losses with in-stream processes had lower dissolved N, but higher organic N and TN losses. Based on the sensitivity results, dissolved N losses could be adjusted by increasing the value of ERORGN or SOLORGN. However, this would also increase organic N and TN losses. Conflicts such as these demonstrated the importance of further evaluating SWAT’s simulation of in-stream processes.
Description:
Nitrogen (N) losses to surface waters are of great concern on both national and regional scales. Scientists have concluded that large areas of hypoxia in the northern Gulf of Mexico are due to excessive nutrients derived primarily from agricultural runoff via the Mississippi River (Rabalais et al., 1996, 1999; McIsaac et al., 2001; Aulenbach et al., 2007; USEPA Science Advisory Board, 2007). Loss of N to surface waters is also a problem on a local level. Excess nitrate in drinking water can be toxic to humans, and treatment is expensive when nitrate in surface water supplies exceed EPA threshold levels (USEPA, 2008). Therefore, agencies such as the United States Department of Agriculture (USDA)-Natural Resources Conservation Services (NRCS) have recommended the implementation of conservation practices including the reduction of N fertilization rates and creation of wetlands and riparian buffers (Mitsch et al., 2001; Crumpton et al., 2007) to reduce N losses to waterbodies. Quantifying the impact of those conservation practices on N losses is critical for achieving the maximum environmental benefit.