A GIS Assessment to Identify and Reduce Nitrate Loads That Contribute to Hypoxia In the Gulf of Mexico.

Nitrate leaching has been reported as one of the main pathways contributing to the nitrate flux out of the Mississippi River watershed into the Gulf of Mexico. This out-flux of nitrogen has been identified as one of the factors that contribute to the hypoxia problem in the Gulf of Mexico. The Arkansas Delta is a key productive agricultural region of the Mississippi River watershed, and it has been reported that while it is not as large as other agricultural areas of the Midwest that are more susceptible because of their tile drainage, the Arkansas Delta still contributes nitrates to the out-flux of the Mississippi River watershed via leaching losses. The new Nitrogen Loss and Environmental Assessment Package with GIS capabilities (NLEAP-GIS) was used to assess the spatial and temporal variability of these leaching losses on selected farm areas for different counties. Although the analysis did not include the entire watershed of the Arkansas Delta, we suggest that this GIS analysis for different farm fields can be used to help us assess the benefits of implementing best management practices (BMPs) across selected counties for the study. Maximum potential loads for nitrate leaching were estimated by conducting an assessment across corn-soybean and cotton rotations when high nitrogen rates were applied. An analysis was then conducted at the same locations using BMPs, and the potential reduction in nitrate loads was assessed. Additionally, to support this GIS assessment, calibration and validation studies were conducted from 2008 to 2009 for three selected farms. This long-term GIS analysis shows, among other preliminary findings, that rotations of soybeans into corn systems significantly reduces emissions of N₂O across this region and reduces NO₃-N leaching losses at the field level. Results from improvement in method, time and rate of nitrogen applications will also be presented.