Nutrient delivery from the Mississippi River to the Gulf of Mexico and effects of cropland conservation

Authors: White, Michael; SANTHI, CHINNASAMY - Texas Agrilife Research; KANNAN, N - Texas Agrilife Research; Arnold, Jeffrey; Harmel, Daren; NORFLEET, LEE - Natural Resources Conservation Service (NRCS, USDA); ALLEN, PETER - Baylor University; DILUZIO, MAURO - Texas Agrilife Research; WANG, XIUYING - Texas Agrilife Research; ATWOOD, J - Natural Resources Conservation Service (NRCS, USDA); HANEY, E - Texas Agrilife Research; JOHNSON, M - Natural Resources Conservation Service (NRCS, USDA)

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2013
Publication Date: 1/1/2014
Citation: White, M.J., Santhi, C., Kannan, N., Arnold, J.G., Harmel, R.D., Norfleet, L., Allen, P., Diluzio, M., Wang, X., Atwood, J.G., Haney, E., Johnson, M.V. 2014. Nutrient delivery from the Mississippi River to the Gulf of Mexico and effects of cropland conservation. Journal of Soil and Water Conservation. 69(1):26-40.

Interpretive Summary: Excessive nutrients transported from the Mississippi River Basin have created a dead zone in the Gulf of Mexico. The USDA Conservation Effects Assessment Project (CEAP) used simulation models to predict nutrient sources and delivery to the Gulf. We predict that cultivated cropland is the dominant source of nutrients in both local waters and the Gulf. Urban nonpoint sources and municipal and industrial dischargers are also significant contributors. The Upper Mississippi, Lower Mississippi, and Ohio Basins are the dominant regional sources of nutrients. Approximately 90% of the nutrients lost from sources near the Mississippi River’s main stem reach the Gulf. The establishment of conservation practices within the basin was predicted to have reduced nutrient loads to the Gulf by 20%. The results also indicate the importance of targeted implementation of conservation practices. The present application illustrates the value of the Cropland CEAP modeling framework as a powerful, science-based tool to evaluate agricultural conservation approaches.

Technical Abstract: Excessive nutrients transported from the Mississippi River Basin have created an ecological disaster - Gulf of Mexico hypoxia. Also, in recent years, federal expenditures on agricultural conservation practices have received intense scrutiny. Partly driven by these factors, the USDA Conservation Effects Assessment Project (CEAP) recently completed a comprehensive evaluation of nutrient sources and delivery to the Gulf. The modeling framework used in the CEAP Cropland National Assessment or “Cropland CEAP” consists of the Agricultural Policy/Environmental eXtender (APEX) and Soil and Water Assessment Tool (SWAT) models. This modeling framework was successfully calibrated and was rigorously validated. Results indicated that overall cultivated cropland is the dominant source of N and P to both local waters and the Gulf, but this was not true for each water resource region within the Basin. In addition, the results showed that point sources remain significant contributors of P loads, especially in the Tennessee and Arkansas/Red River Basins where point source P loads exceed those from cultivated cropland. Similarly, urban nonpoint sources are significant N and P sources. The Upper Mississippi, Lower Mississippi, and Ohio Basins are the dominant sources of nutrients delivered to the Gulf. The high delivery areas near the Mississippi River main stem, from which 87% of N and 90% of P reaches the Gulf, coincides with elevated nutrient yields to local waters. The establishment of conservation practices within the basin was predicted to have reduced nutrient loads to the Gulf by 20% based on this CEAP study. The results indicate the importance of targeted implementation of conservation practices and consideration of local water and/or Gulf impacts depending on program goal(s). The present application illustrates the value of the Cropland CEAP modeling framework as a powerful, science-based tool to evaluate pollutant sources and delivery and effects of agricultural conservation approaches.