The Fate and Transport of Nitrate in the Surface Waters of the Big Sunflower River in Northwest Mississippi

Author(s): Wood, M.; Coupe, R.

The Mississippi Alluvial Plain, an area lying within the Yazoo River basin in northwestern Mississippi, locally referred to as the Delta, is a relatively flat landscape where approximately 90 percent of the land is used for cultivation of corn, cotton, rice, soybeans, and catfish. Annually, the Yazoo River basin contributes around 1–3% of the nitrogen load to the Gulf of Mexico. Recent modeling studies suggest that that there is very little processing of nitrogen in the main channel and primary tributaries of the Yazoo River basin; nitrogen acts conservatively and does not undergo significant reduction through processes such as denitrification. The nitrogen loss rates used in these models are from other areas as there have been few studies on denitrification rates in the Delta. The Delta, which differs from the topography and climate of most of the rest of the United States, has slower stream velocities and higher temperatures than many areas of the United States; two key variables that control denitrification rates. If there is significant processing of nitrogen in the streams of the Yazoo River basin, this could have implications for managing nutrient reduction in streams and rivers of the Delta. During April–August 2010, four sets of samples were collected at ten sites located on the Big Sunflower River. Samples were analyzed for nitrate, nitrite, organic nitrogen, total nitrogen, chloride and sulfate. A Lagrangian procedure that followed the same parcel of water as it transited the Big Sunflower River was used to time the collection of the water samples. The objective of the study is to determine if nitrogen, once in the Big Sunflower River, is conservative in nature or undergoes significant loss.

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