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Understanding nitrate delivery within the Big Sunflower River, Mississippi: implications for nutrient loads to the Gulf of Mexico

Robert Kröger

Graduate Student(s):  Jeannie Barlow

This project is a collaborative project between USGS, USACE and MSU. This project was funded through a collaborative agreement through USGS and USACE in July 2010, and is expected to be completed by August, 2013.

The overall objective of this study is to determine the relative roles of in-stream processing and groundwater/surface-water exchange on the transport and fate of nitrate in the Big Sunflower River and how these roles change in response to groundwater-levels in the alluvial aquifer. The Big Sunflower River Basin, located within the Yazoo River Basin, is susceptible to large annual inputs of N from agriculture, atmospheric deposition, and point sources. Recent publications imply that N, once it enters the surface waters of the Big Sunflower River Basin, acts conservatively and does not undergo significant denitrification. The management implication is that if one molecule of N can be prevented from reaching a stream in the Yazoo River Basin, then that is one less molecule of N reaching the Gulf of Mexico and contributing to the seasonal occurrence of hypoxia. The denitrification rates suggested are calculated from all available data, which unfortunately does not include any studies from the flat, humid, and semi-tropical Yazoo River Basin. The major variables that affect denitrification rates in streams (other than the concentration of dissolved oxygen) are temperature, stream velocity, and the exchange of surface water with the benthic zone of the streambed, which is influenced by the rate and direction of groundwater/surface-water exchange. View and explore Real-time data from this project here: ms.water.usgs.gov.


  • Barlow, J.R.B., B.R. Clark. 2011, Simulation of water-use conservation scenarios for the Mississippi Delta using an existing regional groundwater flow model: U.S. Geological Survey Scientific Investigations Report 20115019, 14 p.
  • Barlow, J.R.B., R.H. Coupe. 2011, Groundwater and surface-water exchange and resulting nitrate dynamics in the Bogue Phalia Basin in northwestern Mississippi, Journal of Environmental Quality, in press.

Gulf of Mexico Research

Completed Projects