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USGS Finds Nitrate Levels Show No Consistent Decline in the Mississippi River Basin

Despite efforts to reduce nitrate in the Mississippi River basin, nitrate concentrations and transport at eight main stem or large tributary sites have not declined from 1980-2008. The results are based on a new statistical method developed by the U.S. Geological Survey that takes into account variation in river flows, in order to paint an accurate picture of long term trends.  These results reflect the cumulative changes over time in nitrate sources and conservation practices throughout the Mississippi River basin, and highlight the need for comprehensive nutrient management strategies that will reduce nutrients in both streams and groundwater.

Key findings:

  • Nitrate concentrations increased considerably at two sites (Mississippi River at Clinton, IA and at Missouri River at Hermann, MO).
  • Nitrate concentrations remained very nearly the same or increased at the other six sites (Iowa River at Wapello, IA; Illinois River at Valley City, IL; Ohio River near Grand Chain, IL; and along the Mississippi River at Grafton, IL; at Thebes, IL; and near the Old River Outflow Channel).
  • Nitrate transport to the Gulf of Mexico increased from 1980 to 2008.
  • Increases in nitrate concentrations in groundwater are having a substantial effect on nitrate concentrations in rivers and transport to the Gulf of Mexico.  The evidence for this comes from the fact that increases in nitrate concentrations are particularly large during low flow conditions.

For more information and to view the study findings, visit the journal of Environmental Science & Technology web site at: http://water.usgs.gov/nawqa/pubs/nitrate_trends/ or contact Lori Sprague of USGS at lsprague@usgs.gov or 303-236-6921.  For more information about the NAWQA program, visit the USGS web site at: http://water.usgs.gov/nawqa/.