USGS: Mississippi River Nitrate Levels Continue to Increase; Signs of Progress in the Illinois River

USGS Long-term Nitrate Trends
Monitoring Sites

On October 30, the U.S. Geological Survey (USGS) reported that Illinois River nitrate levels decreased by 21 percent between 2000 and 2010, based on long-term River water quality observations at Valley City, Illinois.  Those results marked the first time that substantial, multi-year decreases in nitrate were observed in the Mississippi River Basin since 1980, according to a new National Water-Quality Assessment (NAWQA) Program study. NAWQA evaluated nitrate concentrations and flux from 1980 through 2010 at eight sites in the Mississippi River Basin as part of the study. Nitrate decreases were also noted in the Iowa River during the same time period; although the decline was not as large (10 percent).  Similar declines were not widespread in the water basin, however, according to Lori Sprague, USGS research hydrologist and a study author, who noted, "Nitrate levels continue to increase in the Missouri and Mississippi Rivers, including the Mississippi’s outlet to the Gulf of Mexico." The study results between 2000 and 2010 demonstrated consistent increases in nitrate concentrations in the upper Mississippi River (29 percent) and the Missouri River (43 percent), while nitrate concentrations at the Mississippi River outlet to the Gulf of Mexico increased by 12 percent. Excessive nitrate and other nutrients from the Mississippi River are major factors contributing to the extent of the hypoxic zone (or "dead zone") that forms in the northern Gulf of Mexico every summer. Additional details and a link to the report can be found at this USGS study web site: "Nitrate in the Mississippi River and Its Tributaries, 1980–2010: An Update."