A U.S. Geological Survey (USGS) on Oct. 30 released a new study showing nitrate levels in the Illinois River have decreased 21% between 2000 and 2010. The Mississippi River Basin has not seen a multi-year decrease in levels since 1980.
While the Illinois River has exhibit a decrease in nitrate levels, the Missouri and Mississippi River has not showed similar signs of progress according to USGS.
"Nitrate levels continue to increase in the Missouri and Mississippi Rivers, including the Mississippi’s outlet to the Gulf of Mexico," said Lori Sprague, USGS research hydrologist.
The reasons for increases or declines in annual nitrate levels are unknown. Reliable information on trends in contributing factors, such as fertilizer use, livestock waste, agricultural management practices, and wastewater treatment improvements, is needed to better understand what is causing increases or decreases in nitrate.
Key nitrate concentration trend findings at long-term USGS monitoring sites:
Nitrate concentrations steadily decreased by 21 percent in the Illinois River from 2000 to 2010. Decreases were also noted in the Iowa River during this time, but the declines were not as large (10 percent).
Consistent increases in nitrate concentrations occurred between 2000 and 2010 in the upper Mississippi River (29 percent) and the Missouri River (43 percent).
Nitrate concentrations in the Ohio River are the lowest among the eight Mississippi River Basin sites and have remained relatively stable over the last 30 years.
Nitrate concentrations increased at the Mississippi River outlet by 12 percent between 2000 and 2010.
The USGS report and additional information is available at http://water.usgs.gov/nawqa/pubs/nitrate_trends/ .