Special thanks to Susan Heathcote with Iowa Environmental Council for this Summary.
An interesting report was released yesterday by the US Geological Survey about the long-term trends in nitrate levels in the Mississippi River and major tributaries. The study looked at nitrate trends over the period 2000 – 2010.
Overall nitrate concentrations increased 12% at the outlet of the Mississippi River into the Gulf of Mexico. There is some good news and bad news here. The nitrate concentration trends show a decrease in both the Illinois River (21%) and Iowa River (10%). These decreases were offset by large increases in the upper Mississippi above Clinton, Iowa (29%) and the Missouri River (43%). The nitrate concentrations in the Ohio River are the lowest of the major tributaries and have remained relatively constant over the past 30 years.
Also interesting is that USGS found that nitrate increased at low stream flows throughout the basin, except for the Ohio and Illinois Rivers. The report suggests that increases during low flow are likely dominated by point sources from wastewater treatment plants and groundwater recharge of legacy nitrate from past practices on the land that may take years to move through the subsurface to the Mississippi River. Because of the lag time for groundwater recharge, it might take many years to see water quality improvements in the Mississippi River and Gulf.
See press release http://www.usgs.gov/newsroom/article.asp?ID=3715#.UnKBqZko4cA
The full report is available online at http://pubs.usgs.gov/sir/2013/5169/