Nitrate levels in two key Mid­western rivers, the Iowa and the Illinois, declined in the decade from 2000 to 2010 according to new report by the U.S. Geological (USGS) survey. However, the report showed mixed results on nitrate levels at other monitoring sites in the Mississippi River basin, with higher levels showing up in the Mississippi and Missouri rivers and at the Gulf of Mexico.

The results of the study show that farmers’ efforts to conserve soil and reduce nutrient loss can help to improve surface water...