Long-term monitoring of nitrate levels in 22 large rivers shows no widespread evidence of improvement, although nitrogen from fertilizer and livestock sources has been fairly stable since the 1980s, says the U.S. Geological Survey. Nitrate levels increased as much as five-fold in river water in intensively farmed sections of the Midwest from 1945-80. Since then, “nitrate changes have been smaller as the increase in fertilizer use has slowed in the Midwest and large amounts of farmland have been converted to forest or urban land along the East coast,” says USGS. Edward Stets, the lead author of a USGS study on nitrate levels, says, “Although the greatest increases in nitrate concentrations occurred prior to 1980, levels have since remained high in most rivers.”