The following information was reproduced from an email notification provided by Dr. William Wilber, USGS.
"New USGS Study—U.S. Rivers Show Few Signs of Improvement from Historic Nitrate Increases
A recent U.S. Geological Survey (USGS) (http://onlinelibrary.wiley.com/doi/10.1111/1752-1688.12321/full) provides a rare glimpse into how nitrate levels in 22 large rivers across the Nation have changed over the last 65 years.
During 1945 to 1980, nitrate levels in large U.S. rivers increased up to fivefold in intensively managed agricultural areas of the Midwest. In recent decades, nitrate changes have been smaller and levels have remained high in most of the rivers studied.
The greatest increases in river nitrate levels coincided with increased nitrogen inputs from livestock and agricultural fertilizer, which grew rapidly from 1945 to 1980. In some urbanized areas along the East and West coasts during the same period, river nitrate levels doubled. Since 1980, 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.
The USGS study, reported in the Journal of the American Water Resources Association, includes rivers flowing into the Great Lakes and coastal waters such as Long Island Sound, Delaware River estuary, Chesapeake Bay, San Francisco Bay, and the Gulf of Mexico.
Track water quality online (http://cida.usgs.gov/quality/rivers/home) at 108 streams and rivers monitored as part of the USGS National Water-Quality Assessment project.
For additional information on the long-term nitrate study, contact Ted Stets, estets@usgs.gov."