The NAWQA trends assessment for nutrients in streams reflects periodic measurements of concentrations of nitrogen and phosphorus from 1993 to 2003 (yellow vertical shaded area). Dubrovsky, N.M., and Hamilton, P.A., 2010, USGS

The NAWQA trends assessment for nutrients in streams reflects periodic measurements of concentrations of nitrogen and phosphorus from 1993 to 2003 (yellow vertical shaded area). This was a period of relatively small changes in nitrogen fertilizer use, which followed a more than 10-fold increase in fertilizer use between about 1950 and the early 1980s. There also has been a more than three-fold increase in population in the Nation since 1900. These increases in nitrogen sources are reflected in the large increases in concentrations of nitrate in streams as disparate as the Blackstone River in urbanized Massachusetts and the San Joaquin River in the agricultural Central Valley of California. Dubrovsky, N.M., and Hamilton, P.A., 2010, Nutrients in the Nation’s streams and groundwater: National Findings and Implications: U.S. Geological Survey Fact Sheet 2010-3078, 6 p. [pdf]

Elevated Nitrogen and Phosphorus Still Widespread in Much of the Nation’s Streams and Groundwater