A newly published study by the U.S. Geological Survey scientists finds that, from 2002 to 2012, decreases in loads of nitrogen compounds, including nitrate, were more common than decreases in loads of phosphorus compounds in the studied water bodies.
U.S. Geological Survey scientists have been tracking trends in nutrient loads entering the nation’s coastal waters and estuaries, including San Francisco Bay and Chesapeake Bay, and the Great Lakes.
Excessive amounts of nutrients (a phenomenon known as eutrophication), mostly nitrogen and phosphorus, are one of the main causes of algal blooms and resulting fish kills.
Most of the decreases in nitrogen loading were in urban watersheds and could reflect regulatory actions to reduce nutrient loading from point sources such as wastewater treatment plants. There was a less consistent pattern of trends in loading from agricultural areas, where nonpoint source loading of nutrients—more difficult to control than point source loading—is more common. Loading of total nitrogen and total phosphorus to coastal waters from streams with little development in their watershed increased from 2002 to 2012, indicating that water quality in these coastal watersheds is degrading despite minimal human activity.
Also, of note, the ratio of total nitrogen to total phosphorus—the N-to-P ratio—was higher than pre-1979 levels.
For additional information on the study, contact Gretchen Oelsner, goelsner@usgs.gov.
Click here to view a USGS interactive map on trends in water quality of the nation’s streams and rivers.
