Nutrient pollution in the majority of the Chesapeake Bay region’s freshwater streams and rivers has decreased over the last 25 years, according to data from scientists with the U.S. Geological Survey (USGS) and the Chesapeake Bay Program.
Almost 70 percent of the watershed’s 32 monitoring locations show decreasing nitrogen and phosphorus levels, meaning fewer of these harmful nutrients are entering the Chesapeake’s local waterways. Approximately 40 percent of the sites show decreasing trends for sediment pollution.
Although this data may indicate long-term improvements in the health of the Bay’s streams and rivers, pollution loads to the Bay were higher in 2010 due to more rain, snow and river flow.
“These long-term trends indicate that pollution reduction efforts, such as improved controls at wastewater treatment plants and practices to reduce nutrients and sediment on farms and suburban lands, are improving water quality conditions in many areas,” said USGS scientist Scott Phillips. “However, nutrients, sediment and contaminants will need to be further reduced to achieve a healthier Bay and streams.”
Each day, billions of gallons of fresh water flow through thousands of streams and rivers that eventually empty into the Bay. This fresh water is known as “river flow.” In general, as river flow increases, more nutrient and sediment pollution is carried downstream to the Bay. Pollution levels in rivers vary greatly from year to year because they are influenced by rainfall. Scientists make adjustments to remove the effects of weather variations, allowing consistent measurement of pollution levels over time and better evaluation of long-term changes.
In the 2010 water year (October 2009-September 2010):
The Bay Program’s goal is to have a long-term average of 186 million pounds of nitrogen and 12.5 million pounds of phosphorus entering the Bay from streams and rivers.
In a different, shorter-term study conducted between 2000 and 2008, the health of individual freshwater streams across the watershed showed mixed conditions. Of the 7,886 stream sites sampled, more than half (55 percent) were found to be in very poor or poor condition. The remaining 45 percent were found to be in fair, good or excellent condition.
This study uses data on the tiny, bottom-dwelling creatures that live in freshwater streams and rivers as an indicator of overall stream health. This method provides a uniform evaluation of the health of local waterways across state lines and throughout the entire Bay watershed.
The USGS estimates how much river flow enters the Bay each year, monitors pollution loads in the Bay’s major rivers, and works with the Bay Program to estimate how much pollution reaches the Bay. To learn more about the USGS’s Chesapeake monitoring activities, visit http://chesapeake.usgs.gov.