The majority of long-term stream monitoring sites show trends indicating decreasing flow-adjusted concentrations of nitrogen. Decreasing flow-adjusted concentrations of this pollutant suggest that conditions in rivers and streams have been improving since the mid 1980s.
Between 1985 and 2011:
At many monitored locations, long-term trends indicate that management actions, such as pollution controls for improved wastewater treatment plants and practices to reduce nutrients on farms and suburban lands have reduced concentrations of nitrogen. While these reductions provide evidence of improving conditions in some upstream areas, additional reductions will be needed to have healthier streams and meet water-quality goals for the Bay.
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Date created: Jan 02 2013 / Download
Changes in nitrogen concentrations have been determined for the period 1985-2011 at 31 stream sites in the Chesapeake Bay watershed. Of these, the majority of the flow-adjusted trends were improving, with 21 sites having improving trends, 3 sites had degrading trends, and 7 sites the trends were not statistically significant.
Nitrogen concentrations are highly variable, depending on the amount of water flowing in streams and rivers throughout the Bay watershed. Therefore, scientists calculate flow-adjusted trends to determine whether concentrations have changed over time. By removing the effects of natural variations in streamflow, resource managers can evaluate the changes in stream health that may result from nutrient-reduction actions or other changes within the watershed.
Since the 1980s, Bay Program partners have collected data on stream flow and water quality at 31 locations throughout the non-tidal portions of the watershed. These watershed monitoring sites collectively represent 78 percent of the area of the Bay basin and range in size from the 100-square-mile Choptank River watershed to the Susquehanna River’s 27,000 square mile watershed.
The goal is to observe downward trends in flow-adjusted nitrogen concentrations at monitoring sites across the Bay watershed.
The flow-adjusted trends indicator is calculated and published annually by the U.S. Geological Survey as part of a larger effort to determine loads and trends in nutrient and sediment concentrations and streamflow in the Chesapeake Bay watershed. A complete description of data analysis methods can be found in Langland, M. J., and others, Changes in streamflow and water quality in selected nontidal basins in the Chesapeake Bay watershed, 1985-2004: U.S. Geological Survey Scientific Investigations Report 2006-5178, 75 p. Even more information related to the methods of data analysis and current results are available at: http://cbrim.er.usgs.gov/
The Chesapeake Bay Program (CBP), in partnership with USGS and agencies in six states throughout the Chesapeake Bay watershed, monitors streamflow, nutrients and sediment as part of the CBP Nontidal Water Quality Monitoring Network. There are 85 sites in the network; however, only 31 of these sites have enough of a long-term record to calculate flow-adjusted concentration trends.
The network includes the River Input Monitoring Program, which monitors streamflow and water quality at nine sites upstream from the head of tide at each of the major river basins draining to the Bay. The River Input sites collectively represent 78 percent of area of the watershed and range in size from the Susquehanna River (27,000 square miles) to the Choptank River (100 square miles). These nine rivers account for approximately 93 percent of the streamflow entering Chesapeake Bay from the nontidal part of its watershed. However, many of the largest populated cities within the watershed are located downstream of these monitoring sites in the Coastal Plain region of the watershed.
Results from the CBP Nontidal Water Quality Monitoring Network are being used by resource managers, policy makers and concerned citizens to help evaluate the effectiveness of strategies aimed at reducing nutrients and sediment entering streams and rivers of the Chesapeake Bay watershed and, eventually, the tidal waters of the Bay.
Most of the monitoring is conducted upstream from the head of tide. Thus, the trends do not reflect the effects of management actions that are implemented in the majority of the Coastal Plain areas of the watershed.
There are multiple factors affecting nutrient trends. The major factors include changes in nutrient sources and land use, population increase, implementation of management actions, and the influence of watershed characteristics including the lag time between implementing management actions to decrease nutrient pollution and detecting a water quality improvement.
Scott Phillips
USGS Chesapeake Bay
(443) 498-5552
US Geological Survey
