Short-term changes in Sediment concentrations have been determined for the period 2002-2011 at 41 stream sites in the Chesapeake Bay watershed:
Improving trends in flow-adjusted concentrations indicate improvements in water quality conditions. Degrading trends may be used to identify watersheds that may require an increased level of pollution control.
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Date created: Jan 02 2013 / Download
Over the past 10 years, the majority of sediment concentration trends are non-significant monitoring at sites within the Bay watershed with many sites showing degrading condition and only a few are improving. The trend results indicate that at some monitored locations, short-term trends indicate that management actions, such as efforts to curb erosion and runoff have reduced concentrations of sediment. 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.
Suspended sediment consists of the fine and medium-grained particulate matter that is transported in streams and rivers. Excess sediment in stream channels, causes impaired benthic habitat and decreased water clarity. When delivered to the Chesapeake Bay, suspended sediment causes impaired aquatic habitat, reduced water clarity, and can fill in navigational channels and embayments.
Sediment concentrations are highly variable and strongly related to streamflow conditions. Flow-adjusted trends are calculated in order to statistically determine whether concentrations have changed over time by removing the effects of natural variations in streamflow. Because flow-adjusted trends are independent of streamflow variations, they permit evaluation of the changes in sediment concentration that may result from erosion and runoff controls or other changes within the watershed.
Sediment concentrations are monitored near the head of tide (River Input Monitoring Program) in nine of the Bay's major tributaries, and at 32 locations upstream from the River Input sites.
Stream quality is associated with lower nutrient concentrations and loads; therefore, the goal for short-term flow-adjusted concentration trends is to observe the majority of the sites as having improving trends in flow-adjusted sediment concentrations and few sites as degrading.
Short-term trend (2002-2011)
Over the past 10 years, the majority of sediment concentration trends are non-significant monitoring at sites within the Bay watershed with many sites showing degrading condition and only a few are improving. The trend results indicate that at some monitored locations, short-term trends indicate that management actions, such as efforts to curb erosion and runoff have reduced concentrations of sediment. 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.
In the map, arrows with different directions (up or down) are portrayed to present this information; no significant change is indicated by a black dot.
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.; additionally refer to: Langland, Michael, Blomquist, Joel, Moyer, Douglas, and Hyer, Kenneth, 2012, Nutrient and suspended-sediment trends, loads, and yields and development of an indicator of streamwater quality at nontidal sites in the Chesapeake Bay watershed, 1985–2010: U.S. Geological Survey Scientific Investigations Report 2012–5093, 26 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 over 120 sites in the network; however, only 41 of these sites have enough of a short-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 sediment trends and yields. The major factors include changes in sediment 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 sediment pollution and detecting a water quality improvement.
Scott Phillips
USGS Chesapeake Bay
(443) 498-5552
US Geological Survey
