Distribution of average nitrogen yields at 65 stream sites in the Chesapeake Bay watershed for the period 2007-2011 was spatially variable but there were some general patterns in location.
Yields are tons of nitrogen per square mile of land that drains to each monitoring site.
To view an interactive version of the map featured below, go to http://cbrim.er.usgs.gov/maps/index.html.
Date created: Jan 02 2013 / Download
Average yields for total nitrogen (TN) were estimated for the last five years at 65 sites and classified into thirds as high, medium, and low. While the distribution was spatially variable, there were some general patterns in location. Generally, higher yields for TN are dominant in the middle of the watershed, areas that also coincide with large urban and agricultural land uses. The lowest yields are generally in the Virginia watersheds.
Data (136.5 KB) Nitrogen is a type of nutrient contributing to poor water quality in aquatic ecosystems. Elevated nitrogen levels may cause excessive algal growth, blocking out sunlight and reducing oxygen for fish and other underwater life.
Nitrogen concentrations are monitored near the head of tide (River Input Monitoring Program) in nine of the Bay's major tributaries, and at 56 locations upstream from the River Input sites.
Yields
Average yields for nitrogen were estimated for the last five years at 65 sites and classified into thirds as high, medium, and low. While the distribution was spatially variable, there were some general patterns in location.
In the map, yields are color coded: high (orange), medium (yellow), and low (blue).
Yields delivered to Chesapeake Bay may differ from values portrayed in this indicator due to downstream ecological processes. For more information on nitrogen yields delivered to the Bay see Nitrogen Loads and River Flow to the Bay.
Additional Information
The short-term yields 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. and 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/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 65 of these sites have enough of a long-term record to calculate nutrient and sediment yields.
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 and yields. 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
