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Water Quality Loads and Trends at Nontidal Monitoring Stations in the Chesapeake Bay Watershed

Summary of Trends and Yields Measured at the Chesapeake Bay Nontidal Network Sites: Water Year 2012 Update

Prepared by the U.S. Geological Survey, November 25, 2013

The U.S. Geological Survey (USGS), works with partners in the Chesapeake Bay Program (CBP) to operate the Nontidal water-quality monitoring network. This network is designed to measure changes in nutrients and sediment in the Chesapeake Bay watershed. The nutrient and sediment data are updated and interpreted each year. The update of 2012 information includes:

  • Long-term trends in concentrations (1985-2012)
  • Short-term trends in concentrations (2003-2012)
  • Yields as an indicator of the relative loads among watersheds (2008-2012)

Because the goals of Bay restoration efforts are to reduce nitrogen, phosphorus and sediment reaching the Bay, downward trends in concentration are considered improving conditions, while increasing trends are considered degrading conditions. The major findings for nutrient and sediment concentration trends and yields in the Chesapeake Bay watershed through 2012 are:

  • Across the watershed, about 70 percent of the sites are showing long-term improvements in nitrogen and phosphorus. Over the past 10 years, nitrogen conditions have improved at about one half of the sites, while phosphorus concentrations show little or no change at more than one half of sites.

  • The amount of improvement for sediment concentrations is smaller than the nutrients with 28 percent showing an improvement over the long-term and 10 percent showing improvements over the last decade. Just under half of the sites show little change over the long term or past decade. However, 41 percent show degrading flow-adjusted sediment concentrations over the past 10 years.

  • Nitrogen, phosphorus and sediment yields at Chesapeake monitoring sites are highly variable. High yielding sites for nutrients are located in portions of the Susquehanna, Potomac and Rappahannock watersheds as well as the Eastern Shore. The lowest sediment yielding sites are located on the Eastern Shore and the York River Basin.


The following text describes the most recent results for nitrogen, phosphorus and sediment trends and yields. Table 1 provides a summary of flow adjusted trend results for the network.

Nitrogen

  • Long Term Trend: Seventy percent of long-term stream monitoring sites in the Chesapeake Bay Watershed have improving flow-adjusted concentrations of nitrogen. Between 1985 and 2012:
    • 21 out of 30 sites show improving flow-adjusted trends for nitrogen concentrations,
    • 3 sites show degrading trends, and
    • 6 sites show small changes that are not statistically significant.

  • Short Term Trend: Over the past 10 years, 54 percent of the monitoring stations show improving flow-adjusted nitrogen concentrations. Only one site showed degrading nitrogen conditions. Between 2003 and 2012:
    • 25 out of 46 sites show improving flow-adjusted trends for nitrogen concentrations,
    • 1 site shows degrading trends, and
    • 20 sites show small changes that are not statistically significant.

  • Watershed Yield: Total Nitrogen yields ranged from 0.33 to 9.87 tons per square mile. Each of the 17 sites in the high yield category carries more than 3.4 tons of nitrogen per square mile of watershed. These sites are generally located on the Eastern Shore, Lower Susquehanna and Northern Potomac Watersheds. The lowest yields, which are less than 1.2 tons per square mile, are generally in the Upper Potomac and Southern Virginia Rivers.

Phosphorus

  • Long Term Trend: Seventy-three percent of long-term stream monitoring sites in the Chesapeake Bay Watershed show improving flow-adjusted concentrations of phosphorus. Between 1985 and 2012:
    • 22 out of 30 sites show improving flow-adjusted trends for phosphorus concentrations,
    • 4 sites show degrading trends, and
    • 4 sites show small changes that are not statistically significant.

  • Short Term Trend: Over the past 10 years, 63 percent of the monitoring stations show little or no change in flow-adjusted phosphorus concentrations. Between 2003 and 2012:
    • 9 out of 43 sites show improving flow-adjusted trends for phosphorus concentrations,
    • 7 site shows degrading trends, and
    • 27 sites show small changes that are not statistically significant.

  • Watershed Yield: Total Phosphorus yields ranged from 0.036 to 0.57 tons per square mile. Each of the 17 sites in the high yield category carries more than 0.19 tons of phosphorus per square mile of watershed. High yielding sites were found in the Eastern Shore, Susquehanna, Potomac, and Rappahannock Watersheds. The lowest yields are generally in the western areas of the Bay watershed and the York River Basin.

Sediment

  • Long Term Trend: Forty-four percent of long-term stream monitoring sites in the Chesapeake Bay Watershed show little change in flow-adjusted concentrations of sediment. The remaining sites were evenly split between improving and degrading conditions. Between 1985 and 2012:
    • 8 out of 29 sites show improving flow-adjusted trends for sediment concentrations,
    • 8 sites show degrading trends, and
    • 13 sites show small changes that are not statistically significant.

  • Short Term Trend: Over the past 10 years, 49 percent of sites show little change while 41 percent show degrading flow-adjusted sediment concentrations. Between 2003 and 2012:
    • 4 out of 39 sites show improving flow-adjusted trends for sediment concentrations,
    • 16 site shows degrading trends, and
    • 19 sites show small changes that are not statistically significant.

  • Watershed Yield: Sediment yields ranged from 9.3 to 648 tons per square mile. Each of the 17 sites in the high yield category carries more than 200 tons of sediment per square mile of watershed. High yielding sites are spatially dispersed across the Susquehanna, Potomac and Rappahannock watersheds. The lowest sediment yielding sits are located on the Eastern Shore and the York River Basin.

Table 1. Summary of long-term and short-term trends in flow-adjusted concentration for stations in the Chesapeake Bay Nontidal Network.

trends and yields summary table1

Additional Information:

  • Maps of the flow-adjusted concentration results are available as:
  • Tabular results for each station are available in the "Download" section of the navigation menu on this web site.
  • A summary of loads at the river-input stations is also on the 2012 Loads Summary Page.
The USGS also developed a new technique to compute flow-normalized loads. Results from this technique are planned in future updates. For more information go to: http://chesapeake.usgs.gov/sciencesummary-enhancedstatistical.html

Contacts:

Joel Blomquist, Baltimore MD,
Doug Moyer, Richmond, VA,
Ken Hyer, Richmond, VA,
Mike Langland, New Cumberland, PA,

For more information on USGS Chesapeake Bay Studies, contact Scott Phillips, or visit http://chesapeake.usgs.gov/


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