Maps

Long-term trends were computed by state partners using the Seasonal Kendall non-parametric technique for annual data collected from 1999-2013. Highly significant trends are indicated with triangles and possible trends are show with colored circles. Bottom total nitrogen concentrations are decreasing/improving significantly at 31 stations, possibly decreasing at 15 stations, and increasing/degrading significantly at 1 station.

Long-term trends were computed by state partners using the Seasonal Kendall non-parametric technique for annual data collected from 1999-2013. Highly significant trends are indicated with triangles and possible trends are show with colored circles. Surface total nitrogen concentrations are decreasing/improving significantly at 41 stations, possibly decreasing at 16 stations, increasing/degrading significantly at 1 station, and possibly increasing at 1 station.

Over the past decade, one-third of the monitoring sites in the Chesapeake Bay watershed have shown improving flow-adjusted trends in nitrogen concentrations. Between 2004 and 2013: three out of nine sites—including the Patuxent, Potomac and Susquehanna rivers—have shown improving trends for nitrogen concentrations. One site—the Choptank River—has shown degrading trends. Five sites—including the Appomattox, James, Mattaponi, Rappahannock and Pamunkey rivers—have shown minor changes that are not statistically significant.

Fifty-five percent of monitoring sites in the Chesapeake Bay watershed show improving long-term flow-adjusted trends in nitrogen concentrations. Between 1985 and 2013: five out of nine sites—including the James, Patuxent, Potomac, Rappahannock and Susquehanna rivers—have shown improving trends for nitrogen concentrations. Two sites—including the Choptank and Pamunkey rivers—have shown degrading trends. Two sites—including the Appomattox and Mattaponi rivers—have shown minor 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.

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.

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.

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.

Over the past 10 years, the majority of nitrogen concentration trends are non-significant (28 sites), with 19 sites showing improving condition and only 1 site showing degrading conditions. The trend results indicate that in many locations, management actions, such as improved wastewater treatment and nonpoint-source pollution controls (i.e. urban stormwater runoff and agricultural runoff controls), have reduced nitrogen concentrations in streams.

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.