While the Bay region has seen a long-term decline in nutrients in many areas since 1985, those trends have leveled off in recent years — and improvements for phosphorus have largely halted — according to recent water quality monitoring data.

The data, released by the U.S. Geological Survey, largely confirm findings in other recent reports which have generally shown a decline in nitrogen and phosphorus concentrations in many rivers since 1985, but less improvement during the most recent 10 years.

In fact, the new data — which includes monitoring results through 2013 — detected no significant improving phosphorus trends in any of the nine largest Bay tributaries during the previous 10 years, while phosphorus concentrations showed significant increasing trends in two: the Susquehanna and the Choptank rivers.

On a more positive note, the data show significant long-term and short-term downward trends in nitrogen concentrations in the Bay’s two largest tributaries, the Susquehanna and the Potomac, as well as in the Patuxent. Still, while five rivers had long-term decreasing trends for nitrogen, only three maintained those trends through the most recent decade.

The data is collected from nine river input monitoring sites located just above the tidal zone of major Bay tributaries — usually near the fall line, which divides the Coastal Plain from the Piedment.

River water originating from about 78 percent of the Bay’s 64,000-square-mile watershed flows past those sites, and the upstream region is the source of about 60 percent of the nutrients reaching the Chesapeake.

The monitoring sites tend to be located upstream of many of the region’s largest wastewater treatment plants, and therefore do not capture most of the significant reductions achieved by upgrading those facilities in recent decades.

The data do not attempt to explain the factors affecting water quality trends, though the continued short-term nitrogen reductions in the two largest watersheds — the Potomac and Susquehanna — likely benefited from substantial reductions in air pollution which have taken place since 2000. Both watersheds are downwind of major power plants that have been required to significantly reduce nitrogen oxide emissions, and recent research has shown nitrogen reductions in streams which appear linked to those improvements.

The USGS and other Bay Program agencies are planning a series of reports that will attempt to examine actions that are impacting those trends over time.

For individual rivers, the data shows:

Susquehanna (at Conowingo, MD)

  • Nitrogen: Decreasing long– (1985-2013) and short-term (2003-2013) trends
  • Phosphorus: No long-term trend, increasing short-term trend
  • Sediment: No significant long– or short-term trend

Potomac (at Washington, DC)

  • Nitrogen: Decreasing long– and short-term trends
  • Phosphorus: Decreasing long-term trend, no significant short-term trend
  • Sediment: Decreasing long-term trend, no short-term trend

James (at Cartersville, VA)

  • Nitrogen: Decreasing long-term trend, no significant short-term trend
  • Phosphorus: Decreasing long-term trend, no significant short-term trend
  • Sediment: No significant long– or short-term trend

Rappahannock (at Fredericksburg, VA)

  • Nitrogen: Decreasing long-term trend, no significant short-term trend
  • Phosphorus: No significant long– or short-term trend
  • Sediment: No significant long– or short-term trend

Appomattox (at Matoaca, VA)

  • Nitrogen: No significant long– or short-term trends
  • Phosphorus: Increasing long-term trend, no significant short-term trend
  • Sediment: No significant long-term trend, increasing short-term trend


Pamunkey (at Hanover, VA)

  • Nitrogen: Increasing long-term trend, no significant short-term trend
  • Phosphorus: Increasing long-term trend, no significant short-term trend
  • Sediment: Increasing long-term and short-term trend

Mattaponi (near Beulahville, VA)

  • Nitrogen: No significant long– or short-term trend
  • Phosphorus: No significant long– or short-term trend
  • Sediment: No significant long– or short-term trend

Patuxent (at Bowie, MD)

  • Nitrogen: Decreasing long– and short-term trend
  • Phosphorus: Decreasing long-term trend, no significant short-term trend
  • Sediment: Decreasing long-term trend, increasing short-term trend

Choptank (near Greensboro, MD)

  • Nitrogen: Increasing long– and short-term trend
  • Phosphorus: Increasing long– and short-term trend
  • Sediment: Decreasing long-term trend, increasing short-term trend

The USGS also reported that during its most recent year of data— 2013 — the nutrients flowing past the nine monitoring sites and into Bay tidal waters were below the long-term average.

Nitrogen loads reaching tidal waters in 2013 were about 160 million pounds, below the long-term average of 212 million.

Phosohorus loads were 10 million pounds, compared with the long-term average of 14.6 million pounds.

Sediment loads were 2.7 million tons which is less than the long-term average of 5.2 million tons.

Those figures do not include estimates of nutrients entering the Bay from below monitoring sites, which covers 22 percent of the watershed.

For information, visit the USGS Chesapeake Bay Activities webpage