Chesapeake Bay Benthic Monitoring Program

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Summary of Results

The area of the Chesapeake Bay estimated to fail the Benthic Community Restoration Goals in 2017 was 4,752 416 km2, or 41% of the tidal bottom (Figure 1). For the Maryland portion of the Bay, the area was 3,333 305 km2, or 53% of the tidal bottom. These estimates indicate an improvement in benthic condition between 2016 and 2017, primarily in Maryland tidal waters. Over the 1995-2017 time series, there were no statistically significant changes in percent degraded area in Chesapeake Bay or Maryland tidal waters, but there was improvement in Virginia tidal waters (ANOVA, F= 11.90, p= 0.0025).


Total Area (Marginal, Degraded, and Severely Degraded)


Area Severely Degraded

Figure 1. Percent (+/- 1 Standard Error) of Chesapeake Bay, Maryland and Virginia tidal waters failing the Chesapeake Bay Benthic Community Restoration Goals (Chesapeake Bay, 1996-2017; Maryland, 1995-2017). Trend of temporal changes tested by ANOVA.

The Potomac River and the mid-Bay main stem were among the Maryland sampling strata in poorest condition in 2017. The upper Bay main stem was in best condition. The Patuxent River showed a significant increasing trend over time in percent area degraded (ANOVA, F= 6.55, p= 0.0183) (Figure 2). In Virginia, the Rappahannock River was in worst condition, with 84% area degraded, and the Virginia main stem was in best condition, with 12% area degraded.

Over the 1995-2017 time series, more than half of the tidal Potomac River (714-1,173 km2) and the Maryland mid-Bay main stem (1,697-2,718 km2) failed the Restoration Goals each year, and a large portion of this area, ranging from 46% to 93% in the Potomac River and 52% to 85% in the main stem, was severely degraded.


Total Area (Marginal, Degraded, and Severely Degraded)


Area Severely Degraded

Figure 2. Percent (+/- 1 Standard Error) of Patuxent River stratum failing the Chesapeake Bay Benthic Community Restoration Goals 1995-2017. Trend of temporal changes tested by ANOVA.

Benthic community degradation in the Chesapeake Bay is extensive. However, all of the Maryland sampling strata except the Patuxent River showed a decrease in degradation in 2017. Hypoxic volume was below the long-term average July through September. Strong winds and below average water temperatures contributed to low hypoxic volume particularly in August 2017. Temperature and winds are significant factors modulating hypoxia, as cooler waters hold more oxygen and wind intensity and direction affect the vertical mixing of the water column. In addition, stream flow and nutrient runoff during the spring contribute to summertime hypoxia in the Bay. Benthic community condition varies from year to year depending on a variety of factors, among which nutrient inputs, variability in stream flow, physical forcing, and the timing of hypoxia play contributing and interacting roles.

 

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Revised: October 3, 2018