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 2016 was 5,271 379 km2, or 45% of the tidal bottom (Figure 1). For the Maryland portion of the Bay, the area was 4,148 293 km2, or 66% of the tidal bottom. These estimates indicate declines in benthic condition between 2015 and 2016, mostly in Maryland tidal waters. Over the 1995-2016 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= 9.31, p= 0.0066).


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, 1996-2016; Maryland, 1995-2016). Trend of temporal changes tested by ANOVA.

The Potomac River, Maryland Upper Western Tributaries, and Maryland mid-Bay mainstem were among the Maryland sampling strata in poorest condition in 2016. The Patuxent River showed a significant increasing trend over time in percent area degraded (ANOVA, F= 5.16, p= 0.0343). However, degradation declined in 2015 and 2016 from 72% to 48%. (Figure 2). In Virginia, the James River was in worst condition, with 68% area degraded.

Over the 1995-2016 time series, more than half of the mid-Bay main stem (1,697-2,718 km2) and the tidal Potomac River (714-1,173 km2) failed the Restoration Goals each year, and a large portion of this area, ranging from 52% to 85% in the main stem, and 46% to 93% in the Potomac River, 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 1995-2016. Trend of temporal changes tested by ANOVA.

The decline in benthic condition in 2016 can be attributed to high hypoxic volumes in Chesapeake Bay in 2016. High hypoxic volumes were likely the result of prolonged warm temperatures and lack of significant winds in late July. Temperature and winds are significant factors modulating hypoxia, as warmer waters hold less 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 condition varies from year to year depending on a variety of factors, among which nutrient loading, variability in stream flow, physical forcing, and the timing of hypoxia play contributing and interacting roles.

 

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URLhttp://esm.versar.com/vcb/benthos/results/summary.htm

Revised: November 29, 2017