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 2019 was 6,894 506 km2, or 59% of the tidal bottom (Figure 1). For the Maryland portion of the Bay, the area was 4,240 277 km2, or 68% of the tidal bottom. These estimates indicate an increase in benthic community degradation between 2018 and 2019. Over the 1995-2019 time series, there was no statistically significant trend in percent area degraded in Chesapeake Bay (ANOVA, F= 2.34, p= 0.1407) but there was a decreasing trend in percent area degraded in Virginia tidal waters (ANOVA, F= 7.17, p= 0.0138).


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, 1996-2019; Maryland, 1995-2019). Trend of temporal changes tested by ANOVA.

The Patuxent and Potomac rivers were among the Maryland sampling strata in poorest condition in 2019. 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= 9.29, p= 0.0057) (Figure 2). In Virginia, the Rappahannock River was in worst condition, with 80% area degraded (16% increase from the previous year), and the Virginia main stem was in best condition, with 44% area degraded (36% increase from the previous year).

Over the 1995-2019 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 1995-2019. Trend of temporal changes tested by ANOVA.

All of the Maryland sampling strata except the Upper Bay main stem showed increases in degradation in 2019. The Virginia main stem showed a large increase in degradation. Record stream flows into Chesapeake Bay contributed to record amounts of nutrient inputs, and the summer of 2019 ranked as the third-worst Maryland hypoxia season since monitoring began. Benthic condition varies from year to year depending on a variety of factors, among which nutrient loading, variability in spring river flow, physical forcing (wind intensity and direction), and the timing of hypoxia play contributing and interacting roles.

 

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Revised: November 10, 2020