Summary of Results
The area of the Chesapeake Bay estimated to fail the Benthic Community Restoration Goals in 2015 was 4,428 ± 408 km2, or 38% of the tidal bottom (Figure 1). For the Maryland portion of the Bay, the area was 3,322 ± 291 km2, or 53% of the tidal bottom. These estimates indicate improvements in benthic condition between 2014 and 2015, mostly in Maryland tidal waters. Over the 1995-2015 time series, there were no statistically significant changes in percent degraded area.
Figure 1. Percent (+/- 1 Standard Error) of Chesapeake Bay, Maryland and Virginia tidal waters
failing the Chesapeake Bay Benthic Community Restoration Goals (Chesapeake Bay, 1996-2015; Maryland,
1995-2015). Trend of temporal changes tested by ANOVA.
The Maryland mid-Bay main stem, the Patuxent River and the Potomac River continued to be among the Maryland sampling strata in poorest condition in 2015. However, The Patuxent River showed a large decline in percent area degraded in 2015, from 72% to 48% area degraded. (Figure 2). In Virginia, the York River was in worst condition, with 56% area degraded.
Over the 1995-2015 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. Over the same time series a significant increasing trend in percent area degraded was detected in the Patuxent River (ANOVA, F = 9.92, p = 0.0053). Significant increasing trends in percent area severely degraded were detected in the Patuxent River (ANOVA, F = 4.96, p = 0.0382) and Maryland Eastern Tributaries (ANOVA, F = 3.34, p =0.0836).
Figure 2. Percent (+/- 1 Standard Error) of Patuxent River stratum failing the Chesapeake Bay
Benthic Community Restoration Goals 1995-2015. Trend of temporal changes tested by ANOVA.
Improved benthic condition in 2015 can be attributed to low hypoxic volumes in Chesapeake Bay in 2015, which were likely the result of low streamflow and nutrient runoff during the spring. Susquehanna River flow at Conowingo was very low January through early March, increased above the normal range of streamflow in April, and decreased again through mid June. Hypoxic volume in 2015 was below average throughout most of the summer, but most importantly, hypoxic volume was very low during the first half of June. May and June are sensitive periods for the development of benthic communities as recruitment and growth of macroinvertebrates take place during this time.