Summary of Results

The area of the Chesapeake Bay estimated to fail the benthic community restoration goals in 2011 was 6,386±489 Km2, or 55% of the tidal bottom. For the Maryland portion of the Bay, the area was 4,083±284 Km2, or 65% of the tidal bottom. Maryland’s condition was slightly better in 2011 than in 2010, but within the margin error of the estimate (Figure 1). In 2011 benthic community condition improved (percent area degraded decreased) in the Maryland eastern and western tributaries (except the Potomac River) and the main stem. Benthic community condition declined (percent area degraded increased) in the Potomac, York, and James rivers. Even though there were improvements in some strata, the Potomac River, Patuxent River, and Maryland main stem remained in very poor condition.

The Potomac River was among the most degraded of the Bay sampling strata. The upper Potomac River showed a 19% increase in degradation in 2011 relative to the previous year, and the lower Potomac River below Morgantown exhibited degraded benthic condition in 100% of its area, mostly severely degraded. This is in contrast with previous years which showed declines in the severely degraded condition of the lower Potomac River. Over the 1995-2011 time series, more than half of the tidal Potomac River failed the restoration goals each year, and a large portion of that area ranging from 48% to 93% was severely degraded. Over the same time series, statistically significant increasing trends in percent area degraded were detected in the Patuxent River (ANOVA, F = 18.78, p = 0.0006) and the Maryland Eastern Tributaries (ANOVA, F = 9.99, p = 0.0065) (Figure 2).

Total Area (Marginal, Degraded, and Severely Degraded)

Area Severely Degraded

Figure 1. Percent (+/- 1 Standard Error) of Chesapeake Bay and Maryland tidal waters failing the Chesapeake Bay benthic community restoration goals (Chesapeake Bay, 1996-2011; Maryland, 1995-2011). Trend of temporal changes tested by ANOVA.

Generally better benthic community condition in Maryland tidal waters in 2011 was recorded before and after Hurricane Irene on 27 August 2011 and Tropical Storm Lee on 7 September 2011. The high river flow associated with Tropical Storm Lee decreased salinity and increased sediment loads. Increases in the organic carbon content of the sediments in the Upper Bay main stem, Maryland Western Tributaries, and Patuxent River were observed after the storm. These changes, however, did not have an effect on benthic condition. Results for 2011 suggest no immediate effects of Tropical Storm Lee at sites sampled 1-14 days after the storm. Species composition in areas with the greatest salinity change remained unaltered when compared to species composition in the same areas in 2010.

High spring river flows, particularly pulse events, are generally responsible for high nutrient runoff and earlier and spatially more extensive hypoxia in the Bay’s tidal waters, leading to higher benthic community degradation. River flow in 2011 was high but without strong pulse events until the arrival of Tropical Storm Lee. This factor may have contributed to better overall benthic community condition in Maryland waters in 2011. Another contributing factor may have been the disruption of the pycnocline after Hurricane Irene and increase in the oxygen content of bottom waters. Strong winds associated with Hurricane Irene mixed the water column and caused low dissolved oxygen conditions to completely disappear from main stem waters in late summer, permitting the recovery of the benthic communities.

Total Area (Marginal, Degraded, and Severely Degraded)

Area Severely Degraded

Figure 2. Percent (+/- 1 Standard Error) of Patuxent River and Maryland Eastern Tribs strata failing the Chesapeake Bay benthic community restoration goals 1995-2011. Trend of temporal changes tested by ANOVA.