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. Marylands 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).
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 Bays 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.