Summary of Results

The area of Chesapeake Bay estimated to fail the benthic community restoration goals in 2010 was 6,176 ± 492 km2, or 53% of the tidal Chesapeake Bay bottom. For the Maryland portion of the Bay, the area was 4,182 ± 287 km2, or 67% of the tidal bottom. These estimates were higher than in 2009 but not as high as for 2005-2008. (Figure 1). In 2010 benthic community condition declined (percent area degraded increased) in all the Chesapeake Bay sampling strata except in the Patuxent River and the James River. However, the Patuxent River as well as the Eastern Maryland tributaries, showed a pattern of increasing levels of benthic community degradation over the past several years. (Figure 2).

The increased degradation observed in Chesapeake Bay in 2010 coincided with high river flows. Flow was higher than average in winter (Dec-Jan) and early spring (March), and lower than average in late spring and summer. In March a pulse in river flow coincided with heavy rainfall and large amounts of snowmelt in the Chesapeake watershed. Pulse events bring sudden increases in nutrient and sediment loads into Chesapeake Bay. High spring flows, particularly pulse events, are generally responsible for high nutrient runoff and earlier and spatially more extensive water-column stratification within the Bay, factors that usually lead to more extensive hypoxia (low dissolved oxygen concentrations in the Bay's waters). The Bay has experienced pulse events in the spring of most recent years except 2004 and 2009. The last six years exhibited, on average, lower benthic abundance, lower species richness, and lower B-IBI scores than the previous nine years of the monitoring (Figure 3). Also, at fixed sites in the Maryland main stem and the lower (mesohaline) portion of tributaries, abundance was lower during the 1998-2010 period than during the preceding years (Figure 4). At the same time, and starting in 1998, there was a shift in hypoxia from mid summer to early summer (Figure 5), a sensitive period during the establishment of benthic populations following spring recruitment.

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, 1996-2010; Maryland, 1995-2010). Trend of temporal changes tested by ANOVA.

During the past 16 years, the area with degraded benthic condition has varied with changes in precipitation (dry versus wet years) and year-to-year fluctuations in the frequency, severity, and extent of hypoxia. Years with low run-off (and therefore less nutrient and sediment inputs), fare better for aquatic resources in Chesapeake Bay than years with high run-off. Over the 1995-2010 time series, however, increasing trends in the total area failing the restoration goals (tested by ANOVA, p<0.05) were observed in the Patuxent River and Eastern Maryland tributaries (Figure 2).

Hypoxia is one of the major driving factors in determining benthic condition in the Chesapeake Bay. Excess organic matter in the sediments is also a problem. During the period 1995-2010, the Eastern Maryland tributaries, the James River, and the York River had excess abundance, excess biomass, or both relative to reference conditions in over 20% of the failing sites. Excess abundance and excess biomass are phenomena usually associated with eutrophic conditions and organic enrichment of the sediment in the absence of low dissolved oxygen stress.

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 1995-2010. Trend of temporal changes tested by ANOVA.