Summary of Results

The area of Chesapeake Bay estimated to fail the benthic community Restoration Goals in 2005 was 6,828 (±503) km², or 59% of the tidal Chesapeake Bay bottom. This figure represents a substantial increase over that of 2004. In 2004, 47% of the tidal Chesapeake Bay bottom was degraded. Degradation in 2005 was as high as in 2003, both years showing the largest estimates of degraded area since baywide monitoring began in 1996.

The higher estimates for 2003 and 2005 were associated with high spring flow conditions in Chesapeake Bay, which were responsible for high nutrient and sediment runoff, strong water column density stratification events, and widespread hypoxia (low dissolved oxygen). River flow was also above normal in 2004, but the heaviest precipitation occurred in September, after the summer period that usually influences most benthic community condition in the Bay.

Regardless of the wet vs. dry year variability, benthic community degradation in Chesapeake Bay is large relative to the reference condition. Forty percent of the tidal Chesapeake Bay bottom in 2005 (4,664 km²) was severely degraded, 13% (1,550 km²) was degraded, and 5% (614 km²) was in marginal condition. The severely degraded estimate includes the area of the mainstem of the Bay that is deeper than 12 m (the "deep trough"), which is perennially anoxic (not enough oxygen to sustain life).

Among the ten Bay strata, the Potomac (POT), Patuxent (PAX), and Rappahannock (RAP) rivers were in the poorest condition in 2005. The Maryland mainstem (MDM) also exhibited high levels of degradation. Compare these levels with the 2002 estimates of percent degraded area (second chart), which show more typical conditions in the tributaries.

In 2005, percent degradation in the upper Bay mainstem (UBM) was very low in part because of the distribution of the random sites. Sites with degraded benthic condition in the upper Bay mainstem are generally concentrated in deep water at the mouth of the Chester River. In 2005 there were no random sites in this area, and thus a majority of the sites in the stratum met the Restoration Goals. The upper Bay mainstem above the Chester River is not generally influenced by hypoxia.