Chesapeake Bay Benthic Monitoring Program

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Strata Comparison Between a Dry and a Wet Year

Comparison of percent bottom area failing the Chesapeake Bay benthic community restoration goals between 2002 and 2005 by Benthic Monitoring Program strata. 2002 was a dry year in the Chesapeake Bay region, whereas the Bay's tributaries exhibited high spring flows in 2005. In April 2005 heavy rainfall over the Chesapeake Bay contributed to near-record precipitation levels for the month. High spring flows are 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).

In 2002, the percent area failing in the ten Chesapeake Bay strata was generally below 70%, except for the Maryland mid-Bay mainstem (MDM), which includes the deep (>12 m) mainstem trough that is perennially anoxic (devoid of oxygen). In contrast, in 2005 the level of degradation was much higher in the Virginia mainstem (VAM) and the major tributaries: Potomac River (POT), Patuxent River (PAX), Rappahannock River (RAP), and York River (YRK). These systems experience hypoxia. Percent area failing was similar between years in the Maryland upper Western tributaries (MWT) and the Maryland mid-Bay mainstem (MDM), but note the more severe degradation in 2005. The Maryland eastern tributaries (MET) have high agricultural land use and high nutrient input, but low frequencies of low dissolved oxygen events.

The Maryland upper Bay mainstem (UBM) is not generally influenced by hypoxia. In 2005, this stratum had a low percentage of degradation in part because of the distribution of the random sites. Sites with degraded or severely degraded conditions in the Maryland upper Bay mainstem are generally concentrated in deeper water at the mouth of the Chester River. In 2005, no random sites fell in this area, and thus a majority of the sites met the restoration goals.


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Revised: September 9, 2008.