Trends in Fixed Site Benthic Condition

Forty-eight sites in areas targeted for pollution abatement and other management actions are monitored annually by the Benthic Monitoring Program to assess whether benthic community condition is changing.  The illustration below shows where significant improving (green) and degrading (red) trends have been observed in summer Chesapeake Bay benthic condition between 1985 and 2005.

Summary results:
• Maryland Trends Discussion

Individual site results:
• Interactive Map
• Site Locations (Coordinates)

Statistically significant B-IBI trends (p<0.1) were detected at 8 of the 27 sites currently monitored. Trends in benthic community condition declined at 3 sites (significantly decreasing B-IBI trend) and improved at 5 sites, as in 2004. Trends detected through 2004 were still present in 2005 at 7 sites. One trend that just emerged in 2004 disappeared with the addition of the 2005 data (Baltimore Harbor Sta. 23), and one trend that disappeared in 2004 was again significant in 2005 (Elk River Sta. 29).

Sites with improving B-IBI trends were located in the main stem of the Bay (Sta. 15 and 26), Elk River (Sta. 29), Choptank River (Sta. 64), and Potomac River at St. Clements Island (Sta. 51). Sites with degrading B-IBI trends were located in the Severn River (Sta. 204), Patuxent River at Holland Cliff (Sta. 77), and Nanticoke River (Sta. 62). Many of the trend sites showed reduced B-IBI scores in 2005 relative to the previous year. Lower B-IBI scores were obtained at locations prone to hypoxia such as at trend sites in Baltimore Harbor, Back River, Severn River, and lower Patuxent and Potomac rivers. None of the trend sites in the eastern shore tributaries of Maryland showed declines in B-IBI status in 2005.

Benthic organisms respond to long-term patterns in water quality parameters, such as dissolved oxygen concentrations, chlorophyll a, total nitrogen, and sediment loadings, in addition to natural fluctuations in salinity. Improving trends are likely to reflect undergoing basin-wide changes resulting from management actions, such as improvements to reduce nutrient inputs, chlorophyll, and sediment concentrations in the Elk River basin. Degrading trends reflect the cumulative impacts of pollution loadings in regions with significant problems that are not yet responding to pollution abatement.

The degrading trend in the Severn River was associated with a decrease in biomass of organisms. The upper portion of the Severn River is affected by severe hypoxia. The Nanticoke River is affected by high sediment loads. Low biomass relative to the reference condition is a problem common to the Nanticoke River and the other tributaries of the lower eastern shore of Maryland.