Chesapeake Bay Benthic Monitoring Program

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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 in B-IBI have been observed in summer Chesapeake Bay benthic condition between 1985 and 2019.

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Maryland Trends Discussion

Statistically significant B-IBI trends were detected at 14 of the 27 Maryland fixed monitoring sites. Six sites improved (significantly increasing B-IBI score): Upper Bay mainstem (Station 26), Elk River (Station 29), Potomac River at St. Clements Island (Station 51), mesohaline Choptank River (Station 64), Bear Creek (Station 201), and Back River (Station 203). Eight sites declined (significantly decreasing B-IBI score): Baltimore Harbor (Station 22), Patuxent River at Holland Cliff (Station 77), Patuxent River at Broomes Island (Station 71), tidal freshwater Potomac River (Station 36), mesohaline Potomac River at Morgantown (Station 43), deep mesohaline Potomac River at St. Clements Island (Station 52), Nanticoke River (Station 62), and oligohaline Choptank River (Station 66).

Changes in 2019 from 2018 results were limited to the re-appearance of an improving B-IBI trend in the shallow Potomac River at St. Clements Island (Station 51).

Using the last three years of data (2017-2019), the average B-IBI score remained within the same condition category at most sites, improved at 3 sites from failing the goals to meeting the goals, and declined at 5 sites from meeting the goals to failing the goals. Currently, 10 sites meet the Benthic Community Restoration Goals and 17 sites fail the goals. Thus, many of the long-term fixed monitoring sites showed degraded conditions.

Benthic organisms respond to long-term patterns in water quality parameters, such as dissolved oxygen concentrations, phytoplankton concentrations, total nitrogen, sediment loading, and organic loading, in addition to natural fluctuations in salinity and temperature.

Improving trends reflect undergoing basin-wide changes resulting from management actions. Degrading trends reflect the cumulative impacts of nutrient loading and a shift in later years to earlier hypoxia. In Chesapeake Bay, 1998 marks the beginning of a shift in the occurrence of hypoxia, from mid summer (July and August) to early summer (June). This shift coincided with declines in the abundance of many infaunal species.


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Revised: December 9, 2020