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 have been observed in summer Chesapeake Bay benthic condition between 1985 and 2017.

Maryland Trends Discussion

Statistically significant B-IBI trends were detected at 15 of the 27 Maryland fixed monitoring sites. Five sites improved (significantly increasing B-IBI score): Upper Bay mainstem (Station 26), mesohaline Choptank River (Station 64), shallow Potomac River at St. Clements Island (Station 51), Bear Creek (Station 201), and Back River (Station 203). Ten sites declined (significantly decreasing B-IBI score): Baltimore Harbor (Station 22), Curtis Creek (Station 202), 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), oligohaline Choptank River (Station 66), and Chester River (Station 68).

Changes in 2017 from 2016 results were the appearance of a new declining B-IBI trend in the Chester River (Station 68), and the appearance of a new improving B-IBI trend in the shallow Potomac River at St. Clements Island (Station 51).

Using the last three years of data (2015-2017), the average B-IBI score remained within the same condition category at most sites, improved at 2 sites, and declined at 5 sites relative to the 2014-2016 period. For the 2017 reporting year, B-IBI scores improved at 9 sites and declined at 8 sites. Currently, 11 sites meet the Benthic Community restoration Goals and 16 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: October 17, 2018