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 2016 (VA Sites from 1985 to 2015).

Maryland Trends Discussion

Statistically significant B-IBI trends were detected at 13 of the 27 Maryland fixed monitoring sites. Four sites improved (significantly increasing B-IBI score): Upper Bay mainstem (Station 26), mesohaline Choptank River (Station 64), Bear Creek (Station 201), and Back River (Station 203). Nine 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), tidalfresh Potomac River (Station 36), mesohaline Potomac River at Morgantown (Station 43), mesohaline Potomac River at St. Clements Island (Station 52), Nanticoke River (Station 62), and oligohaline Choptank River (Station 66).

Changes in 2016 from 2015 results were the appearance of a new declining B-IBI trend in the upper Choptank River (Station 66), the reappearance of a declining B-IBI trend in the Potomac River at St. Clements Island (Station 52), and the disappearance of a declining B-IBI trend in the Potomac River at Morgantown (Station 44).

Using the last three years of data (2014-2016), the average B-IBI score remained within the same condition category at most sites, improved at 4 sites, and declined at 5 sites relative to the 2013-2015 period. For the 2016 reporting year, B-IBI scores decreased at 11 sites and improved at 9 sites. Over the 1985-2016 time series, 11 sites had significant declining trends in abundance, 10 sites had significant declining trends in number of species, and 13 sites had significant declining trends in biomass (Mann-Kendall test results). Thus, many of the long-term fixed monitoring sites showed degrading conditions over time.

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. In 2016, early summer hypoxic volume was low, allowing for recruitment and growth of benthic macroinvertebrates.

 

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Revised: November 29, 2017