Maryland Trends Discussion
Statistically significant B-IBI trends were detected at 12 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). Eight 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 (Stations 43 and 44), and Nanticoke River (Station 62).
Changes in 2015 from 2014 results were the appearance of an improving B-IBI trend in Bear Creek (Station 201), and the disappearance of declining B-IBI trends in the mid-Bay mainstem at Calvert Cliffs (Station 001) and the Potomac River at St. Clements Island (Station 52).
A majority of the fixed sites showed increases in abundance, number of species, biomass, and B-IBI scores in 2015. Better benthic community condition in 2015 followed improvements in 2014 and 2013. The observed improvements in benthic condition at the fixed sites were associated with low hypoxia (i.e., higher dissolved oxygen concentrations) in the Bays waters in 2015.
However, over the 1985-2015 time series, 11 sites had significant declining trends in abundance, 13 sites had significant declining trends in number of species, and 12 sites had significant declining trends in biomass.
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 2015, early June hypoxia was very low, allowing for recruitment and growth of benthic macroinvertebrates.