Chesapeake Bay Benthic Monitoring Program

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The Upper Bay

Stratum Summary

The upper Bay mainstem receives discharges from the Susquehanna River.  Therefore, water quality in this region reflects pollution sources and inputs from the Susquehanna River watershed.  This stratum generally has low levels of benthic community degradation relative to other bay strata.  Patterns of degradation appear to respond to a mixture of over-enrichment in the upper portion of the stratum (Susquehanna Flats) and hypoxia in deeper areas (segment CB3MH).  In 2003, the upper Bay mainstem exhibited unusual high levels of degradation (chart below), which were associated with high flow conditions in the Bay.  Station 26 in ~3 m of water in segment CB2OH, however, showed a significant positive trend in the B-IBI and good benthic community status in 2003, which did not change with the more extensive hypoxia affecting the bay in 2003.

A high incidence of failure of Restoration Goals due to excess abundance or biomass of organisms is a common feature in the upper bay.  This is indicative of effects on benthos resulting from nutrient enrichment.

The Upper Bay sampling stratum comprises three salinity zones.  The tidal fresh zone (light blue area on map above) includes the freshwater area at the northern end of the Bay, the portion of the Susquehanna River below Conowingo Dam, and the mouth of the Northeast River.  South of this area, from the Sassafras River to the Back River (intermediate blue), low salinity levels determine the oligohaline zone.  The still higher salinity observed in the segment below this (deep blue) results in a mesohaline zone classification.

Note that the stratum receives water from tributaries that are considered to be part of the Eastern Shore or Western Shore basins.  Areas that drain into the Bay through the Susquehanna River or Swan Creek are part of the Upper Western Shore Basin.  The watersheds of the Northeast River and several smaller systems (Still Pond, Worton Creek, and Fairlee Creek) are part of the Upper Eastern Shore Basin. 


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Revised: Sept 10, 2013