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.
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Click on segment areas to see site sampling details.
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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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