Upper Eastern Shore Basin Tributaries
During the period 1999-2003, the Northeast River, Bohemia River, Sassafras River,
and Eastern Bay were in worst condition, with a >50% probability of observing
degraded benthos (Table 1). Benthic community
condition in the Elk River was
largely indeterminate, but not particularly degraded. Confidence intervals
for these estimates were generally broad (Table 1).
The Chester River oligohaline condition was largely indeterminate, and for the
tidal freshwater region there were insufficient samples to produce any reliable
estimate. The Chester River mesohaline region showed a relatively high
probability of degraded benthos (48%, Table 1). Most
of the sites with failing
B-IBI were concentrated in the lower portion of the river, around Eastern Neck
Island. Poor benthic community condition in this region may be
attributed to stress from low dissolved oxygen. However, fifty percent
of the sites in this region
exhibited excess abundance of organisms, indicative of enriched conditions
consistent with degrading trends in algal abundance and water clarity. A
fixed long-term monitoring station located mid-river above the region where
a majority of the probability sites failed, had good benthic community status
and no significant trend in the B-IBI (station 068 on map).
The fixed station in the Elk River exhibited a significant positive trend in the
B-IBI, but marginally degraded benthic community in 2003 (station 029 on map). The
improving trend was associated with a decrease in the abundance of oligochaete
worms and an overall increase in the density of bivalves. Improving trends in
the Elk River are reported for algal abundance and the status of most water
quality parameters is good. Benthic community dynamics in the Elk River are
probably influenced by over-enrichment resulting from algal growth, but also by
patterns in river flow and the associated salinity fluctuations.
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Water Quality Map
Segment Analysis
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Benthic community condition for
Upper Eastern Shore Basin sites.
Red = Severely Degraded; Black = Degraded;
Violet = Marginal; Green = Meets Goals
All sites sampled to date (1994-2003) shown.
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