Chesapeake Bay Benthic Monitoring Program

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Upper Western Shore Basin Tributaries

Benthic communities in upper western shore basin tributaries (Bush, Gunpowder, and Middle Rivers) were only moderately degraded for the period 1999-2003.  Probabilities of observing degraded benthos in these tributaries ranged from 38 to 41% (Table 1).  The Middle River had the least number of degraded sites among the three tributaries.  Good benthic community condition in the Middle River is consistent with observations of good water quality status for this river.  The Gunpowder showed patterns of degradation over a large area.  In contrast, the Bush River showed degradation in the upper reaches of the estuary.  Degraded sites in the Bush River were numerically dominated by pollution tolerant organisms, mostly tubificid oligochaetes.  This is consistent with excess algal growth and reduced water clarity in this region of the river.


Benthic community condition for Upper Western 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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Table 1.  Total number of sites, degraded sites, and probabilities* (90% confidence limits) of observing degraded benthos, non-degraded benthos, or benthos of indeterminate condition for Upper Western Shore Basin tributaries, 1999-2003.

* Probabilities adjusted according to Agresti and Caffo (2000).  Confidence limits adjusted for segments with ≥ 5 sites.  Exact confidence limits used for segments with < 5 sites.
Note: This latest assessment for the Tributary Teams uses only 5 years of data (1999-2003); methods are described in Llansσ et al. 2003.  Segments are Chesapeake Bay Program subunits having similar salinity and hydrographic characteristics.

 

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URL http://esm.versar.com/vcb/benthos/basins/upwest.htm

Revised: January 21, 2005.