Lower Western Shore Basin Tributaries

Benthic community condition in Lower Western Shore Basin tributaries for the period 1999-2003 was best in the Severn River and worst in the South and Magothy Rivers (Table 1).  The Magothy River exhibited degradation in the upper two thirds of the estuary.  Patterns of degradation appeared to respond to a mixture of over-enrichment and hypoxia.  This is consistent with excess algal abundance and observations of low dissolved oxygen concentrations at a shallow, upstream Water Quality Monitoring Program station in the Magothy River.

The Severn River had surprisingly few degraded sites during the 1999-2003 period.  This is in contrast with a previous 1995-2000 assessment, in which the probability of observing degraded benthos was >50%.  In the previous assessment, benthic community degradation in the Severn River was limited to the upper portion of the estuary, where sites had few organisms or were azoic, which was consistent with severe hypoxia or anoxia problems in this region of the river.  Data collected since 1999 shows predominately good benthic community condition.  However, a mid-river fixed monitoring station (Station 204 on map) shows a degrading trend in the B-IBI , which is consistent with a trend in declining bottom dissolved oxygen concentrations.  The South, Rhode, and West Rivers exhibited patterns of degradation predominately due to excess abundance indicative of over-enrichment, consistent with excess algal abundance and reduced water clarity in these three tributaries. 

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Water Quality Map
Segment Analysis

Benthic community condition for
Lower Western Shore Basin sites.
Red = Severely Degraded; Black = Degraded;
Violet = Marginal; Green = Meets Goals
All sites sampled to date (1994-2003) shown.