Patapsco/Back River Basin

Benthic community condition in the Patapsco River estuary for the period 1999-2003 was mostly degraded.  The probability of observing degraded benthos was 62% with good confidence (Table 1).  Severely degraded conditions occurred in the upper portion of the estuary, above the Francis Scott Key Bridge and at sites in Curtis Creek, Stony Creek, and along the deep channel south of Sparrows Point.  These areas are affected by very low dissolved oxygen concentrations or toxic contamination.  Excess abundance indicating eutrophic conditions was common in the lower portion of the estuary in areas that are not typically affected by hypoxia.  In previous studies conducted at Versar (Scott et al. 1991, Ranasinghe et al. 1994) benthic community degradation in the Patapsco River was inversely correlated with trace metal concentrations, and sediments from Bear Creek were toxic to the amphipod Leptocheirus plumulosus.

The Back River estuary showed moderately degraded benthic condition with total densities of organisms that were either within the good range or in excess of reference conditions, in agreement with pollution related to excess algal growth and high particulate organic deposition.  In contrast to the Patapsco River, dissolved oxygen conditions in the Back River are usually good.

Fixed long-term monitoring stations in the Patapsco/Back River basin indicated degraded to severely degraded benthic community condition (stations 22, 23, 201, 202, and 203 on map), except for Station 23, which showed improvements in the last three years.  No significant trends in the B-IBI were detected in 2003.

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