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Diagnosing Causes of Benthic Community Degradation in Chesapeake Bay, USA

Daniel M. Dauer 1, Roberto J. Llansó 2, and Michael F. Lane 1

1 Department of Biological Sciences, Old Dominion University, Norfolk, Virginia 23529
2 Versar, Inc., Columbia, Maryland 21045

Chesapeake Bay is North America's largest and most productive estuary. Reductions in nutrient, sediment and contaminant loads were implemented to restore the bay to a more ecologically balanced, productive and diverse ecosystem. As part of this restoration effort, water quality, plankton and benthos have been monitored since 1985.

Benthic macrofauna are an essential component of estuarine monitoring programs. One of the major limitations of macrobenthic community monitoring data is the inability to identify the cause of degraded benthic community condition. We developed a linear discriminant function capable of diagnosing degraded benthic community condition due to sediment contamination with a known inclusion probability.

In developing this sediment contaminant diagnostic tool major challenges were (1) selection of the spatial scale of application of the tool (by sediment type, by salinity regime, over the entire estuarine gradient); (2) selection of the number of stress groups (contaminant stressed, low dissolved oxygen stressed, combined stresses, unknown stresses, etc.); (3) selection of a priori sediment contaminant criteria to develop, calibrate and validate the function; and (4) selection of a metric reduction approach to simply any function developed. We present the final function with recommendations for implementation and interpretation.

Our presentation integrates several accomplishments of the benthic monitoring program (1) development of a benthic index of biotic integrity (B-IBI); (2) establishment of relationships between the B-IBI, exposure variables, and stressor variables; (3) implementation of probability-based sampling to generate areal estimates of degraded benthos; and (4) quantifying the relationship between benthic biotic integrity and benthic habitat quality.

Keywords: Sediment contaminants, benthos, degradation, spatial patterns, diagnostic tools, biotic integrity, and discriminant analysis.

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