Wednesday, June 6, 2007 - 10:30 AM
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Influence of Small Catchment Size on Maryland's Benthic Index of Biotic Integrity

Ann M. Roseberry Lincoln and Christopher J. Millard. Resource Assessment Service, Monitoring & Non-Tidal Assessment Division, Maryland Department of Natural Resources, Tawes State Office Building, 580 Taylor Avenue, C-2, Annapolis, MD 21401

The Maryland Biological Stream Survey (MBSS) utilizes its Benthic Index of Biotic Integrity (BIBI) as one factor in evaluating stream health. However, freshwater invertebrate assemblages may differ by stream size, due to differences physical habitat and variation in life history. This study evaluates whether or not small catchments (< 300 acres) with minimal outward signs of anthropogenic stress exhibit reduced BIBIs as a result of natural variation in invertebrate assemblage rather than poor condition. Case-control analysis using comparable small and large streams shows that small streams in Maryland’s Highlands region have a significantly lower mean BIBI than large streams. Analysis of variance confirms that the BIBI shows a positive association with catchment size in the Coastal Plain region. Additionally, smaller streams in this region have significantly poorer physical habitat (p < 0.05) than larger streams. These lower scores show a direct relationship with lower BIBIs. For management purposes, Maryland currently treats BIBI scores from small streams identically to large streams. However, this study indicates that small streams with low BIBI scores may not actually be impaired and that additional data should be incorporated into management decisions for those sites.