Development of a provisional physical habitat index for Maryland freshwater streams.

Provisional physical habitat indices were developed and validated for Maryland Coastal and Non-Coastal Plain streams using variables (commonly called metrics) that best discriminated reference and degraded conditions based on biological, chemical and land use data from the 1994-97 Maryland Biological Stream Survey (MBSS). These habitat indices contained variables that described structural, hydrological, vegetative and aesthetic components of stream habitat. Variables with the best discriminatory power for Coastal Plain streams were: instream habitat, velocity/depth diversity, pool/glide/eddy quality, embeddedness, maximum depth and aesthetic rating. Physical habitat variables with the best discriminatory power for Non-Coastal Plain sites were: instream habitat, velocity/depth diversity, riffle/run quality, embeddedness, number of rootwads and aesthetic rating. The overall classification efficiency for index validation was 76% for both indices pooled over both strata. Scaled physical habitat index values (0-100) for both strata identified nearly twice as many good sites (31%) as very poor sites (16%). More than half the Maryland sites were in the poor to fair range (53%).