Abstract
Methods for the conservation of stream habitat and biodiversity at the watershed scale have not been developed. Watersheds span large land areas, encompass a connected range of stream sizes, and integrate natural and altered properties of a drainage area. Methods are needed to identify the locations of high biodiversity in watersheds, compare aquatic biodiversity distributions among regions, and provide watershed-scale information useful for targeting conservation measures. The National Biological Service (USA) in cooperation with other Federal and State agencies developed geographic information system (GIS) methodology called Gap Analysis to identify the distribution of biodiversity over large spatial areas. To date, it has been used to address only terrestrial conservation needs. We are developing an aquatic version of the Gap Analysis in the Allegheny River drainage in western New York State to define the methodology and evaluate the feasibility of predicting biodiversity distribution at the watershed scale. Our standardized stream reach accounting system is based on the U.S. Environmental Protection Agency Reach File 3 System. Each stream reach is classified into one of 18 habitat types for fish faunal predictions and one of 8 habitat types for invertebrate faunal predictions. Habitat types were defined using the following sets of physicochemical attributes: stream size (headwaters, large streams/small rivers, large rivers), physical habitat (dominated by natural geomorphological processes, moderately altered, and dominated by human structures and controls), water quality (suitable for life support, biologically stressful), gradient (steep, low slope) and riparian forest cover (closed canopy over channel, open channel). Stream size was determined from drainage area using the GIS. Physical habitat, reach gradient, and riparian forest cover were classified from topographic and land use maps. Physicochemical data from the U.S. Environmental Protection Agency STORET database provides a means to classify water quality. Using our habitat typing system, we predict that the highest fish diversity will be found in medium size streams with natural fluvial channels and good water quality, whereas the most reduced fish faunas will be found in large rivers with highly modified channels and poor water quality. For invertebrates, we predict that the greatest diversity (in terms of ecological function groups) will be in small and medium size streams with primarily a closed canopy, steep gradient, and good water quality. Our GIS modeling effort succeeded in predicting the expected distribution of fish and invertebrate diversity at the watershed scale. Adequate biological and physicochemical data appear available and compatible with watershed-scale GIS programs. We also have extensive biological survey data that provides an independent means to testing the validity of our biodiversity predictions.