Degradation of stream habitats and declines in fish populations often are associated with human alteration of landscapes. Within watersheds heavily influenced by human activities, such as those of the agricultural midwestern United States, the conservati on and restoration of riparian vegetation provide a potential means for the maintenance of stream ecosystem integrity. This study evaluated the influences of landscape and riparian conditions on a stream ecosystem by assessing stream habitats and fish assemblag es at sites within the River Raisin of southeastern Michigan. The River Raisin, flowing through forested and agricultural lands typical of midwestern watersheds, is nonetheless noted for its high aquatic diversity. Relationships were examined among watershed land use, riparian vegetation at multiple scales, and stream ecological integrity as quantified by indices based on fish assemblages and habitat characteristics.

Methods were developed to quantify streamside vegetation at three spatial scales for sites within the River Raisin of southeastern Michigan. Field surveys, aerial photograph interpretation, and geographic information system (GIS) analyses provided ass essments at scales of the local site, stream reach, and entire stream subbasin. Local riparian conditions ranged from virtually no vegetation to extensive coverage at both site and reach scales. At the subbasin level, agriculture accounted for 2 to 99% o f land use within riparian zones, while wetland cover ranged from 0 to 47%.

The Index of Biotic Integrity (IBI) was calculated for twenty-three sites in first- through third-order headwater streams that were surveyed by electrofishing. Habitat features were characterized through field observation. Site-specific watershed lan d uses were quantified using a GIS. The IBI indicated a range of poor to good stream conditions. Two metrics--the number of species and number of intolerant species--made the greatest contributions to total IBI scores. The IBI showed a negative correla tion with the extent of agriculture and positive correlation with the extent of wetlands within a site-specific watershed. A strong negative correlation was found between the habitat index and the extent of agriculture within a site-specific watershed. At the broadest scale of riparian analysis, the subbasin level, riparian land cover was strongly correlated with IBI or habitat scores; however, sites lacking adequate riparian coverage at the local site tended to have low habitat scores. In general, loc al vegetation factors were less effective than broader regional measures in explaining the variability among IBI and habitat scores. In the River Raisin, land use and riparian conditions at the subbasin scale may overwhelm the ability of local site veget ation to support high-quality habitat and biotic communities. Broader riparian coverage along an entire stream corridor may provide functions important to the maintenance of stream ecosystem integrity