LANDSCAPE INFLUENCES ON STREAM BIOTIC INTEGRITY ASSESSED AT MULTIPLE SPATIAL SCALES

The biological integrity of stream ecosystems depends critically on hu man activities that affect land use/cover along stream margins and pos sibly throughout the catchment. We evaluated stream condition using an Index of Biotic Integrity (IBI) and a habitat index (HI), and compare d these measures to landscape and riparian conditions assessed at diff erent spatial scales in a largely agricultural Midwestern watershed. O ur goal was to determine whether land use/cover was an effective predi ctor of stream integrity, and if so, at what spatial scale. Twenty-thr ee sites in first-through third-order headwater streams were surveyed by electrofishing and site IBIs were calculated based on ten metrics o f the fish collection. Habitat features were characterized through fie ld observation, and site HIs calculated from nine instream and bank me trics. Field surveys, aerial photograph interpretation, and geographic information system (GIS) analyses provided assessments of forested la nd and other vegetation covers at the local, reach, and regional (catc hment) scales. The range of conditions among the 23 sites varied from poor to very good based on IBI and KI scores, and habitat and fish ass emblage measures were highly correlated. Stream biotic integrity and h abitat quality were negatively correlated with the extent of agricultu re and positively correlated with extent of wetlands and forest. Corre lations were strongest at the catchment scale (IBI with % area as agri culture, r(2) = 0.50, HI with agriculture, r(2) = 0.76), and tended to become weak and non-significant at local scales. Local riparian veget ation was a weak secondary predictor of stream integrity. In this wate rshed, regional land use is the primary determinant of stream conditio ns, able to overwhelm the ability of local site vegetation to support high-quality habitat and biotic communities.