Spatial-scale effects on stream biological integrity: Land use relationships and cost effectiveness of habitat restoration

Spatial scale affects our interpretation of the degree to which land uses in watersheds and their spatial arrangement influence stream habitat and biological integrity. This in turn determines how managers and policy makers approach restoration of degraded streams or protection of existing ones. The first objective of this study was to determine the relationship between the index of biotic integrity (IBI) and forest cover and other habitat variables in the Eastern Corn Belt Plain (ECBP) ecoregion as influenced by spatial scale. The second objective was to determine the cost and the cost effectiveness of recovering IBI scores through habitat restoration. The strongest relationship between IBI scores and forest within watersheds in the ECBP was in the 30 m adjacent to stream segments and 600 m upstream. Habitat variables derived with spatial data provided a stronger prediction of IBI than habitat variables evaluated qualitatively in stream reaches. Forested riparian area and length and steepness of slopes were the two most important predictors of IBI. The ability to predict IBI with habitat variables decreased as the spatial extent of models increased, irrespective of whether watershed or reach habitat variables were used. The cost effectiveness of riparian buffers as a restoration tool decreased with increasing spatial extent and decreasing stream order. As an alternative, in-stream-habitat restoration using half-log structures was less cost effective than riparian buffers at all spatial extents. The cost per 1 percent increase in IBI score weighted by proportion of stream orders was U.S. {dollar}360.10 for a 30-year recovery in the upper Wabash River watershed. The total cost for 100 percent buffer application in the watershed was U.S. {dollar}253,898,769.24, with 96% being the cost of restoring first- to third-order streams. Restoration would increase IBI scores by an average of 9.95% in restored streams. Restoration of low-order streams would accumulate additional water quality benefits downstream that was not quantified. A study of the public's willingness to pay for restoration is recommended.