Abstract
A proximity‐based measure of land‐use impacts to aquatic ecosystem integrity based on both the relative abundance and spatial distribution of land uses within a watershed is developed and evaluated. This hydrologic proximity measure assumes that the impact of the land use at a specific position in the watershed upstream from a sample site is related to the relative volume of water that would be expected to flow through that position during a storm event. In order to evaluate the utility of this measure, the fit of several models based on land use and habitat assessment measures to biological integrity data is compared to the fit of a similar model based on hydrologic proximity measures. This hydrologic proximity model explained more of the variability in observed Hilsenhoff biotic index scores (R^2^ = 0.92) than land use impacts estimated as the watershed surface area occupied by each land use (R^2^ = 0.83), U.S. Environmental Protection Agency habitat assessment methods (R^2^ = 0.68), or Ohio Environmental Protection Agency habitat assessment methods (R^2^ = 0.68). Additionally, an algorithm based on the hydrologic proximity measure is presented for optimizing land use conversion projects to enhance biological integrity.