The biotic integrity of streams in urban and suburbanizing landscapes

The biological health of lotic communities is negatively correlated with the amount of urban land use in the surrounding watershed. This association is due, in part, to a historic lack of regard for the ecological consequences of development. Environmental considerations are increasingly being brought to the fore in land use planning, and to bear on development in the form of stormwater regulations and best management practices. The effectiveness of these practices in maintaining the biological integrity of receiving waters is assumed, though largely untested. We examined the relationship between urban land use and the biological health of streams in historically urbanized areas of Ohio, USA, and tracked the health of three streams over a decade in the rapidly suburbanizing Columbus, Ohio metropolitan area. The health of streams, as measured by the Index of Biotic Integrity, declined significantly when the amount of urban land use measured as impervious cover exceeded 13.8%, and fell below expectations consistent with Clean Water Act goals when impervious cover exceeded 27.1%. Declining biological integrity was noted in two of the three streams with suburbanizing watersheds at levels of total urban land use as low as 4%, demonstrating that poorly regulated construction practices are the first step toward declining stream health in urbanizing landscapes, and also demonstrate that the current regulatory structure is wanting. The few sites in our data set where biological integrity was maintained despite high levels of urban land use occurred in streams where the floodplain and riparian buffer was relatively undeveloped. An aggressive stream protection policy that prescribes mandatory riparian buffer widths, preserves sensitive areas and minimizes hydrologic alteration needs to be part of the larger planning and regulatory framework.