The U.S. Geological Survey (USGS) has issued a report of its study of the effects of urbanization on streams. According to the report, urbanization, even in its earliest stages, can degrade streams, damaging support for organisms that depend on those streams. Among the major effects of urbanization are chemical changes, including changes in chloride, nitrogen and herbicides, and flow changes, particularly when streams are channelized or where urbanization results in increased flows when it rains.
The report also found that responses to urbanization by organisms that depend on streams vary across the United States and that different management goals and strategies are necessary in different locations. In general, the report suggests that regional models evaluating multiple stressors can better predict the effects of urbanization at a specific location. Using a model from a New England pilot study, USGS suggested that there was only a 25-percent chance of retaining a healthy stream if urban development covered more than 31 percent of a watershed. But if steps were taken to reduce short-term stream flow changes and improve water quality, there was a 70-percent chance of attaining a healthy stream.