We all would guess that levels of native fish and aquatic insects would decline as an area becomes increasing built up, but a new study has shown that this level is much lower than previously thought.
The study, which was conducted by the U.S. Geological Survey, found that even at urbanisation levels previously thought to protect stream communities there was some effect on the aquatic life.
Concrete, tarmac and other urban land cover allows water to quickly run off into the streams, and the subsequent rise in water levels and fluctuations in temperature can be harmful to fish and other aquatic life. This runoff can also contain the fertilisers and pesticides used on grass.
Tom Cuffney, a USGS biologist is quoted saying:
"When the area of driveways, parking lots, streets and other impervious cover reaches 10 percent of a watershed area, many types of pollution sensitive aquatic insects decline by as much as one third compared to streams in undeveloped forested watersheds. We learned that there is no 'safezone,' meaning that even minimal or early stages of development can negatively affect aquatic life in urban streams."
The study examined nine urban areas across the including Boston, Dallas, Salt Lake City and Atlanta and found that in eight of the nine cases urbanisation had had a negative impact on at least one or more biological communities. The largest impact was found to be on ‘macroinvertebrates’, examples of which include crayfish, mussels, aquatic snails, aquatic worms, and the larvae of aquatic insects.
The study also found that there was a much lower impact on aquatic life when areas that had previously been used for agriculture compared to areas where previously forested areas were flattened to make way for buildings. In addition for fish in particular the study found that reserviours can be particularly disruptive acting as physical barriers to migration and populations as well as a source of ‘alien’ species that can disrupt native assemblages.
Although a lot of this may seem rather obvious to the ‘man on the street’, this study does represent an integrated approach to understanding the physical, chemical and biological impacts on urban streams. The USGS hope that this will be used for prioritising strategies for stream protection and restoration and in evaluating the effectiveness of those strategies over time.
For example Tom Schueler, Chesapeake Stormwater Network coordinator is quoted: "Stream protection and management is a top priority of state and local officials, and these findings remind us of the unintended consequences that development can have on our aquatic resources. The information has been useful in helping us to predict and manage the future impacts of urban development on streams and reinforces the importance of having green infrastructure to control storm-water runoff and protect aquatic life."