EDITORS NOTE:

This week, we’re sharing an article from the USGS on research focusing on development and stream impacts–namely the adverse effects on aquatic biota. The article has major implications for stormwater management:

More development means more impervious cover means more water impacts means less aquatic life.

Sounds reasonable. These research results have been played out time and again; they have been communicated by well-respected sources such as the Center for Watershed Protection over many years, and argued by stormwater experts such as the Center’s former director, Tom Schueler. And they send an important message.

But, we feel the need to insert an important caveat here – lest these research findings be used to condemn all development and equate any sort of higher density development as inimical to stream life. After all, don’t we continue to maintain in other contexts that the “city” is the ultimate BMP?! The message here must be understood to include an important qualification:

More development using the same conventionally flawed stormwater practices (or none at all) means more impervious cover means more water impacts means less aquatic life.

This is critical. Evaluate the details of the USGS research more closely (metropolitan areas in Boston, Raleigh, Atlanta, Birmingham, Milwaukee-Green Bay, Denver, Dallas-Ft. Worth, Salt Lake City, Portland Oregon). Because the watersheds of the streams being studied include all types of development, much of it older, and because much of this watershed development suffers from no stormwater management whatsoever (in some older cases) or, alternatively, inadequate stormwater management (i.e., simple detention),we need to be very careful about drawing conclusions. What we lack are the results from higher density development using optimal or close to optimal stormwater management systems.

Our BMP manuals make the case for substantial quality and quantity performance for many BMPs. Although few give us 100 percent performance, the argument can be made that with intensive use of both non-structural and structural BMPs, impacts to streams and aquatic life can be dramatically reduced, minimized. Particulate and solubilized nonpoint source pollutant loads can be kept to modest levels. Natural instream hydrology can be nearly mimicked. Pre-development temperature regimes can be almost maintained.

Density is not a dirty word - just the reverse. The “city” is the ultimate BMP. Load as much human-related development into the most compact form (the “city”) as is feasible – using state-of-the-art BMPs (see green infrastructure and all the rest). Retain as much undisturbed area surrounding the “city” in perpetuity. And human life and aquatic life can achieve balance. We must be very careful not to conclude that low density development with impervious cover less than 10 percent, including extremely large-lot residential subdivisions is the ultimate solution to stormwater management/watershed management problems. Such a mindset translates - net -into vastly more land disturbance and vastly more impervious cover and vastly more nonpoint source pollutant loads with vastly more stormwater flow.

For the USGS  discussion, Aquatic Life Declines at Early Stages of Urban Development, go here>>

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The number of native fish and aquatic insects, especially those that are pollution sensitive, declines in urban and suburban streams at low levels of development - levels often considered protective for stream communities, according to a new study by the U.S. Geological Survey.

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.

–Tom Cuffney, USGS biologist

As a watershed becomes developed, the amount of pavement, sidewalks and other types of urban land cover increases. During storms, water is rapidly transported over these urban surfaces to streams. The rapid rise and fall of stream flow and changes in temperature can be detrimental to fish and aquatic insects. Stormwater from urban development can also contain fertilizers and insecticides used along roads and on lawns, parks and golf courses.

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 stormwater runoff and protect aquatic life.

–Tom Schueler, Chesapeake Stormwater Network

USGS studies examine the effects of urbanization on algae, aquatic insects, fish, habitat and chemistry in urban streams in nine metropolitan areas across the country: Boston, Mass.; Raleigh, N.C.; Atlanta, Ga.; Birmingham, Ala.; Milwaukee-Green Bay, Wis.; Denver, Colo.; Dallas-Fort Worth, Texas; Salt Lake City, Utah; and Portland, Ore.

These USGS studies also show that land cover prior to urbanization can affect how aquatic insects and fish respond to urbanization. For example, aquatic communities in urban streams in Denver, Dallas-Fort Worth and Milwaukee did not decline in response to urbanization because the aquatic communities were already degraded by previous agricultural land-use activities. In contrast, aquatic communities declined in response to urbanization in metropolitan areas where forested land was converted to urban land, areas such as Boston and Atlanta.

Comparisons among the nine areas show that not all urban streams respond exactly the same. This is mostly because stream quality and aquatic health reflect a complex combination of land and chemical use, land and storm-water management, population density and watershed development, and natural features, such as soils, hydrology, and climate.

These USGS studies represent an integrated approach to understanding urban streams that includes physical, chemical and biological characteristics associated with urbanization. This is critical for prioritizing strategies for stream protection and restoration and in evaluating the effectiveness of those strategies over time.

For more information, listen to USGS Corecast Episode 127.

The full report and extended video podcasts are available at the National Water Quality Assessment program urban studies website.

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