My name is Jerry McMahon. I am the team leader of the group of U.S. Geological Survey scientists
who are studying the effects of urban development on stream ecosystems.
What is a stream ecosystem? Stream ecosystems include the stream itself, including the water,
the stream channel, and the stream banks, the organisms that live in the stream, and
the organisms including humans that live on the lands that surround and exert an influence
on the stream. Stream ecosystems are complex systems and this complexity is part of what
makes them interesting and valuable.
Anyone walking next to a degraded urban stream can see signs of the effects of urban development.
Over the stream banks, trash hanging in tree branches, discarded shopping carts and tires
and on a warm summer day, mats of algae covering the stream water.
Urban development alters the hydrology, habitat, and water quality of streams. Roads, parking
lots, and buildings increase the impervious cover in urban water sheds, and restrict the
infiltration of precipitation into ground water which increases storm water runoff.
As a result stream flows in urban areas often rise rapidly after a rainfall event. This
rapid increase in stream flow can cause erosion of stream beds and banks and degrade fish
spawning and feeding habitats. Common sources of pollution to urban streams include fertilizers
and pesticides, animal wastes, seepage from septic tanks, liquids from sewage lines, erosion
from construction sites, automobile fluids and vehicle and industrial emissions.
Over the last 10 years, the U.S. Geological Survey's National Water Quality Assessment
Program has examined the effects of urban development on stream ecosystems. The assessment
used the nationally consistent study design in 10 metropolitan areas of the United States.
Urban development significantly affected one or more biological communities in 8 of the
9 metropolitan study areas. Even small levels of urban development had an immediate negative
effect. There is no period of resistance to the effects of urban development. A substantial
decline in its species richness occurred in all but the Denver, Dallas, and Milwaukee
study areas.
Urban development occurred primarily with the conversion of either agricultural or forested
lands.
These two land cover types may mask or escalate the influence of urban development on stream
ecosystems. So, how can this information be used? First, the condition of stream organisms
begins to decline as soon as there is any development within the stream's watershed.
A great deal of caution should be exercised in thinking that there is a safe zone of urban
development. Second, we now know that streams in different regions of the country respond
differently to urban development. Because of these regional differences, management
strategies to protect the character of urban streams that work in one part of the country
may not be effective elsewhere.
For additional information about our project, please visit the project website where you
can obtain both reports, as well as the data used in the project. I am Jerry McMahon, and
on behalf of all my colleagues, I would like to thank you for your interest in understanding
the effects of urban development on stream ecosystems.