USGS Multimedia Gallery: (Video)--The Effects of Urbanization on Stream Ecosystems (extended) Part I: Introduction

Jerry McMahon: My name is Jerry McMahon. I’m the team leader of a group of US Geological Survey Scientists who are studying the effects of urban development on stream ecosystems. In the podcast today, we’re going to give an overview of the project including a description of study objectives, our approach to doing the study and several of the important findings related to the effects of urban development on stream biota. What is a stream ecosystem? Stream ecosystems include the stream itself, including the water, the stream channel and the stream banks, the organisms that leave 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. For example, humans enjoy the beautiful sights and sounds of healthy streams from the buzzing of dragonflies to the calls of birds that feed on the insects and fish living in the water. The diverse communities of aquatic biota such as algae, aquatic insects and fish that live in a healthy stream helps sustain a balanced and adaptive ecosystem of plant and animal community. A healthy stream ecosystem in turn provides important benefits to humans ranging from recreational and aesthetic services to supporting the diversity and sustainability of other linked ecosystems. It’s also true that many urban stream ecosystems are degraded below a level that’s considered desirable by the public.
Anyone watching next to a degraded urban stream can see signs of the effects of urban development. Eroded stream bank, 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 watersheds 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 used on lawns, gardens and along roadways. Animal waste, seepage from septic tanks, leakage from sewage lines, erosion from construction sites, automobile fluids and vehicle and industrial emissions. The human footprint has expanded during a century and a half of almost continuous urban development in the United States. Four-fifths of Americans now live in metropolitan areas and the advantages and challenges of living in these developed areas convenience, congestion, employment, pollution are part of the day to day realities of most Americans. Evidence of this human footprint is illustrated in these maps showing the expansion of urban land in the Atlanta Metropolitan area.
This area recorded phenomenal growth during the 1990’s where an average of 69,000 people moved into the metropolitan area each year. With most of the population growth occurring outside the city limits, the amount of urban land in the metro area increased by 50% during this period. According to some estimates, almost 50 acres of tree cover were lost every day during the 1990’s.
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’m Jerry McMahon and on behalf of all my colleagues, I’d like to thank you for your interest in understanding the effects of urban development on stream ecosystems.