The Effects of Urbanization on Local First-Order Streams: One Year Later

Kristen K. Cecala, Steven J. Price, William Ringle, and Michael E. Dorcas

Davidson College

Literature Cited
Anthropology Department
Davidson College Herpetology Laboratory
Kristen Cecala's Website

Throughout the world, the human population is increasing rapidly with matching growth of urbanization, which is extremely evident within the United States. Urban sprawl is particularly characteristic of many rapidly growing areas in the southeastern area of the country. Throughout the world, over 60% of the population lives within heavily urbanized areas, although only 2% of the world’s surface is covered in urbanization (Paul and Meyer 2001). While this proportion of urban land sounds minor, the consequences of this land use have been and will continue to be much greater than any other type of land use practice (Folke et al. 1997). For example, over 78% of greenhouse gases are produced from this 2% of urban land use (Grimm et al. 2000). We must also consider that urbanization is a relatively permanent aspect of our landscape. Agricultural fields can be rapidly recolonized by native plants and trees, but urbanization is rarely reclaimed by natural land. Instead, humans continue to inhabit and use these lands before further expanding.

The effects of urbanization on stream ecosystems are known to be critical, and in 2001, 130,000 km of streams and rivers throughout the United States were impacted by urbanization (USEPA 2000). Construction of new urban landscapes has the potential to alter streams in multiple ways. Urbanization primarily increases impervious surfaces throughout a watershed that increases erosion and runoff of metals, chemicals, and increases the diversity and abundance of aquatic pathenogens. Increased runoff of surface water yields increased flow rates and shorter flood events during storms than in streams with natural watersheds. Because of shorter lag times between when water falls until it enters the stream, not only do input volumes increase, but water temperature increases within streams. Increased flow velocities on land cause more erosion and augment the levels of silt and clay within stream substrates. The variation in substrate also can change the width and depth of streams further impacting stream water temperature. Because of increased temperatures, detrital processing in urban streams is known to be more rapid than in natural streams. Furthermore, increased flow rates during flood events yield a reduction in detritus within streams. Lastly, these changes are indirect resulting from the process of urbanization, but we must also consider the direct effects of urbanization on streams such as bridges, culverts, and riprap added to streams in order to allow for urban development (Summarized by Paul and Meyer 2001).

While alteration of the physical structure of streams does not initially seem to be extensive, researchers must also consider the effects these changes will have on local flora and fauna as well as larger waterbodies. Stream networks are dendritic in which the consequences of impacted first-order streams can be seen throughout the watershed ultimately yielding changes in rivers or bays such as the Chesapeake Bay (Chesapeake Bay Program). Within first-order streams, fish, invertebrates, and salamanders depend on detritus as well as interstitial spaces for refugia and prey. As debris is pushed downstream by increase flow velocities and interstitial spaces are filled by silt and clay, these organisms have difficulty persisting within these environments. Furthermore, the increased velocities of streams can cause downstream drift in which animals are forced downstream. Lastly, these velocities may also prevent animals from re-colonizing these areas yielding local extinctions of organisms.

The Charlotte, North Carolina, metropolitan area is the 6th fastest growing region in the country. Rapid urbanization can be found throughout Mecklenburg and Cabarrus counties as urban sprawl extends from Charlotte. Because this area is adjacent to Davidson College, we have the opportunity to learn more about how urbanization is affecting the landscape. We examined how urbanization has affected physical stream characteristics one year following watershed disturbance. We hypothesize that urban development will begin to impact streams within the first year following disturbance. We investigated whether the urbanized proportion of the watershed predicts changes in stream characteristics, and whether buffers can mediate stream characteristic changes.
This project was completed as part of the requirements for an independent study course in the Anthropology Department at Davidson College in conjunction with work for the Davidson College Herpetology Laboratory. Support for this project was provided by the Department of Biology, Duke Power, and by a National Science Foundation Grant (DEB-0347326) to M. Dorcas. We would like to thank all of the private landowners and developers who have allowed us to sample on their properties as well as all the Davidson College Herpetology Laboratory members over the past 2 years who have assisted with data collection.
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