The Effects of Urbanization on Local First-Order Streams: One Year Later
Kristen K. Cecala, Steven J. Price, William Ringle, and Michael E. Dorcas
Overall, we found that large-scale land clearing is prevalent and occurring rapidly throughout this region, often with little consideration for maintaining functional catchments. Previous studies have shown that these watersheds are critical for maintaining water quality locally and at larger scales (House et al. 1993). Our data also show that irrespective of buffers that developers maintain, developers frequently must build roads or other passages over the stream directly impacting the downstream areas of the streams. Although not presented in this analysis, there appears to be a trend towards greater quantities of fine sediments within streams following direct stream impaction.
Our data support hypotheses predicting a lag time between watershed disturbance and the appearance of stream impacts. Furthermore, although just the loss of forests can greatly impact streams, the creation of impervious surfaces, use of lawn fertilizers, and pesticides after inhabitation of the area may affect streams more than simple land clearing. Because we only examined 10 streams, conclusions about the patterns occurring throughout the landscape are difficult to form because high variation occurs among sites. Despite few significant trends, we do see that some predicted changes are beginning to occur after just the first year of watershed disturbance. First, we see that dissolved oxygen within a stream decreases after the first year of disturbance, and conductivity appears to increase with urbanization. Although the conductivity trend was non-significant, this relationship is a positive increase at every site indicating that conductivity as a measure of metals within the water increases with land clearing and erosion. Furthermore, while non-significant, an increase in fine sediments, also likely caused by increased erosion, seems to be positively correlated with increased proportions of disturbed watersheds.
We conclude that after one year of disturbance, consequences of urbanization and land clearing are minimal within streams. Thus, the effects of development on streams appear to be long-term causes and a long-term problem. These long-term effects on streams are particularly important to consider when examining the persistence of organisms within streams. Dissolved oxygen is particularly important for maintaining stream organisms, and a decrease in dissolved oxygen may yield reduced abundances or reduced fitness of surviving stream organisms. Furthermore, changes in substrate, especially increases in fine sediments, can eliminate interstitial spaces crucial for refugia of a variety of species (Borchardt and Statzner, 2000). Lastly, stream organisms play a large role in nutrient cycling within streams, and if these species are eliminated from urbanized streams, the cumulative effects of increased carbon and nitrogen merging in larger water bodies can have critical impacts on human lives (Chesapeake Bay Program).
Further studies within these Piedmont stream networks is imperative to understand the long-term impacts rapid urbanization in this region will have upon the future of our overall water quality. Examining specific aspects of urbanization such as development of steep slopes or buffer zones are becoming more important to better compromise between necessary growth and water quality protection. Furthermore, although not described in this study, descriptions about ways to mediate the risks of creating impervious surface and using fertilizer and pesticides are needed. These research projects are necessary to preserve the quality of water today and in the future. We must learn lessons from large-scale die-offs occurring in larger water bodies due to large scale urbanization throughout their watersheds.
For more information regarding one major watershed restoration program, see the Chesapeake Bay Program.
|Davidson College Herpetology Laboratory|
Questions? Email: Krcecala@davidson.edu