Landscape characteristics and North Carolina stream life: A multiple-scale ecological risk assessment of nonpoint source pollution

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Title: Landscape characteristics and North Carolina stream life: A multiple-scale ecological risk assessment of nonpoint source pollution
Author: Potter, Kevin Mark
Advisors: Dr. George R. Hess, Committee Member
Dr. Frederick W. Cubbage, Committee Chair
Dr. Gary B. Blank, Committee Member
Abstract: Nonpoint sources of pollution may be responsible for as much as 50 percent of current water quality degradation in the United States, and as much as 70 percent in the Southeast. In this study, I used an ecological risk assessment methodology, at the watershed scale and riparian scales (zones 300, 100, and 50 feet on either side of streams), to analyze and quantify the impact of nonpoint pollution on the ecological integrity and water quality of North Carolina streams. Specifically, I determined how land-use patterns relate to aquatic ecological integrity, including the extent to which one of the most widely promoted best management practices (BMPs) – the preservation of riparian vegetated buffers – correlates with better ecological integrity. The central goal of this project was the creation of a set of empirical models that describe the vulnerability of North Carolina aquatic ecological integrity – as measured by benthic macroinvertebrate community structure - to changes in the landscape-scale sources of nonpoint pollution. The models, the result of multiple regression analysis of Geographic Information System (GIS)-derived data, take into account watershed eight land form characteristics, and three land cover types derived from 1992 Multi-Resolution Land Characterization (MRLC) Consortium raster data: forest, urban, and agriculture. The land form characteristics considered in this analysis are topographic complexity, mean elevation, watershed slope/relief ratio, watershed area, watershed shape, rainfall, soil clay content, and ecoregion. The regression equation models created by this process can be used by managers and policymakers to weigh the risks of management and policy decisions for a given watershed or set of watersheds, including whether vegetated riparian buffers are ecologically effective and economically efficient in achieving water quality standards. The coefficient of multiple determination (R²) for each equation indicates the proportion of variability in the invertebrate tolerance indices attributable to the landscape variables included in the model. The unstandardized regression coefficients for each landscape variable represent that variable's weight and direction in the vulnerability index equation. The standardized (beta weight) regression coefficients indicate the relative importance of the landscape characteristic relative to the other landscape variables in the model equation. The results of this study indicate that (1) landscape characteristics at the watershed scale predict variability in benthic macroinvertebrate community structure better than characteristics at the riparian scale; (2) land cover variables are of secondary importance to certain land form features, but are still significant predictors of macroinvertebrate community structure; (3) developed land use is the most important land cover variable at the watershed scale, while forested land cover is the most important at the riparian scale; (4) wider riparian buffer zones yield only minor differences in invertebrate community structure; and (5) more research is needed on how these interactions vary by the size of a watershed and the ecoregion in which it is located. Based on these findings, it appears that water quality and stream ecological integrity may be most at risk in North Carolina watersheds where a higher amount of urban development is occurring at the watershed scale, where a lower percentage of forest cover exists in riparian corridors, and where the topography is generally flatter. The ecological risk assessment process that produced these results was relatively simple and inexpensive. The results are straightforward and generally easy to interpret. The vulnerability model equations that resulted from this assessment process can provide a basis for quantitatively comparing, ranking, and prioritizing risks, which can be useful in cost-benefit and cost-effectiveness analyses of alternative management options. Specifically, they offer a useful approach for characterizing the risk of potential land management options through the simulation of land use change, such as conversion of land cover or implementation of best management practices.
Date: 2002-10-16
Degree: MS
Discipline: Natural Resources

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