USGS Scientific Investigations Report 2006-5101-B

Physical, Chemical, and Biological Responses of Streams to Increasing Watershed Urbanization in the Piedmont Ecoregion of Georgia and Alabama, 2003

By M. Brian Gregory and Daniel L. Calhoun

U.S. Geological Survey Scientific Investigations Report 2006-5101-B; 104 pages (Published December 2007)
Chapter B of Effects of Urbanization on Stream Ecosystems in Six Metropolitan Areas of the United States

This report is available in PDF format. On a PC, right click on the PDF link and select "Save Link As"; on a Mac, control click the link and select "Save Link Target As".  Main report (6 Mb)


As part of the U.S. Geological Survey National Water-Quality Assessment Program’s effort to assess the physical, chemical, and biological responses of streams to urbanization, 30 wadable streams were sampled near Atlanta, Ga., during 2002–2003. Watersheds were selected to minimize natural factors such as geology, altitude, and climate while representing a range of urban development. A multimetric urban intensity index was calculated using watershed land use, land cover, infrastructure, and socioeconomic variables that are highly correlated with population density. The index was used to select sites along a gradient from low to high urban intensity. Response variables measured include stream hydrology and water temperature, instream habitat, field properties (pH, conductivity, dissolved oxygen, turbidity), nutrients, pesticides, suspended sediment, sulfate, chloride, Escherichia coli (E. coli) concentrations, and characterization of algal, invertebrate and fish communities. In addition, semipermeablemembrane devices (SPMDs)—passive samplers that concentrate hydrophobic organic contaminants such as polycyclicaromatic hydrocarbons (PAHs)—were used to evaluate water-quality conditions during the 4 weeks prior to biological sampling. Changes in physical, chemical, and biological conditions were evaluated using both nonparametric correlation analysis and nonmetric multidimensional scaling (MDS) ordinations and associated comparisons of dataset similarity matrices.

Many of the commonly reported effects of watershed urbanization on streams were observed in this study, such as altered hydrology and increases in some chemical constituent levels. Analysis of water-chemistry data showed that specific conductance, chloride, sulfate, and pesticides increased as urbanization increased. Nutrient concentrations were not directly correlated to increases in development, but were inversely correlated to percent forest in the watershed. Analyses of SPMD-derived data showed that bioassays and certain chemical constituents such as pyrene and benzophenanthrene, both PAHs found in coal tar, were strongly correlated with measures of watershed urbanization. Hydrologic variability metrics indicated that as urban development increased, streams became flashier, with characteristic high flows having shorter duration. The hydrologic effects associated with urbanization were greatest during the fall and least apparent during the winter. No correlations were observed between increasing urbanization and stream temperature or changes in stream habitat.

Algal, invertebrate, and fish communities exhibited statistically significant changes as watersheds became increasingly urban, with the strongest responses observed in the invertebrate community followed by fishes, then algal diatom communities. Invertebrate communities were the most responsive to increasing urbanization with Ephemeroptera, Plecoptera, and Tricoptera taxa, especially Plecoptera (stoneflies) responding negatively and most strongly to increasing urbanization. Invertebrate communities were influenced more significantly by water quality, although significant responses to altered hydrology also were noted. In terms of the fish community, the percentage of cyprinids present in the stream was the only Index of Biotic Integrity metric that responded negatively to increases in watershed urbanization. Fish community response to urbanization was intermediate relative to algae and invertebrates with respect to significant metric responses as well as the overall community response to increasing urbanization. Measures of hydrologic variability were the most influential environmental variables affecting the algal community.

Although sites were originally chosen to represent a gradient of increasing urbanization, a cluster analysis performed on the component metrics of the urban index categorized sites into four distinct groups. Multivariate analysis based on nonmetric MDS and related analyses of data matrices indicated varying degrees of significant separation of algal, invertebrate, and fish communities from corresponding groups of sites. Pair-wise analysis of similarity of communities among these groups indicated progressive separation (more differences based on species compositions) as sites transitioned from rural, to suburban, to highly developed. Invertebrates and fish communities showed a greater range in community separation than did algal communities. Dispersion, a measure of community variability, decreased as sites became more urbanized, with the least developed group having higher dispersion indices (more different species) and the most developed sites having lower dispersion indices (fewer species) for algal, invertebrate, and fish assemblages. In general, algal, invertebrate, and fish communities in highly urbanized areas are more similar to each other than the communities are to each other in the least developed areas.




Purpose and Scope

Study Area

Land-Use History


Site Selection

Network Design

Data Collection and Processing

Water Quality


Water Temperature

Stream Habitat

Algal Communities

Invertebrate Communities

Fish Communities

Statistical Analysis

Correlation Analysis

Multivariate Community Analysis

Physical, Chemical, and Biological Responses to Urbanization

Water-Quality Response

Hydrologic Response

Temperature Response

Algal Metric Responses

Invertebrate Metric Responses

Fish-Metric Responses

Algal Community Responses

Invertebrate Community Responses

Fish Community Responses

Summary and Conclusions

References Cited

Appendix A. GIS Variable Names, Abbreviations, and Descriptions

Appendix B. Chemical Variable Names and Descriptions

Appendix C. Physical Variable Names and Descriptions

Appendix D. Biological Variable Names and Descriptions

Appendix E. Species Lists for Algal, Invertebrate, and Fish Communities



Suggested citation:

Gregory, M.B., and Calhoun, D.L., 2007, Physical, chemical, and biological responses of streams to increasing watershed urbanization in the Piedmont Ecoregion of Georgia and Alabama, Chapter B of Effects of urbanization on stream ecosystems in six metropolitan areas of the United States: U.S. Geological Survey Scientific Investigations Report 2006–5101-B, 104 p., available online only at

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