|
||||
Scientific Investigations Report 2006-5101-A |
Effects of Urbanization of Stream Ecosystems in the South Platte River Basin, Colorado and WyomingBy Lori A. Sprague, Robert E. Zuellig, and Jean A. DupreeThis document also is available in pdf format:
SIR2006-5101-A (4.03 MB)--ONLINE
ONLY The citation for this report, in USGS format, is as follows:
AbstractThis report describes the effects of urbanization on physical, chemical, and biological characteristics of stream ecosystems in 28 basins along an urban land-use gradient in the South Platte River Basin, Colorado and Wyoming, from 2002 through 2003. Study basins were chosen to minimize natural variability among basins due to factors such as geology, elevation, and climate and to maximize coverage of different stages of urban development among basins. Because land use or population density alone often are not a complete measure of urbanization, land use, land cover, infrastructure, and socioeconomic variables were integrated in a multimetric urban intensity index to represent the degree of urban development in each study basin. Physical characteristics studied included stream hydrology, stream temperature, and habitat; chemical characteristics studied included nutrients, pesticides, suspended sediment, sulfate, chloride, and fecal bacteria concentrations; and biological characteristics studied included algae, fish, and invertebrate communities. Semipermeable membrane devices (SPMDs), passive samplers that concentrate trace levels of hydrophobic organic contaminants like polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), also were used. The objectives of the study were to (1) examine physical, chemical, and biological responses along the gradient of urbanization; (2) determine the major physical, chemical, and landscape variables affecting the structure of aquatic communities; and (3) evaluate the relevance of the results to the management of water resources in the South Platte River Basin. Commonly observed effects of urbanization on instream physical, chemical, and biological characteristics, such as increased flashiness, higher magnitude and more frequent peak flows, increased concentrations of chemicals, and changes in aquatic community structure, generally were not observed in this study. None of the hydrologic, temperature, habitat, or chemical variables were correlated strongly (Spearman’s rho greater than or equal to 0.7) with urban intensity, with the exception of some of the SPMD-based toxicity and chemical variables. SPMD-based measures of potential toxicity and PAH concentrations were positively correlated with urban intensity. The PAH concentrations also were positively correlated with measures of road density and negatively correlated with distance to the nearest road, indicating that automobile exhaust is a major source of these compounds in the study area. This source may be localized enough that the transport of PAHs would be minimally affected by water-management practices such as diversion or storage upstream. In contrast, the predominant sources of nutrients, bacteria, suspended sediment, sulfate, chloride, and pesticides may be more dispersed throughout the drainage area and, therefore, their transport to downstream sites may be subject to greater disruption by water regulation. Although no direct link was found between most water-chemistry characteristics and urbanization, invertebrate, algae, and fish-community characteristics were strongly associated with nutrients, pesticides, sulfate, chloride, and suspended sediment. None of the biological community variables were strongly correlated with the urban intensity index. Algal biomass predominantly was associated with total nitrogen concentrations, nitrite-plus-nitrate concentrations, and the duration of high flows. Fish communities predominantly were associated with housing age, the percentage of suspended sediment finer than 0.063 millimeters and chloride concentrations. Invertebrate communities predominantly were associated with the frequency of rising and falling flow events, the duration of high flows, total nitrogen concentrations, nitrite-plus-nitrate concentrations, and total herbicide concentrations. Historical records indicate that aquatic communities in the region may have been altered prior to any substantial urban development by early agricultural and water-management practices. Present-day aquatic communities are composed primarily of tolerant species even in areas of minimal urban development; when development does occur, the communities already may be resistant to disturbance. In addition to the effects of historical stressors on aquatic community structure, it is possible that current water-management practices in the study basins are having an effect. In the absence of natural, unaltered hydrologic conditions, more sensitive taxa may be unable to recolonize urban streams. The movement and storage of water also may lead to a disconnect between the land surface and streams, resulting in instream physical, chemical, and biological characteristics that, to some degree, are independent of land-cover characteristics. Table of ContentsAbstract Introduction Purpose and Scope Study Area Acknowledgments Approach Site Selection Variability in Natural Landscape Features Gradient in the Degree of Urbanization Suitability of Local Site Conditions Data Collection Physical Characteristics Stream Hydrology Stream Temperature Habitat Chemical Characteristics Biological Characteristics Algae Communities Fish Communities Invertebrate Communities Data Analysis GIS Variables Calculation of the Final Urban Intensity Index Additional GIS Variables Physical Characteristics Stream Hydrology Stream Temperature Habitat Chemical Characteristics Seasonal Variability Spatial Variability Biological Characteristics Resolving Ambiguities Community Summarization Effects of Urbanization on Stream Ecosystems Response of Physical Characteristics Stream Hydrology Stream Temperature Habitat Response of Chemical Characteristics Seasonal Characteristics Spatial Characteristics Water Chemistry SPMD-Based Toxicity and Chemistry Comparison of Water Chemistry and SPMD-Based Toxicity and Chemistry Response of Biological Characteristics Algal communities Algal Response to Urbanization Algal Response to Hydrology and Habitat Algal Response to Water Chemistry Fish Communities Fish Response to Urbanization Fish Response to Hydrology and Habitat Fish Response to Water Chemistry Invertebrate Communities Invertebrate Response to Urbanization Invertebrate Response to Hydrology and Habitat Invertebrate Response to Water Chemistry Major Findings from Response Characteristics Summary and Conclusions References Cited Appendix 1. GIS Variables Appendix 2. Physical Variables Appendix 3. Chemical Variables Appendix 4. Data from Semipermeable Membrane Devices Appendix 5. Biological Variables Appendix 6. Scatterplots of Variables Presented in Report Tables |
AccessibilityFOIAPrivacyPolicies and Notices | |
U.S.
Department of the Interior, U.S.
Geological Survey Persistent URL: http://pubs.water.usgs.gov/sir2006-5101A Page Contact Information: Publications Team Last modified: Wednesday, 26-Jul-2006 10:30:14 EDT |