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Colorado Water Science Center

USING MULTIPLE LINES OF EVIDENCE TO ASSESS WATER QUALITY IN THE SOUTH PLATTE RIVER BASIN

National Water-Quality Assessment (NAWQA) Program
South Platte River Basin Study

by Cathy M. Tate and Janet S. Heiny 1

ABSTRACT

Ecological surveys of invertebrate communities, physical and chemical variables, and contaminants in fish tissue and bed sediment were used to assess water quality in the South Platte River Basin. Invertebrate communities were sampled and physical and chemical measurements were taken basinwide during summer 1992. Ordination of sites based on taxonomic structure of the invertebrate community was done using detrended correspondence analysis, and sites were divided into four groups: mountains, plains/tributary, plains/ braided channel, and plains/ downstream from point source. Differences among site groups were related to physical (gradient, channel width, temperature) and chemical (conductivity, nutrient concentrations) attributes of the sites and their associated land use. The number of taxa was greater in mountain sites (25) compared to all plains sites (<18) and lowest in plains/downstream from point-source sites (11). Whole fish and fine-grained bed sediment were analyzed for organochlorine compounds. Total DDT (T-DDT) and total chlordane (T-Chlor) concentrations were greater in fish tissue (mean = 274 µg/kg T-DDT; 54 µg/kg T-Chlor) than in bed sediment (mean = 5 µg/kg T-DDT; 2 µg/kg T- Chlor) and both varied with land use (T-DDT highest in agriculture; T-Chlor highest in urban). Integration of results from the ecological surveys, physical and chemical variables, and contaminants in fish tissue and bed sediment indicate that water quality is related to land-use practices in the South Platte River Basin.

1 U.S. Geological Survey, Box 25046, MS 415, Denver Federal Center, Lakewood, CO 80225

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