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Relation of Fish Communities to Physical and Chemical Variables at Nine Stream Sites in the Platte River Basin

By Robert B. Swanson and Steven A. Frenzel
ABSTRACT: Species composition of fish communities was related to selected physical and chemical variables at nine sites in the Platte River basin from North Platte, Nebraska downstream to the confluence with the Missouri River near Omaha, Nebraska. The multivariate data included abundances for 36 fish species, characteristics of the nine drainages, site-specific habitat and water-quality characteristics measured during the 1993 water year. Land-use variables were calculated for the entire drainage area at sites draining less than 4,000 km2, and for the lower 4,000 km2 of larger drainages. Canonical correspondence analysis was used to relate environmental characteristics to species data. This method restricts the number of environmental variables to be less than the number of samples. To reduce the number of variables a correlation matrix of 37 variables was examined. Many variables such as concentrations of four herbicides, nutrients, and dissolved organic carbon were highly correlated with each other and with the percentage of the drainage area in cropland. Six variables selected for analysis were: percentage of drainage area in cropland, maximum water temperature, minimum suspended sediment concentration, channel slope, time since a flow of 99 percent exceedance, and the ratio of stream width to depth. These variables explained 64 percent of the variability in species data. Ordination of the fish community data showed that larger river sites which typically had more fish species than smaller sites were grouped together. Two sites draining areas with more than 90 percent cropland were grouped together. Another drainage dominated by cropland was isolated in the ordination. This site had the fewest fish species (4) and lowest total abundance (43). A site in the Nebraska Sandhills, predominantly herbaceous rangeland, also was isolated in the ordination.

Swanson, Robert B., and Frenzel, Steven A., 1994, Relation of fish communities to physical and chemical variables at nine stream sites in the Platte River basin, [abs.], in Sorenson, Stephen K., ed., 1994, Proceedings abstracts American Water Resources Association's symposium on the National Water-Quality Assessment Program--November 7-9, 1994, Chicago, Illinois: U.S. Geological Survey Open-File Report 94-397, p. 19.

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