RELATIONS OF FISH COMMUNITY COMPOSITION TO ENVIRONMENTAL VARIABLES INSTREAMS OF CENTRAL NEBRASKA, USA

Nine sites on streams in the Platte River Basin in central Nebraska we re sampled as part of the US Geological Survey's National Water-Qualit y Assessment Program during 1993-1994. A combination of canonical corr espondence analysis and an index of biotic integrity determined from f ish community data produced complementary evaluations of water-quality conditions. Results of the canonical correspondence analysis were use ful in showing which environmental variables were significant in diffe rentiating fish communities at the nine sites. Five environmental vari ables were statistically significant in the analysis. Median specific conductance of water samples collected at a site accounted for the lar gest amount of variability in the species data. Although the percentag e of the basin as cropland was not the first variable chosen ina forwa rd selection process, it was the most strongly correlated with the fir st ordination axis. A rangeland-dominated site was distinguished from all others along that axis. Median orthophosphate concentration of sam ples collected in the year up to the time of fish sampling was most st rongly correlated with the second ordination axis. The index of biotic integrity produced results that could be interpreted in terms of the relative water quality between sites. Sites draining nearly 100% cropl and had the lowest scores for two individual metrics of the index of b iotic integrity that were related to species tolerance. Effective moni toring of water quality could be achieved by coupling methods that add ress both the ecological components of fish communities and their stat istical relationships to environmental factors.