Fish communities and their relation to environmental factors in the eastern Iowa basins in Iowa and Minnesota, 1996

Fish community data were collected by the U.S. Geological Survey (USGS) at 12 sites in 1996 in the Wapsipinicon, the Cedar, the Iowa, and the Skunk River Basins in eastern Iowa. The study was done as part of the National Water-Quality Assessment (NAWQA) Program of the USGS. This report presents an evaluation of the fish communities, the composition and conditions of the fish communities,and by relating these compositions and conditions to a variety of habitat and water-quality factors.

A total of 56 fish species representing 13 families were collected from among the 12 sites in 1996. The family with the most species represented were the minnows with 20. The number of individuals of all species collected in one sampling pass ranged from 472 at the Iowa River near Rowan to 2,072 at Wolf Creek near Dysart. Fish community composition was similar among many of the stream sites. The fish community at 4 of the 5 stream sites, as well as at 2 of the large-river sites, was similar to the reference site, the Wapsinicon River near Tripoli, an indication that fish communities across the study unit are similar. The sites that were the least similar to any of the other sites include Flood Creek, a stream site, and the Skunk River at Augusta large-river site. The fish communities at both of these sites were dominated by relatively few species, many of which are tolerant or represent degraded environmental conditions.

Biplots of detrended correspondence analysis ordinations indicate a gradient from the stream sites to the large-river sites. The detrended correspondence analysis ordination also indicates that the stream sites are more closely clustered than the large-river sites. The large-river sites were more likely to have their ordination driven by one or two dominant species, while several species occurred in similar relative abundance at many of the stream sites.

Several indexes of biotic integrity (IBI) based on fish community were applied to the data
and results were generally comparable. In general, the IBIs indicate higher biotic integrity at the stream sites than the large-river sites. Based on IBI classifications, fish communities at most sites were degraded compared to reference conditions. The fish communities at the 12 study sites appear to be related to a number of environmental factors. Obvious differences in fish communities occur between the stream sites and the large-river sites, the result of differences in both physical and chemical characteristics of the streams. Important physical factors related to fish communities included several directly related to stream size as well as human population density and percent of rowcrops in the watershed. Chemical factors that were important included median total phosphorus, suspended-sediment, and dissolved organic carbon concentrations.