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This study describes the benthic invertebrate communities of 20 benchmark streams in agricultural areas of eastern Wisconsin. Streams with minimal adverse effects from human activity were selected from four agricultural areas with differing surficial deposits and bedrock types (relatively homogeneous units, or RHU's). Most aquatic invertebrate orders were well represented in the 20 benchmark stream samples; 217 species and 151 genera within 56 families were identified. Diptera was the best represented order (96 species), followed by Trichoptera (42 species) and Ephemeroptera (26 species). Diptera were the most abundant organisms in terms of numbers of individuals in the sample (28 percent of the total) followed by Trichoptera (25 percent) and Ephemeroptera (13 percent). Nine species of freshwater mussels were found, but only in 5 of the 20 benchmark streams. Community measures were calculated for the following: total number of individuals; number of species; number of families; Margalef's diversity index; percent dominant family; percent Ephemeroptera-Plecoptera-Trichoptera (EPT); ratio of EPT to Chironomidae; percent shredders; ratio of scrapers to collectors-gatherers-filterers; Hilsenhoff's Biotic Index; Hilsenhoff's family level biotic index; and mean tolerance value. The S AS statistical software package was used for calculations of variance and correlations, normality checks, and principal components analysis of these measures and to find relations between benthic-invertebrate data and environmental-setting, habitat, and water-quality data. Coefficients of variation within the RHU's were as great or greater than those for all 20 streams for most measures and RHU's. The specific taxa assemblages present at the sites did not show distinct differences between RHU's or similarities within the RHU's. The covariance and the Kruskal-Wallis tests showed that the benthic invertebrate measures were not related to RHU. These results all indicate that the combined effect of the RHU variables (bedrock geology, texture of surficial deposits, and land use/land cover) were not elemental in describing invertebrate communities in the study-area streams. A principal components analysis (PCA) was done on the 20 benchmark streams which used the invertebrate population measures as variables. A three-dimensional ordination plot of these components revealed that 18 of the 20 streams could be divided into three groups relative to stream size, available habitat, and water quality. The three classifications of streams include large, warmer streams with slight pollution; deep, mixed-water streams with minimal pollution; and small, cold, pristine headwater streams. The two streams not defined by the three PCA groupings were not suitable to represent benchmark conditions. One site lacked suitable quality habitat or sufficient nutrients to support a healthy population of invertebrates, causing low Abstract 1 measures of diversity. The other site appeared to be affected by sedimentation and low flows. The classification groupings did not show any significant relations to percentage agricultural land use. Percentage of agricultural land use varied greatly within each group and the means for each group were similar. All streams in this study had some level of protection from agricultural practices in their basins. Although the intensity of agriculture is known to be a factor causing deterioration of invertebrate populations in past studies, the finding in this study indicated that the level of protection the stream received and other factors such as environmental setting and habitat could be more important to benthic invertebrates than the percentage of agriculture in the basin. Information gathered from these benchmark streams can be used as a regional reference for comparison with other streams in agricultural areas, based on communities of aquatic biota, habitat, and water quality. INTRODUCTION In 1991, the U.S. Geological Survey (USGS) began implementation of the National Water-Quality Assessment (NAWQA) Program. The objectives of the NAWQA Program are to (1) describe current water-quality conditions for a large part of the Nation's freshwater streams, rivers, and aquifers, (2) describe trends in water quality over time, and (3) improve understanding of the primary natural and human factors that affect water-quality conditions. This information will be useful for planning future management actions and examining their likely consequences. In all, 60 study units are planned to begin activities on a staggered time scale (Leahy and others, 1990). The Western Lake Michigan Drainages study unit was selected as one of the first 20 study units and began data collection and analysis in 1991. The effects of agriculture on stream biota is an important issue in the study unit. The introduction of sediments, organic matter, nutrients, and toxic substances such as pesticides into a stream and the effects of channelization and habitat loss may cause deterioration of water quality in agricultural areas (Pajak and others, 1994). Although numerous studies of the aquatic biota and habitat of agriculturally affected streams have been done in the Western Lake Michigan Drainages, very few studies focused on defining the composition of healthy stream communities; that is, those with limited adverse anthropogenic effects. In order for scientists and water-resources managers to measure the effects of changes in agricultural practices on stream communities or the extent of degradation at affected sites, biological communities of healthy streams need to be identified to provide benchmarks against which comparisons can be made. In response to this need, the Western Lake Michigan Drainages study unit team identified 20 minimally affected stream sites to serve as benchmarks for subsequent studies of aquatic communities. Purpose and Scope This report provides information on the benthic invertebrate communities of 20 benchmark streams in agricultural areas of eastern Wisconsin. Environmental characteristics of bedrock geology, texture of surficial deposits, and land use/land cover that are believed to influence water quality in the WMIC study unit were used to subdivided the study unit into 28 relatively homogeneous units (RHU's) (Robertson and Saad, 1996). The 20 benchmark streams sampled are in four of the largest RHU's in the study unit (1,3, 20, and 26) (Robertson and Saad, 1996). The four RHU's have primarily agricultural land use and differing bedrock and surficial geology. The benchmark streams were sampled for this study from May 1993 through July 1995. The distribution, relative abundance, and community structure of the benthic invertebrates of these streams are discussed based upon samples collected at specific stream reaches described in the environmental settings report by Rheaume and others (1996). Information is provided for macroinvertebrate communities including richness measures, enumeration, functional feeding groups, and biotic indices of these invertebrate populations. Summaries of sampling gear and techniques, sample-identification procedures, and usefulness of various benthic invertebrate measures are included in this report. Effects of environmental setting, habitat, and water quality on benthic invertebrate communities are discussed. The 20 streams are classified into groups and their suitability as benchmark sites for invertebrate communities are discussed. Benthic Invertebrates of Benchmark Streams in Agricultural Areas of Eastern Wisconsin Western Lake Michigan Drainages The benthic-invertebrate information included in this report represents only part of the biotic information collected at these streams in the Western Lake Michigan Drainages study unit of the NAWQA Program. Other information collected to define benchmark streams in agricultural areas include environmental settings, habitat, and the algal and fish communities at these sites. Western Lake Michigan Drainages Study Unit The Western Lake Michigan Drainages study unit encompasses a 51,541 km2 area in eastern Wisconsin and the Upper Peninsula of Michigan (fig. 1, inset map). Ten major rivers drain the study unit: the Escanaba and Ford Rivers in Michigan; the Menominee River, which partially defines the state boundary between Wisconsin and Michigan; the Peshtigo and Oconto Rivers in northeastern Wisconsin; the Fox/ Wolf River complex in east-central Wisconsin, which drains into Green Bay; and the Manitowoc, Sheboygan, and Milwaukee Rivers, which drain the southeastern part of the study unit. The overall population in the study unit is 2,435,000 (U.S. Bureau of Census, 1991). The major cities and their populations are Milwaukee, 628,000; Green Bay, 96,000; Racine, 84,000; Kenosha, 80,000; and Appleton, 66,000. Agriculture is the major land use, with 37 percent of the study unit devoted to cropland and 6 percent to pasture. About 40 percent of the study unit, predominantly the northwestern part, is forested; here streams and lakes offer excellent opportunities for fishing, boating, and other recreation. Lake Winnebago, a 555,442-hectare lake in the Fox River Basin, is a major surface-water feature of the study unit. Study Design The 20 benchmark streams sampled are in four of the largest RHU's in the study unit (1,3, 20, and 26) (fig. 1). RHU 1 (clayey surficial deposits over carbonate bedrock) and RHU 3 (sandy-till surficial deposits over carbonate bedrock) are in adjacent agricultural areas in the Southeastern Wisconsin Till Plains ecoregion. RHU 20 (sandy surficial deposits over igneous and metamorphic bedrock) and RHU 26 (sandy surficial deposits over sandstone bedrock) are in adjacent areas of agriculture and mixed forests in the North Central Hardwood Forests ecoregion (Omernik and Gallant, 1988). Twenty benchmark streams in these four RHU's were selected for sampling (table 1). RHU and landscape classifications, regional ecological patterns, land-cover and land-use informat

Benthic invertebrates of benchmark streams in agricultural areas of eastern Wisconsin — Western Lake Michigan drainages