We analyzed the relation of the amount and spatial pattern of land cover with stream fish communities, in-stream habitat, and baseflow in 47 small southeastern Wisconsin, USA, watersheds encompassing a gradient of predominantly agricultural to predominantly urban land uses. The amount of connected impervious surface in the watershed was the best measure of urbanization for predicting fish density, species richness, diversity, and index of biotic integrity (IBI) score; bank erosion; and base flow. However, connected imperviousness was not significantly correlated with overall habitat quality for fish. Nonlinear models were developed using quantile regression to predict the maximum possible number of fish species, IBI score, and base flow for a given level of imperviousness. At watershed connected imperviousness levels less than about 8%, all three variables could have high values, whereas at connected imperviousness levels greater than 12% their values were inevitably low. Connected imperviousness levels between 8 and 12% represented a threshold region where minor changes in urbanization could result in major changes in stream condition. In a spatial analysis, connected imperviousness within a 50-m buffer along the stream or within a 1.6-km radius upstream of the sampling site had more influence on stream fish and base flow than did comparable amounts of imperviousness further away. Our results suggest that urban development that minimizes amount of connected impervious surface and establishes undeveloped buffer areas along streams should have less impact than conventional types of development.

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We analyzed data from 79 watersheds in an undegraded U.S. ecoregion to identify key environmental factors that explained stream fish assemblage patterns and to evaluate the relative influence of environmental factors operating at different spatial scales. A few key factors from the watershed, reach, and riparian scale explained a significant amount of the variance in fish attributes. Three environment–fish associations were evident. Top carnivores and intolerant cold-water fishes were associated with relatively narrow, deep, high-gradient, cold streams with strong groundwater inputs. Tolerant cyprinids occurred in small streams with low groundwater input, low dissolved oxygen, and abundant macrophytes. A diverse assemblage (Cyprinidae, Catostomidae, Centrarchidae, Percidae) existed in warm, wide streams in watersheds dominated by lacustrine sand and gravel geology and abundant wetlands and lakes. Overall, reach-scale variables directly explained the most, watershed-scale variables less, and riparian-scale variables the least variation in fish attributes. Watershed and riparian variables had indirect connections with fishes through their direct influence on reach variables. In conjunction with findings from more degraded regions, we conclude that the relative influence of reach-scale variables on fishes are greatest in undegraded areas and that direct effects of watershed-scale variables are increasingly important as human modifications of the landscape increase.

The index of biotic integrity (IBI). developed from information on the structure, composition, and functional organization of fish assemblages, is used to assess the health of aquatic ecosystems. We analyzed two large statewide data sets on stream fish assemblages to develop and test a version of the IBI for application to Wisconsin coldwater streams (maximum daily mean water temperature usually <22°C). This new IBI is needed because fish assemblages in Wisconsin coldwater streams differ significantly from those in warmwater streams (maximum daily mean temperature >24°C), for which an IBI already exists. High‐quality coldwater streams have few species, with salmonids and cottids dominating. and lack many of the taxonomic groups that are important in high‐quality warmwater streams. In contrast, high‐quality warmwater streams have numerous species, and cyprinids, catostomids, centrarchids, and percids typically dominate. Environmental degradation often causes an increase in species richness in coldwater fish assemblages, the opposite of what occurs in warmwater assemblages, as a small number of coldwater species are replaced by a larger number of more tolerant eurythermal and warmwater species. The new coldwater IBI has five metrics: (1) number of intolerant species, (2) percent of all individuals that are tolerant species, (3) percent of all individuals that are top carnivore species, (4) percent of all individuals that are native or exotic stenothermal coldwater or coolwater species, and (5) percent of salmonid individuals that are brook trout Salvelinus fontinalis. No regional or stream‐size adjustments in metric scoring criteria are needed. Relative coldwater IBI scores and ratings of stream sites throughout Wisconsin closely match independent rankings of environmental quality on the basis of physical habitat and water quality of the sites. Variation in IBI scores within and among years is gencrally low. The new coldwater IBI is not appropriate for coolwater streams (typical maximum summer daily mean temperature 22–24°C).

We compared watershed land‐use and fish community data between the 1970s and 1990s in 47 small streams in southeastern Wisconsin. Our goal was to quantify effects of increasing urbanization on stream fishes in what had been a predominantly agricultural region. In the 43 test watersheds, mean surface coverage by agricultural lands decreased from 54 percent to 43 percent and urban lands increased from 24 percent to 31 percent between 1970 and 1990. Agriculture dominated the four reference watersheds, but neither agriculture (65–59 percent) nor urban (4.4–4.8 percent) land‐uses changed significantly in those watersheds during the study period. From the 1970s to the 1990s the mean number of fish species for the test stream sites decreased 15 percent, fish density decreased 41 percent, and the index of biotic integrity (IBI) score dropped 32 percent. Fish community attributes at the four reference sites did not change significantly during the same period, although density was substantially lower in the 1990s. For both the 1970s and 1990s test sites, numbers of fish species and IBI scores were positively correlated with watershed percent agricultural land coverage and negatively correlated with watershed urban land uses, as indexed by percent effective connected imperviousness. Numbers of fish species per site and IBI scores were highly variable below 10 percent imperviousness, but consistently low above 10 percent. Sites that had less than 10 percent imperviousness and fewer than 10 fish species in the 1970s suffered the greatest relative increase in imperviousness and decline in species number over the study period. Our findings are consistent with previous studies that have found strong negative effects of urban land uses on stream ecosystems and a threshold of environmental damage at about 10 percent imperviousness. We conclude that although agricultural land uses often degrade stream fish communities, agricultural land impacts are generally less severe than those from urbanization on a per‐unit‐area basis.

We used temperature and fish data from streams across Michigan and Wisconsin to estimate upper thermal tolerance limits for brook trout Salvelinus fontinalis and brown trout Salmo trutta. Tolerance limits were estimated for the maximum daily mean temperature (MEANT), maximum daily maximum temperature (MAXT), and maximum daily temperature range (RNGT) at exposure lengths of 1, 3, 7, 14, 21, 28, 35, 42, 49, 56, and 63 d. We found no difference in the upper thermal tolerance limit for brook and brown trout. For time periods of 1-14 d, the upper temperatures tolerated by trout decreased rapidly from 25.38C to 22.58C for MEANT and from 27.68C to 24.68C for MAXT. For time periods from 21 to 63 d, the upper temperatures tolerated by trout declined more gradually from 22.18C to 21.08C for MEANT and from 24.28C to 22.98C for MAXT. The 7-d upper tolerance limit was 23.38C for MEANT and 25.48C for MAXT. The maximum RNGT tolerated by trout varied as a function of mean temperature and length of exposure. Our findings suggest that chronic temperature effects as well as temperature fluctuation play an important role in limiting salmonid distributions and therefore should be considered when developing management objectives and water quality standards.

We sampled 240 wadeable streams across Wisconsin for different forms of phosphorus and nitrogen, and assemblages of macroinvertebrates and fish to (1) examine how macroinvertebrate and fish measures correlated with the nutrients; (2) quantify relationships between key biological measures and nutrient forms to identify potential threshold levels of nutrients to support nutrient criteria development; and (3) evaluate the importance of nutrients in influencing biological assemblages relative to other physicochemical factors at different spatial scales. Twenty-three of the 35 fish and 18 of the 26 macroinvertebrate measures significantly correlated (P < 0.05) with at least one nutrient measure. Percentages of carnivorous, intolerant, and omnivorous fishes, index of biotic integrity, and salmonid abundance were fish measures correlated with the most nutrient measures and had the highest correlation coefficients. Percentages of Ephemeroptera-Plecoptera-Trichoptera individuals and taxa, Hilsenhoff biotic index, and mean tolerance value were macroinvertebrate measures that most strongly correlated with the most nutrient measures. Selected biological measures showed clear trends toward degradation as concentrations of phosphorus and nitrogen increased, and some measures showed clear thresholds where biological measures changed drastically with small changes in nutrient concentrations. Our selected environmental factors explained 54% of the variation in the fish assemblages. Of this explained variance, 46% was attributed to catchment and instream habitat, 15% to nutrients, 3% to other water quality measures, and 36% to the interactions among all the environmental variables. Selected environmental factors explained 53% of the variation in macroinvertebrate assemblages. Of this explained variance, 42% was attributed to catchment and instream habitat, 22% to nutrients, 5% to other water quality measures, and 32% to the interactions among all the environmental variables.

Macroinvertebrates were used to assess the impact of urbanization on stream quality across a gradient of watershed imperviousness in 43 southeastern Wisconsin streams. The percentage of watershed connected imperviousness was chosen as the urbanization indicator to examine impact of urban land uses on macroinvertebrate communities. Most urban land uses were negatively correlated with the Shannon diversity index, percent of pollution intolerant Ephemeroptera, Plecoptera, and Trichoptera individuals, and generic richness. Nonurban land uses were positively correlated with these same metrics. The Hilsenhoff biotic index indicated that stream quality declined with increased urbanization. Functional feeding group metrics varied across a gradient of urbanization, suggesting changes in stream quality. Proportions of collectors and gatherers increased, while proportions of filterers, scrapers, and shredders decreased with increased watershed imperviousness. This study demonstrated that urbanization severely degraded stream macroinvertebrate communities, hence stream quality. Good stream quality existed where imperviousness was less than 8 percent, but less favorable assessments were inevitable where imperviousness exceeded 12 to 20 percent. Levels of imperviousness between 8 and 12 percent represented a threshold where minor increases in urbanization were associated with sharp declines in stream quality. (KEY TERMS: aquatic ecosystems; nonpoint source pollution; urban landuse; imperviousness; urban runoff; stream quality; macroinvertebrates; biotic index; functional feeding groups.)