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.)

Abstract-Increasing concentrations of nitrate in surface water and groundwater are becoming a worldwide concern, yet little information has been published on toxicity of nitrate to common organisms used for toxicity testing. The acute and chronic toxicity of nitrate to Ceriodaphnia dubia, Daphnia magna, and Pimephales promelas was investigated in 48-h to 17-d laboratory exposures. The 48-h median lethal concentration (LC50) of nitrate to C. dubia and D. magna neonates was 374 mg/L NO 3 -N and 462 mg/L NO 3 -N. The no-observed-effect concentration (NOEC) and the lowest-observed-effect concentration (LOEC) for neonate production in C. dubia were 21.3 and 42.6 mg/L NO 3 -N, respectively. The NOEC and LOEC values for neonate production in D. magna were 358 and 717 mg/L NO 3 -N, respectively. The 96-h LC50 for larval fathead minnows (P. promelas) was 1,341 mg/L NO 3 -N. The NOEC and LOEC for 7-d larval and 11-d embryo-larval growth tests were 358 and 717 mg/L NO 3 -N, respectively. Additional exposure of breeding P. promelas and their fertilized eggs to nitrate did not increase susceptibility further. The LC50 values for all species tested were above ambient concentrations of nitrate reported for surface water. However, the LOEC for C. dubia was within the range of concentrations that could be found in streams draining areas under extensive agricultural cultivation.

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