Comparison of Macroinvertebrate‐Derived Stream Quality Metrics Between Snag and Riffle Habitats1 |
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| Authors: | Kristine F Stepenuck Ronald L Crunkilton Michael A Bozek Lizhu Wang |
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| Institution: | 1. Respectively, Graduate Student, Wisconsin Cooperative Fishery Research Unit, U.S. Geological Survey, College of Natural Resources, University of Wisconsin–Stevens Point at the time this paper was prepared, now Volunteer Stream Monitoring Program Coordinator, University of Wisconsin‐Extension and Wisconsin Department of Natural Resources, 445 Henry Mall, Room 202, Madison, Wisconsin 53706;2. Professor, College of Natural Resources, University of Wisconsin–Stevens Point;3. Unit Leader, Wisconsin Cooperative Fishery Research Unit, USGS, College of Natural Resources, University of Wisconsin–Stevens Point;4. Research Scientist, Wisconsin Department of Natural Resources, Bureau of Science Services at the time this article was prepared, now Director, Institute for Fisheries Research, Michigan Department of Natural Resources, University of Michigan, Ann Arbor, Michigan 48109. |
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| Abstract: | Abstract: We compared benthic macroinvertebrate assemblage structure at snag and riffle habitats in 43 Wisconsin streams across a range of watershed urbanization using a variety of stream quality metrics. Discriminant analysis indicated that dominant taxa at riffles and snags differed; Hydropsychid caddisflies (Hydropsyche betteni and Cheumatopsyche spp.) and elmid beetles (Optioservus spp. and Stenemlis spp.) typified riffles, whereas isopods (Asellus intermedius) and amphipods (Hyalella azteca and Gammarus pseudolimnaeus) predominated in snags. Analysis of covariance indicated that samples from snag and riffle habitats differed significantly in their response to the urbanization gradient for the Hilsenhoff biotic index (BI), Shannon’s diversity index, and percent of filterers, shredders, and pollution intolerant Ephemeroptera, Plecoptera, and Trichoptera (EPT) at each stream site (p ≤ 0.10). These differences suggest that although macroinvertebrate assemblages present in either habitat type are sensitive to detecting the effects of urbanization, metrics derived from different habitats should not be intermixed when assessing stream quality through biomonitoring. This can be a limitation to resource managers who wish to compare water quality among streams where the same habitat type is not available at all stream locations, or where a specific habitat type (i.e., a riffle) is required to determine a metric value (i.e., BI). To account for differences in stream quality at sites lacking riffle habitat, snag‐derived metric values can be adjusted based on those obtained from riffles that have been exposed to the same level of urbanization. Comparison of nonlinear regression equations that related stream quality metric values from the two habitat types to percent watershed urbanization indicated that snag habitats had on average 30.2 fewer percent EPT individuals, a lower diversity index value than riffles, and a BI value of 0.29 greater than riffles. |
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| Keywords: | land use macroinvertebrate community assemblages streams riffles snags urbanization discriminant analysis imperviousness |
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