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Temporal Analyses of Select Macroinvertebrates in the Upper Mississippi River System, 1992-1995.
GEOLOGICAL SURVEY ONALASKA WI ENVIRONMENTAL MANAGEMENT TECHNICAL CENTER
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The annual variability in mayflies Ephemeroptera, fingernail clams Sphaeriidae, and midges chironomidae in six study areas of the Upper Mississippi River System from 1992 to 1995 was examined. Spatial distribution is also discussed for these organisms along with the Asiatic clam Corbicuta Fluminea and the zebra mussel Dreissena polymorpha. Sample allocation within each reach was based on a stratified random design where strata were aquatic areas. No significant linear trends across years were found in estimated reachwide mean number of organisms. However, the overall test for differences in intercepts among study areas was statistically significant P 0.05 for mayflies, fingernail clams, and midges. No statistical difference in trend slopes among reaches were detected. In 1993, the estimated mean density of fingernail clams in Pool 13 was 35 times that found in other study areas. Overall, impounded aquatic areas and silt clay substrates supported higher numbers of the select macroinvertebrates.
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