. Critical trends in Illinois ecosystems. Ecological assessment (Biology); Environmental impact analysis; Nature; Pollution; Conservation of natural resources; Environmental quality. Ecosystem Monitoring Results 33 Table 13- MBI:Mean, Standard Deviation, and Range Mean Standard High Deviation Low 1995 1996 1997 1998 1999 Overall Taxa Dominance: Taxa dominance, calculated for RiverWatch, measures the percentage of the three most common taxa compared to the rest of the sample. Dominance by just a
. Critical trends in Illinois ecosystems. Ecological assessment (Biology); Environmental impact analysis; Nature; Pollution; Conservation of natural resources; Environmental quality. Ecosystem Monitoring Results 33 Table 13- MBI:Mean, Standard Deviation, and Range Mean Standard High Deviation Low 1995 1996 1997 1998 1999 Overall Taxa Dominance: Taxa dominance, calculated for RiverWatch, measures the percentage of the three most common taxa compared to the rest of the sample. Dominance by just a few taxa indicates lower stream quaUt)'. Taxa dominance averaged statewide, with ISIS watershed averages ranging from to Spoon and the Big Muddy/Cache/Saline watersheds had the lowest taxa dominance, demonstrating better health. The Kaskaskia, Little Wabash, and LaMoine showed the biggest problems with taxa dominance, indicating that they were the least healthy. Six taxa are most often associated with taxa dominance in Illinois streams — sowbugs, caddisflies, midges, scuds, black flies and mayflies (Fig. 25). Olher ^ 23% ^^ 1 Sowbugs ^"~~-^^^ 17% i ^^^ Caddisflies 15% Mayllies \ f ^^~-3^» Black llies ^ 10°0 L ^^^r Midges ScuU S Fishes Fish species, due to their greater mobility, tend to indicate envirormiental changes on a watershed scale. Total native fish species richness, fish species dominance, and the number of exotic and hybrid species are used as indicators of watershed disturbance. CTAP scientists sample fishes in randomly selected small streams — 30 CTAP sites are sam- pled each year with a total of 150 sites sampled over a five-year period. They also obtain samples from IDNR fisheries biologists who focus on larger streams. The IDNR fisheries samples are gathered from 514 stations in all 33 hydrologic units in Illinois over a five-year period. Approximately 160 IDNR fisheries sites are sampled c%'er)' \ear 'III '-t: 'l ^' mm. Fish Speci
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