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<br />Simpson - Simpson's (46) diversity index is defined as the probability of picking <br />two individuals that are of the same group. Abundant taxa receive more weight. <br />Values range from 0-1; the higher the number the greater the diversity. <br /> <br />Evenness - Evenness is a measure of the distribution of taxa within a community. <br />The evenness index used in this report is that recommended by Ludwig and Reynolds <br />(87). Values range from 0-1 and approach zero as a single taxon becomes more <br />dominant. <br /> <br />Biotic indices <br />Biotic indices make use of the indicator taxa concept. Taxa are assigned water <br />quality tolerance values (TV) or quotients (TQ) based on their tolerance to <br />pollution. The most common biotic indices in use in the united States are the <br />modified Hilsenhoff Biotic Index and the USFS Biotic Condition Index. <br /> <br />Modified Hilsenhoff Biotic Index - This index has been used to detect nutrient <br />enrichment, high sediment loads, low dissolved oxygen, and thermal impacts. It <br />is best at detecting organic pollution. All taxa are assigned a TV from 0 - for <br />taxa known to occur only in high quality water, to 10 - for taxa known to occur <br />in severely polluted waters. TV values came from Hilsenhoff (43, 44) and Bode <br />et al. (45). The MHBI is calculated by multiplying the TV for each taxon by the <br />taxon abundance, summing the products, and dividing by the number total sample <br />abundance. Waters with values 0-2 are considered clean, 2-4 slightly enriched, <br />4-7 enriched, and 7-10 polluted. <br /> <br />USFS Community tolerant quotient/biotic condition index - <br />Unimpacted benthic aquatic macro invertebrate community structure (CTQp) is <br />predicted based on total alkalinity, sulfate, substrate size, and stream <br />gradient. The actual benthic aquatic macroinvertebrate community structure <br />(CTQd) corrected for taxa dominance is then divided by the CTQp and multiplied <br />by 1030 to determine the biotic condition index (BCI). All taxa are assigned a <br />TQ from 0- pollution intolerant, to 108 - pollution tolerant (84). Waters having <br />a BCls >90 are considered excellent, 80-90 good, 72-79 fair, and <72 poor. This <br />index has been widely used by the USFS and BLM in the western United States. <br /> <br />Functional feeding group classifica~ion <br /> <br />Shredders - Shredders utilize coarse particulate organic matter (CPOM). They <br />are sensitive to changes in riparian vegetation and can be good indicators of <br />the presence of toxicants. Xylophages are shredders which eat wood and are <br />typically long lived. <br /> <br />Scrapers - Scrapers feed on periphyton (attached algae and associated material). <br />Scraper populations increase with increasing abundance of diatoms and decrease <br />as filamentous algae, mosses, and vascular plants increase. Scrapers decrease <br />in relative abundance in response to sedimentation and organic pollution. <br /> <br />Collector-filterers - Collector-filterers feed on suspended fine particulate <br />organic matter (FPOM). Collector-filterers are sensitive to toxicants attached <br />to suspended particles. <br /> <br />Collector-gatherers - Collector-gatherers feed on deposited fine particulate <br />organic matter. Collector-gatherers are sensitive to deposited toxicants. <br /> <br />Predators <br /> <br />Predators feed on living animal tissue. <br /> <br />Parasites Internal parasites of eggs, larvae and pupae. External parasites of <br />larvae, prepupae and pupae in cocoons, pupal cases or mines, and adult spiders. <br />