Dames & Moore, 1999 - USDA Forest Service

Species Richness
Species richness provides an indication of community health through a measurement of the variety of taxa
(species) present. Species richness generally increases with increasing water quality, habitat diversity,
andor habitat suitability (EPA, 1989). As indicated from the 1997 benthic macroinvertebrate sampling
results, species richness at the reference locations ranged from 37 at SFAC-I to 52 at BC-I while locations
downstream from the Site ranged from 9 at RC-5a to 37 at RC-9.
Ratio of Scrapers to Filtering Collectors
The scraper and filtering collector functional feeding group ratio reflects the possible unbalanced
community responding to an overabundance of a particular food source. Scrapers are usually herbivorous
and typically feed on periphyton (attached algae) while filtering collectors will gather food that is suspended
in the water column. The overabundance of scrapers indicates the presence of periphyton while the opposite
imbalance reflects the possible lack of periphyton. The ratio of scrapers to filtering collectors at the
reference locations ranged from 0.8 1 at CoC- 1 to 0.92 at SFAC- I. Locations downstream from the Site
ranged from 0 (locations RC-7,5a, and 10) to 0.78 (RC-9).
Ratio of EPT Taxa and Chironomid Abundance
The EPT and Chironomidae abundance also provides an indication of relative benthic macroinvertebrate
community health. Good biotic condition is reflected in communities having a fairly even distribution
among all four major groups and with substantial representation in the sensitive groups Ephemeroptera,
Plecoptera, and Trichoptera (EPA, 1989). Populations having more Chironomids relative to the EPT group
may indicate environmental stress. EPT taxa and Chironomid ratios at the reference locations ranged from
0.93 at RC-6 to 0.97 at SFAC- I. Downstream from the Site this index ranged from 0.40 at RC-5a to 0.82 at
RC-9.
Percent Contribution of Dominant Taxa
The percent of contribution of the numerically dominant taxon to the total number of organisms is an
indication of benthic macroinvertebrate community balance at the lowest positive taxonomic level (EPA,
1989). A community dominated by relatively few taxa would be considered under stress. Dominant taxa
contributions at the reference locations ranged from 30 percent at RC-6 and BC-1 to 44 percent at SFAC-I
while downstream from the Site this index ranged from 12 percent at RC-9 to 54 percent at RC-5a.
EPT' Index
Similar to the EPT Taxa and Chironomid ratio, the EPT index reflects the total number of distinct taxa
within the orders Epherneroptera, Plecoptera, and Tricoptera. The index generally increases with increasing
water quality. The EPT index at the reference locations was generally consistent ranging from 26 at SFAC-
1 to 36 at BC-1 while the EPT index at the locations downstream from the Site ranged from 5 at RC-Sa to
25 at RC-9.
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17693-005-01 9Uuly 19. 1999;4:5 1 PM;DRAFT FINAL RI REPORT