Metric

Description

Expected Response to Impairment

Richness Measures

Taxa Richness

Total number of individual taxa (genera, or lowest taxonomic level identified)

decrease

EPT Taxa

Number of taxa in the Ephemeroptera (mayfly), Plecoptera (stonefly) and Trichoptera (caddishfly) insect orders

decrease

Ephemeroptera Taxa

Number of mayfly taxa (genera)

decrease

Plecoptera Taxa

Number of stonefly taxa (genera)

decrease

Trichoptera Taxa

Number of caddisfly taxa (genera)

decrease

Composition Measures

EPT Index

Percent composition of mayfly, stonefly and caddisfly larve

decrease

Sensitive EPT Index

Percent composition of mayfly, stonefly and caddisfly larve with Tolerance Values of 0 through 3

decrease

Shannon Diversity Index

General measures of sample diversity that incorporates richness and evenness

decrease

Tolerance/Intolerance Measures

Tolerance Value

Value between 0 and 10 weighed for abundance of individuals designated as pollution tolerant (higher values) and intolerant (lower values)

increase

Percent Intolerant Ogranisms

Percent of organisms in sample that are highly intolerant to impairment as indicated by a tolerance value of 0, 1 or 2

decrease

Percent Tolerant Organisms

Percent of organism in sample that are highly tolerant to impairment as indicated by a tolerance value of 8, 9, or 10

increase

Percent Hydropsychidae

Percent of organisms in the caddisfly family Hydropsychidae

increase

Percent Baetidae

Percent of organisms in the mayfly family Baetidae

increase

Percent Dominant Taxa

Percent composition of the single most abundant taxon

increase

Functional Feeding Groups

Percent Collectors

Percent composition of taxa that collect or gather fine particulate matter

increase

Percent Filterers

Percent composition of taxa that filter fine particulate matter

increase

Percent Scrapers (Grazers)

Percent composition of taxa that graze upon periphyton

variable

Percent Predators

Percent composition of taxa that feed on other organisms

variable

Percent Shredders

Percent composition of taxa that shreds coarse particulate matter

decrease