ISFAPPC04246

• Case Number: 00CW0101
• Stream Name: Fourmile Creek
• Watershed: Fourmile Creek
• Water Division: 2
• Water District: 12
• County: Fremont
• Instream Flow App - Doc Type: Supplemental Data

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The U.S. EPA (EPA) has developed a s,et of metrics (subsets and percentages of
macroinvertebrate raw data) proposed for use when evaluating macroinvertebrate
community structure,' instead of merely compa~ing species, numbers and total number of
taxa. One example of a tabulated metric i.s the percent EPT taxa (EPT refers to
Ephemeroptera, Plecoptera and Trichoptera). These groups prefer cold, clean, clear water
and are considered the "clean" water species for the Rocky Mountains, One would expect
a clean, cold-water Rocky Mountain stream to be dominated by a combination of these
three taxa, Thus, community structure can be evaluated partially by the percentage of
EPT taxa present relative to the total number of taxa collected.
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The three EPT orders consistently comprised about 50% of the total taxa collected
at all stations in 1994 and 1995 with one exception (Table 7), The percent of EPT taxa
was only 40% in 1995 in Fourmile Creek down:stream of Cripple Creek,

Ephemeroptera may be more sensitive to some metals than trout. The percentage
of Ephemeroptera individuals collected relative to the total number of individuals collected
ranged from 2,5% to 22%. The range was low compared to other small Colorado trout
streams where from 14% to 60% of the total nUniber of organisms collected were mayflies
(DOW unpublished data Eagle River and Alaniosa River),

3.2.2 Cripple Creek
The number of macroinvertebrate taxa collected in Cripple Creek was lower than
in. Fourmile Creek (Table 9). At the Cripple Creek sampling sites just upstream and
downstream of Ariqua Gulch, numbers of macroinvertebrates collected decreased by 90%
or more in comparison to Fourmile Creek sites, The presence of 20 or more taxa and
hundreds of organisms is normal in other Colo~ado streams similar in size and elevation
to Cripple Creek near Ariqua Gulch. There iwere fewer macroinvertebrate taxa and .
numbers of macroinvertebrates in Cripple Creek hear Ariqua Gulch than normally expected
in a Colorado mountain headwater stream of similar size and elevation.

Trichoptera were the dominant taxa in Cripple Creek (Table 9). The Trichoptera
Hesperophylax sp. was the dominant taxa at 'he sites in Cripple Creek upstream and
downstream of Ariqua Gulch, while Hydropsycne sp. was the most abundant taxa at the
confluence of Fourmile Creek, Hesperophylax sR. feed on plant material that falls into the
stream from the bank. Taxa that consume plants by shredding the material with mouth
parts often dominate the macroinvertebrates in headwater, high- elevation streams, such
as Cripple Creek near Ariqua Gulch. One Dipteran species, Umnophora aequifrons,
collected from Cripple Creek upstream and downstream of Ariqua Gulch was the only
species collected in another Colorado mountaitl stream contaminated by effluent from a
domestic wastewater treatment plant and by imetals from active and inactive mining
operations,

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