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 number of organisms collected in Fourmile Creek downstream of Cripple Creek
increased from 467 in 1994 to 1,206 in 1995, The number of taxa collected remained
similar, 24 in 1994 'and 25 in 1995. The difference in numbers was due to increased
numbers of four taxa, It is not appropriate to state that the increase in the number of
organisms collected in 1995 versus 1994 at this one site represents an increase in quality
or abundance of macroinvertebrates at this site, '

Although the composition of macroinvertebrates and distribution remained relatively
the same from 1994 to 1995. some interesting observations were made, The number and
types of mayflies (Ephemeroptera) collected were less than in other Colorado mountain
streams, This may have been due to elevation. The portion of Fourmile Creek monitored
for this project is at a lower elevation than most other Colorado trout streams. Many
mayflies thrive in streams with a steep gradient, low sediment and low temperatures, At
the elevations within the study area, summer temperatures are higher than many mountain
areas, Stream gradient may be lower with a corresponding increase in sedimentation.
Taxa such as Atherix pachypus, Ophiogomphus severus (a dragon fly) and Ambrysus sp,
are associated with warmer, slower waters. It may be that Fourmile Creek in the study
area is a transition-zone ecosystem where a coldwater mountain stream gradually changes
to a warmwater plains stream,

Distribution of the stonefly, Hesperoperla pacifica, in the study area may indicate
that an environmental disturbance occurred downstream of Cripple Creek between 1994
and 1995. Hesperoperla pacifica has a multi-year life cycle. Two or three age classes of
nymphs should be present in a stream and can be differentiated based on size. Two or
three age classes of this stonefly were collected upstream of Cripple Creek while only
young first-year nymphs were found downstream of Cripple Creek in 1995, It may be that
an environmental disturbance removed older nymphs from the stream downstream of
Cripple Creek before the fall 1995 sampling. This observation could be a function of
natural variation. human activity, sampling technique or systematic error, Data collected
in the coming years will provide a better reference to determine if the change in the
numbers of this stonefly in 1995 reflected a real change in Fourmile Creek
macroinvertebrates.

4.1.3 Fish
Fourmile Creek contained a population of reproducing brown trout throughout the
study area from upstream of Cripple Creek downstream to the Lion's Resto[ation site. A
population of reproducing brook trout was found in Fourmile Creek upstream of Cripple
Creek. There were naturally reproducing populations of two forage species, longnose
dace and white suckers throughout the study area. Creek chubs maintained a naturally
reproducing population at the lowest site, Lion's Restoration. Few Colorado brown trout
streams have this high of a diversity of forage species.

The spatial distribution of aquatic communities can be explained somewhat by the
river continuum concept (Vannote 1980), The main idea of this concept is that the physical
parameters of a river from the headwaters to mouth "present a continuum of biotic