ISFAPPC04246 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I. I I 5 '. concentrations would be toxic to trout at the normal hardness levels of most Colorado mountain streams, At the elevated hardness of Ariqua Gulch (500 mglJ), these metal levels probably would not be toxic to trout. 3.2 Macroinvertebrates 3.2.1 Fourmile Creek Three orders of aquatic insects, Ephemeroptera (mayflies), Plecoptera (stoneflies) and Trichoptera (caddis flies), were abundant in both 1994 and 1995 in Fourmile Creek (Table 6), In addition Diptera and Coleoptera were also found in each collection. The orders Ephemeroptera, Plecoptera and Trichoptera are generally considered to be indicators of clean water, Raw data from 1994 and 1995 sampling efforts are presented in Appendix A and B. The total number of taxa collected in 1994 and 1995 ranged from 22 to 37 in Founnile Creek (Table 7). The number of organisms collected varied from 380 to 1,453. These results were similar to other Colorado mountain trout l?treams, In general the numbers of organisms and taxa collected indicate an abundant. diverse food source for fish in Fourmile Creek, Some of the individual taxa collected in Founnile Creek, Simulium sp., Hydropsyche sp" and Brachycentrus accidenta/is, are filter feeders often associated with clear, fast- flowing, low-sediment waters typical of Colorado mountain trout streams, Filter feeders either spin a net to collect food that drifts by in the current or use specially adapted body parts, such as antenna or legs, for the same purpose, Other taxa, such as Atherix pachypus, Ophiogomphus severus (a dragon fly) and Ambrysus sp., are associated with slower-moving waters with relatively high sedimentation, These species are more often found in lower-elevation waters and seldom found by the DOW in trout streams, The presence of these wannwater taxa is an indication that Founnile Creek is a transition-zone stream where a coldwater ecosystem changes to a warmwater ecosytem in Fourmile Creek, In 1995, the predatory stonefly H6speroper/a pacifica was collected at three sites: upstream of Cripple Creek, downstream of Cripple Creek and downstream of the Carlton tunnel. This species has a two-or three-year life cycle, with two-or three-year old nymphs much larger thaIH>De-year old organisms, Two-or three-year old nymphs were abundant at the site upstream of Cripple Creek, Only one older nymph was collected in Fourmile Creek downstream of Cripple Creek. The remainder of the Hesperoperla paqifica collected downstream of Cripple Creek were smaller one-year-old nymphs. Although aquatic macroinvertebrates have a patchy distribution across a stream substrate, the absence of older nymphs was puzzling since the DOW macroinvertebrate methods collect organisms from several square meters of stream substrate. The older nymphs may have been removed by an environmental disturbance.