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 measured and metal concentrations were at or near detection levels. Hardness levels of 400 mg/L do mitigate toxic impacts of low metal concentrations. 5.0 DISCUSSION Overall, water quality data for Fourmile Creek shows no potential harm to the aquatic community. The high hardness levels at the lower three stations would mitigate metals impacts. However, metal concentrations are at or near detection levels. Station One, the control station, was the only station to measure a low hardness of 100 mg/L CaC03 with higher cadmium concentrations of 1.7 total and 2.8 dissolved ug/L. Exposure at 1.86 ug/L of cadmium for seven weeks to acclimated brown trout fry resulted in 0% mortality and 63% mortality at 3.13 ug/L (Davies 1990). At the cadmium levels of Fourmile Creek, no impacts to brown trout would be expected. Mayflies, ,caddisflies, stoneflies were found at all locations, except Station Four where no stoneflies were collected. The presence of these three groups may be indicative of a typical, relative unpolluted Rocky Mountain trout stream. At Station Four, stoneflies were absent while Atherix pachypus, Ophio!!omphus, and Tricorythodes were common. These three taxa can tolerate siltation while stoneflies can be eliminated by sediment. Perhaps, siltation is increased at this lower station, but not enough to cause significant damage to the aquatic community. Fourmile Creek has reproducing brown trout populations throughout the study reach as shown by the presence of young trout (approximately 7-10 centimeters) and large trout (approximately 37-40 centimeters). There are also reproducing populations of the two forage species, the longnose dace and white sucker, throughout the study reach. Other forage species such as the fathead minnow, white sucker, and creek chub were found at some of the stations. There are few Colorado brown trout streams with this many forage species (Woodling personal communication). Vannote et al. (1980) described a river continuum concept where from headwaters to mouth, physical parameters of a river "present a continuous gr~ient of physical__C9nditiORs." This gradient of physical conaitions results in a "continuum of biotic adjustments" and that "structural characteristics" of stream communities conform to the location of the river along the continuum. As a result, streams of a similar classification can be expected to have many physical aspects similar to other streams of the same classification. "As stream order increased... total combined fish increased per length of stream..." At Station One, Fourmile Creek is a fourth order stream, and as the creek flows downstream, it becomes a fifth order stream at the mouth. "Fourth-order streams contained the most species." Six different species of fish were found at Station One (a fourth-order stream). Brook, brown, and rainbow trout along with white suckers, longnose dace, and longnose suckers were collected at this station. Fourmile Creek is somewhat unique in that normally only three species of fish are found in a small Colorado trout stream. Overall, Fourmile Creek is a good brown trout stream. This stream is a little unusual in the sense that it flows north to south along the front range between mountains and plains. It is a , sort of transition zone stream and shows some plains stream characteristics such as the presence , of the fathead minnow, creek chub, and dragonflies. The presence of reproducing brown trout