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beak <br />found at each station (Table 5.0-3). Numerically the most abundant components <br />. of the benthos were caddisfly larvae (primarily the net-spinning Hydropsychidae) <br />and mayfly nymphs (Baetidae, Ephemerellidae, Heptageniidae). Together these <br />two faunal groups comprised over 79% of total faunal numbers at all stations <br />(Table 5.0-2). These organisms, as well as the stonefly nymphs (Plecoptera), <br />require quality water conditions which include high concentrations of dis- <br />solved oxygen. relatively swift currents, relatively cool maximum temperatures, <br />and low concentrations of toxic chemicals (Hynes 1970; Cairns and Dickson <br />1971, 1977). The mean maximum temperature of 15oC in the North Fork Gunnison <br />River recorded at Somerset is well within tolerance for these organisms <br />(Hubbard and Peters 1978; Harris and Lawrence 1978). As previously reported, <br />dissolved oxygen measurements at all stations exceeded 100% saturation <br />(Table 3.0-1). <br />• Mean total densities (number/m2) of benthic organisms ranged from <br />2166/m2 at Station F to 5036/m2 at Station D (Table 5.0-3). Analysis of <br />variance procedures were used to compare mean total densities at Stations <br />B through E. Significant differences among stations were found (F(3,6) _ <br />6.71, p<0.05). Tukey's HSD test was subsequently used to compare densities <br />at individual stations. Results showed that mean total density of benthic <br />fauna at Station D was significantly higher (p<0.05) than at Station F. The <br />reason for the observed difference was not apparent from a biological or <br />environmental standpoint. <br />Mean total densities for combined stations was 3356/m2. By comparison, <br />the Bureau of Land Management (1979) reported an average total density of <br />950/m2 for the North Fork Gunnison River adjacent to ARCO's Nt. Gunnison <br />• permit area just downstream from Hawk's Nest. <br />5-6 <br />