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Population estimates for the four major insect orders are shown in Figure 2. Differences are <br />f apparent between taxonomic ou s <br />gr , p between sampling periods, and between stations along the <br />river reach. The lowest numbers in general were recorded for Plecoptera, with Ephemeroptera <br />consistently being the most numerous. Seasonal differences were noted in all groups; some of <br />the most dramatic differences occurred in the Plecoptera and Trichoptera populations in the <br />upper two upstream stations, where Plecopterans were more numerous in the spring and <br />Trichopterans more numerous in the fall counts. Over the entire river reach sampled, <br />Trichoptera counts generally were greater in the fall and Ephemeroptera were more numerous <br />in the spring. <br />The most obvious population differences between stations upstream of the discharge and those <br />downstream were noted in Diptera, which were significantly more numerous downstream. No <br />other group shows such a clear population change. Fall Trichoptera counts show large <br />populations in the two farthest upstream stations, but also some of their lowest numbers at the <br />two stations immediately upstream of the discharge. Figure 3 shows plots of EPT /C ratios <br />(combined numbers of Ephemeroptera, Plecoptera, and Trichoptera, divided by the number of <br />Chironomids), along with combined counts of the four groups. The ratios are consistently <br />smaller downstream of the discharge in data from both seasons, although a few small values <br />are noted in the upstream data, particularly from site U2. <br />Table 3 shows calculated values of Simpson's index of diversity, I, for each sample station, <br />based on all macroinvertebrate taxa identified. The index shows a great deal of variability <br />among stations. Means of the upstream stations do not significantly differ from those of the <br />downstream stations. Seasonal means are also similar. <br />Other Observations: <br />During the course of several site visits, there were incidental observations of other organisms <br />associated with the aquatic or riparian habitat. On several occasions we observed American <br />dippers feeding on aquatic insects among the partially submerged boulders in the channel. On <br />two occasions we observed a belted kingfisher, which feeds on small fish. We did not observe <br />the kingfisher feeding. On one occasion during the March Sampling trip a bald eagle was <br />observed flying overhead, and past inventories by the Division of Wildlife have shown a <br />winter population of at least seven bald eagles between Hotchkiss and the Paonia Dam <br />(Colorado Department of Highways, 1978). On three occasions we observed mallards flying <br />along the river channel. We also observed minnows at the water's edge above and below the <br />discharge point, and on three occasions observed small trout upstream of the discharge, but <br />were unable to identify the species. The riparian reconnaissance revealed numerous past sign <br />of beaver (gnawed branches and trunks of cottonwoods, severed willow stems), 'one fox and <br />one coyote was observed, and several mule deer and three elk were seen in the vicinity. <br />10 <br />13 <br />