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<br />I <br /> <br />152 UTAH ACADEMY PROCEEDINGS, VOL. 45, PART 1, 1968 <br />Turbidity <br />Water released from the reservoir was clear during 1964-67, <br />but three major tributaries discharged turbid waters into the <br />Green River within the study area. These were Red Creek (18.0 <br />KBD), Vermillion Creek (70.2 KBD), and the Yampa River (105.9 <br />KBD). Red and Vermillion creeks are small (0-0.6 M3 /see in <br />summer) while the Yampa River nearly equals the Green (mean <br />annual flow during 1963-67 = 49.1 m3/sec). Maximum turbidities <br />recorded at Little Hole, Carr Ranch, Echo Park, and Island <br />Park in 1964-65 were 62, 700, 5000, and 5000 JTU (Jackson Turbidity <br />Units), respectively. <br />Water Chemistry <br />Dissolved-oxygen concentrations were 6.0 ppm or higher at <br />all stations. Highest levels were observed at Little Hole (13.0 <br />ppm), where summer water temperatures were low, the water <br />was clear, and algal growths on the bottom were extensive. <br />The pH at all stations combined varied from 7.7 to 8.9 and no <br />seasonal trends were apparent. Records from the U. S. Geologi- <br />cal Survey indicate that the mean hydrogen-ion concentration of <br />the Green River at Greendale has remained at 7.8 during pre- and <br />postimpoundment years. <br />Total alkalinity was 125-180 ppm between the dam and Echo <br />Park during 1.964-65. Alkalinity of the Yampa River was lower <br />than that of the Green during these years (52-155 ppm), particu- <br />larly during the spring-runoff period. As a result, alkalinity at <br />Island Park was lower (65-155 ppm) than that observed above <br />Echo Park. <br />MACROINVERTEBRATE DISTRIBUTION; 1964.1965 <br />(FLAMING GORGE DAM TO ISLAND PARK) <br />During 1964-1965, 69 different invertebrate forms were col- <br />lected in the study area (Table 3). Included were 28 species of <br />Ephemeroptera, 4 genera of Poeoptera, 7 genera of Trichoptera, <br />10 families of Diptera, and 5 families of Coleoptera. The number <br />of taxonomic groups collected at each station increased and the <br />density of bottom fauna on each type of substrate decreased pro- <br />gressively downstream from Flaming Gorge Dam. Detailed analyses <br />of the bottom-sample data are contained in Pearson (1967). <br />11 <br />