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23 C <br />=-had increased-to 5.0 ppm 0.2 miles below the dam, and to 9.0 ppm at <br />Little Hole, 7.2 miles below (data from unpublished records of the Utah <br />State Department of Fish and Game). Pfitzer (1963) reported a much <br />- slower reaeration of waters low in oxygen released from reservoirs in <br />Tennessee (2-4 ppm in 3 miles). The tailwaters he studied had dense <br />growths of algae on the substrate, but the temperature of the water <br />---(70-72°F.) was higher°than the Green-and the gradient was probably less. <br />Nighttime reaeration rates were not significantly lower than daytime <br />rates in his reported data. To what extent oxygenation or deoxygenation <br />-- -- - -af the- water -took-place in -the Green River during winter months or -at <br />night is not known. <br />Dissolved Solids <br />Concentration of total dissolved solids in the Green River in- ?. <br />creased noticeably after impoundment. Most of the increase was in sul- <br />fates, calcium, sodium, and bicarbonates (Table 7). Bicarbonate deter- <br />minations made by the U. S. Geological Survey at Greendale were consis- <br />tently around 192 ppm during 1964-65 whereas determinations made in the <br />present study were consistently around 140 ppm at Little Hole, only <br />6.7 miles below the Greendale station. This discrepency may be due <br />partly to a different treatment of water samples (U.S.G.S. samples <br />were stored prior to analysis, present study samples were analyzed im- <br />mediately). <br />Total alkalinity between the dam and Echo Park was in the 125-180 <br />ppm range during 1964-5. Alkalinity of the Yampa River was lower than <br />the Green during both years (52-155 ppm), particularly during the <br />spring runoff season. Consequently, alkalinity at Island Park was low-