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<br />concentrations in Ouray backwaters may stimulate production of blue-green <br />algae; blue-green algae were a major component of the <25 ~m size-fraction of <br />phytoplankton (nannoplankton) collected from backwaters. The average increase <br />in turbidity in Ouray backwaters was due in part to greater nannoplankton <br />abundance and higher concentrations of particulate organic material. Seasonal <br />turbidity in BA 250.8 averaged 77 NTU in 1988, the highest seasonal average <br />for a backwater sampled during this study, due in part to high POM <br />concentrations in the <25 ~m size-fraction. Other Ouray backwaters averaged <br />53 NTU, while the river averaged 49 NTU. <br /> <br />Zooplankton densities were low in both the river and backwaters, although <br />greater in backwaters, and generally greater in Ouray backwaters than in <br />Island Park or Jensen backwaters. Zooplankton densities increased from 0.44 <br />individuals per liter in upstream Island Park backwaters to 1.5 individuals <br />per liter in downstream Ouray backwaters, although the magnitude of the <br />increase was not as great as with the <25 pm size-fraction of the blue-green <br />algae, which constituted the major component of this size-fraction. Among the <br />backwaters sampled, those larger backwaters with narrow connections to the <br />river, with a lower exchange rate and a greater retention time (BA 300.5 and <br />BA 251.0), generally had higher densities of zooplankton. <br /> <br />Continuous monitoring of temperature, DO, pH and specific conductance in one <br />backwater each at Island Park, Jensen, and Ouray revealed diel fluctuation in <br />these limnological parameters, with some of the fluctuations directly <br />influenced by changes in riverflow. Fluctuations in riverflow that increase <br />water level in backwaters result in importation of riverine nutrients and POM <br />into backwaters, as well as resuspension of organic material from the <br /> <br />4 <br />