Changes in Water Quality as Related to Retention Time Within Red Rock Reservoir, Iowa, Summer 1972
Clark, Larry James
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The problem. To determine what changes in water quality occur as water enters and moves through Red Rock Reservoir during the summer of 1972. Procedure. Three stations representing different areas of the lake were sampled twice weekly from June 9 to August 1, 1972. Water samples were collected at 0.5, 1.5, 3.5 and 7.0 meters with temperature data recorded. Specific conductance, pH, dissolved carbon dioxide, dissolved oxygen and alkalinity were determined in the field. Samples were refrigerated and returned to the laboratory for the determination of nitrates, phosphates and sulfates. Findings. Weak thermal stratification occurred in late June and early July but was prevented from becoming stable by high inflow. The average retention time was 11.7 days. The reservoir water was completely replenished five times during the study. No correlation was found between retention time and pH, specific conductance, dissolved carbon dioxide, dissolved oxygen and alkalinity. Increased inflow produced high nitrate, phosphate and sulfate values. Conclusions. The existing high nutrient levels indicate that Red Rock is a productive lake during the summer, however the high flushing rate could prevent the development of plankton populations and retard further eutrophication. Recommendations. Further work involving nutrient cycles, regeneration and supply in reservoirs is needed. Red Rock Reservoir should be studied during periods in which strong thermal stratification occurs which might distinguish upper and lower basins as well as vertical chemical differences. The effect of the stream regulation, brought about by the completion of Saylorville Reservoir, on Red Rock Reservoir should be investigated.
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