Eutrophication Assessment of Mt. Dell Reservoir

The degree and possible causes of eutrophication in Mt. Dell Reservoir, a small water supply reservoir in Parleys Canyon above Salt Lake City, were examined with a number of limnological studes. These studies described external (incoming stream flow) and internal (sediment) nutrient sources, general limnology, nutrient limitations, and trophic state. A monthly program of sampling at selected stream sites determined taht one area of mixed agricultural and undistrubed rangeland contributed significant amounts of total soluble inorganic nitrogen. Sediment phosphorus uptake and release rates were determined with aquatic three-phase microcosms. The results indicated that sediment phosphorus mass loadings were small (less than 5% of the total loading) compared to stream phosphorus mass loadings if the hypolimnion is aerobic. Anoxic conditions could cause sediment phosphorus releases to be greater than stream phosphorus mass loadings (about 68% of the total). Descriptive limnologies indicated that the reservoir was alkaline (pH about 8.0 and alkalinities usually around 200 mg CaCO3.a), dimictic, weakly stratified, and usually well oxygenated. Nutrient levels were usually highest during the winter and at greater depths. Highest total phosphorus and orthophosphate levels were generally within a range of 50-100 ug/l whereas total nitrogen and total soluble inorganic nitrogen concentrations ranged from 0.1 to 2.0 mg/l. Blue-green algae were the dominant algal type comprising 80 percent of the total algal composition. Algae were most numerous and chlorophyl