Coprecipitation of Phosphorus With Calcium Carbonate in Bear Lake, Utah - Idaho

Monitoring of Bear Lake was conducted in 1981 and 1982 to describe the current limnology and trophic state of the lake. The nutrientt loadings of various parameters were measured from April, 1981 through June, 1982. The rate of coprecipitation of phosphorus was determined for different initial phosphorus concentrations by use of non-algal assays. Algal bioassays with Selenastrum capricornutum were used to determine the reduction in potential algal biomass as a result of the coprecipitation of phosphorus. The lake exhibit-.ed chemical characteristics indicative of mesotrophy or eutrophy. Total phosphorus values averaged 11μg/1 for 1981 and 20 μg/1 for 1982. A hypolimnetic accumulation of phosphorus was also not:ed for the stratified periods. Addittionally, hypolimnetic oxygen deficit values were indicative of mesotrophy in 1981 and eutrophy in 1982. The chlorophyll concentrations were characteristic of oligotrophic conditions during both years however. Phosphorus was found to be limiting production approximately 85% of the year. The Bear River Contributed approximately 60% of the total phosphorus loading to the lake in 1981 and 50% in 1982. Overall, the total phophorus loading increased 195% between the dry year, 1981, and the wet year, 1982. Vollenweider\u27s (1976) phosphorus loading model described the loading to Bear Lake as indicative of mesotrophic conditions in 1981 and eutrophic conditions in 1982. Calcium and magnesium concentrations fluctuated widely throughout the year. The Mg:Ca molar ratio varied from 1:1 in the spring to 3.5:1 in the fall. Total hardness values did not vary in response to the changing ionic concentrations and this was attributed to preferential replacement of precipitated calcium by the Bear River inflow. Non-algal assays quantified the removal of phosphorus by coprecipitation at increasing initial phosphorus by concentration. The rate of removal initial decreased substantially as phosphorus levels increased with a shift in reaction order from second order to first order noted at approximately 50 μg/1. Predictive models were derived from the initial assays and verified with data from a separate experiment which use filtered Bear Lake water. The models accurately predicted the amount of phosphorus removed by coprecipitation at all phosphorus levels. Algal bioassays in synthetic Bear Lake and soft-water media were used to evaluate the efficiency of the coprecipitation mechanism when in competition with algae for phosphorus. An average reduction in biomass of 40% was noted between the media at similar nutrient levels