Nutrients in Utah Lake Behave as a Buffered System: Suspended Sediments and Sorption Impacts on Water Column Phosphate Concentrations

In freshwater lakes, nutrient concentrations and cycling are complicated processes. The lake water geochemistry, the influence of benthic sediments, and the role of suspended solids as a sorption system can affect phosphorus concentrations in the water column. Utah Lake has complicated geochemistry. The shallow lake has high suspended and dissolved solids, and because of significant evaporation, the water is saturated with regard to calcite. We designed the Utah Lake Nutrient Cycling Studies Phosphorus Addition Experiment to characterize phosphorus fluxes between the sediment and water column in Utah Lake. We conducted both bench-scale experiments with water and sediment collected from Utah Lake, as well as in-situ experiments in large, 10-meter diameter mesocosms within the lake. We characterized P partitioning between dissolved and sorbed phases. We assumed that any P in the water column that is not in the dissolved fraction, is sorbed. This includes colloidal and particulate P from precipitation, and P that has been taken up by organisms in the water column. By analyzing this data, we improved our understanding of internal P loadings in Utah Lake and quantified the rate of P partitioning between the dissolved and sorbed fractions and the actual phosphate partitioning between dissolved and sorbed phases. Because of strong sorption and precipitation, we found that dissolved water column concentrations of P were relatively constant, independent of nutrient loads. Our conclusions inform discourse regarding the effectiveness of phosphorus-waste-limiting strategies in the restoration of the Utah Lake ecosystem by demonstrating that the phosphorus sinks and sources in the lake will act to maintain a constant concentration of phosphorus in response to change in phosphorus input.