Authors: Rebecca Butters, Gustavious Williams, Anna Cardall, Amber Gurecki, Megan Jones, Jacob Taggart, Kaylee Tanner, Rachel Valek – Brigham Young University
Title: Nutrients in Utah Lake Behave as a Buffered System: Suspended Sediments and Sorption Impacts on Water Column Phosphate Concentrations
Abstract: In freshwater lakes, nutrient concentrations and cycling are complicated processes. Utah Lake is unique due to its large surface area and shallow depth, which results in high suspended and dissolved solids. Significant evaporation rates and low outflow rates relative to inflow also mean that water is saturated with several influential nutrients, including phosphorus. This has led to frequent, extensive harmful algae blooms that have created an ecosystem that is dangerous to native wildlife in the lake and nearby wilderness areas as well as to human populations in the dense cities bordering the lake. It is established that the lake water geochemistry and the role of benthic sediments and suspended solids as a sorption system can affect phosphorus concentrations in the water column. 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 10-meter diameter mesocosms within the lake. We characterized P partitioning between dissolved and sorbed phases and within the lakebed sediment fractions. 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 process 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 maintained relatively constant by lake processes that compensated for artificial changes in water column nutrient loads. Our conclusions inform discourse regarding the effectiveness of phosphorus-input-limiting strategies in the restoration of the Utah Lake ecosystem from a eutrophic state by demonstrating that the phosphorus sinks and sources in the lake will act to maintain a constant concentration of phosphorus in response to changes in phosphorus input.