USING POREWATER CHEMISTRY AND STABLE ISOTOPES TO INVESTIGATE PHOSPHORUS ADDITION TO UTAH LAKE, UTAH

Quantifying natural inputs of phosphorus (P) into lacustrine systems is essential for nutrient management decisions. The addition of P through lake sediment porewater has not been well studied, but recent work has shown significant potential.

We present the P diffusive and advective porewater gradients from two sediment freeze cores from Utah Lake, Utah collected in fall 2024. One core was taken mid-lake to represent a deep-water location (UTL24-DW) and the other core was taken between the Lindon Marina and Timpanogos Special Service District representing a near shore location adjacent to a wastewater treatment plant (UTL24-TSSD).

Using stable hydrogen (δ²H) and oxygen (δ¹⁸O) isotopes along with geochemical analysis of the porewater, we compare near shore versus deep water P fluxes. Analysis showed minimal distinction in the UTL24-DW δ²H / δ¹⁸O isotope values with depth, but a notable P diffusion gradient out of the sediment porewater was identified. In contrast, isotopes in UTL24-TSSD porewater indicated groundwater/ evaporated lake water mixing, while geochemistry showed disrupted P diffusion gradients. We believe storm disruption of shallow sediment and groundwater influence are potential causes for P diffusion differences in the cores

In conclusion, UTL24-DW exhibits P additions by diffusion only while UTL24-TSSD exhibits P addition by diffusion and advection. Further Utah Lake freeze cores will be needed to expand the applicability of these results throughout the lake and determine more precise P fluxes porewater.