Diurnal to seasonal dynamics of saline pan evaporation and groundwater level fluctuations, Bonneville Salt Flats, Utah, USA

Abstract

Saline pans are environments with ephemeral to persistent evaporite crusts, surface and groundwater brine, little to no vegetation, and low topographic gradients. These characteristics make them sensitive to diverse hydrological processes. This research provides guidance on assessing and interpreting fluctuations in saline pan groundwater levels. Observations from the center of the Bonneville Salt Flats, Utah, USA, focused on meteorological and groundwater level fluctuations and were used to quantify evaporation and identify natural environmental controls on saline pan groundwater level variation. Primary water fluxes consist of precipitation and evaporation. Eddy-covariance evaporation measurements, spanning over 1.5 years and capturing diverse surface conditions, were collected. An artificial neural network, trained on meteorological measurements and eddy-covariance-measured evaporation, estimated evaporation over a 6-year period. The saline pan has two states: (1) dry, when water availability rather than evaporative potential limits evaporation, and (2) wet, when evaporative potential limits evaporation. In dry conditions, characterized by evaporation rates of ~0.1 mm/day, groundwater levels with daily average depths ≥5 cm below the surface, demonstrated daily variations >6 cm during summer and seasonal fluctuations >50 cm in response to temperature changes. Groundwater levels did not respond to temperature changes when there was surface water. Groundwater levels rose to the surface under wet conditions. Over multiple years, the system is in balance, with evaporation equaling precipitation.