DIURNAL TO SEASONAL HYDROLOGICAL FLUCTUATIONS IN SALINE PANS, EXAMPLES FROM THE BONNEVILLE SALT FLATS, UTAH

In 1994, Michael Rosen advanced our knowledge of playas by synthesizing and highlighting the importance of groundwater in playa development and preservation. Saline pans and playas are becoming increasingly important because rising groundwater extraction and mineral resource development are altering these extensive landscapes, sometimes leading to increased dust production and associated respiratory health problems. This research uses hydrological observations of Utah’s Bonneville Salt Flats to build upon Michael Rosen’s work on halite dominated saline pans, specifically on daily to seasonal time scales. High-resolution meteorological, sedimentological, groundwater level, and water density measurements were collected over a five-year timespan from the center of the Bonneville Salt Flats. These measurements were used to determine that the halite crust is an effective evaporation barrier of the shallow groundwater table, helping to slow the transition from a saline pan to an ablation surface during periods of increased water extraction. The estimated net annual water budget is < ±1.5 cm/year. Groundwater and soil temperature measurements indicate seasonal to diurnal water level changes occur because of the effect of temperature fluctuations upon trapped soil vapor and matric potential. Groundwater halite saturation measurements demonstrate that, when paired with temperature-controlled groundwater level variations, temperature-controlled brine salinity fluctuations can redistribute halite within the saline crust and alter its texture. These results show that there is a high degree of diurnal to seasonal variation in saline pan groundwater. Knowledge of these variations, processes, and the self-regulating effect of saline pans upon hydrologic fluxes within arid basins can inform sedimentological interpretations and landscape monitoring and management decisions of these unique systems.