The response of Playa and Sabkha hydraulics and mineralogy to climate forcing

Abstract

Dry playa lakes and sabkhat often represent the terminus of large ground water flow systems and act as integrators of both up gradient (recharge) and down gradient discharge (evaporation). Ground water levels beneath playa/sabkha systems show a variety of surprising responses driven by large evaporation demands and chemical processes not typically encountered in more humid regions. When the water table is very close to the land surface, almost instantaneous rises can be observed with little observed change in either up-gradient ground water recharge or potential evaporation. Conversely, when water tables are several meters below the playa surface, water table responses to inter-annual variability of recharge can be damped and lag significantly behind such changes. In this review of the dynamics of shallow water tables in playa lakes and sabkat, we discuss the pertinent hydraulic and solute processes and extract a simple but comprehensive model based on soil physics for predicting the water table response to either upstream recharge changes or changes in potential evaporation at the playa/sabkha. Solutes and associated authigenic minerals are also shown to be very important in discriminating both the causes and effects of water level fluctuations.