Comparison of Infiltration Flux in Playa Lakes in Grassland and Cropland Basins, Southern High Plains of Texas

Playas are the dominant wetland type on the Southern High Plains of Texas and capture runoff during periods of heavy rainfall. Observing the hydrologic functions of playas is important to evaluate their ecological services, which include encouragement of species biodiversity and recharge of the underlying High Plains (Ogallala) Aquifer. Ten pairs of playas were chosen in 10 counties on the Texas Southern High Plains. Each pair included 1 playa surrounded by natural grassland (not in the Natural Resources Conservation Service's Conservation Reserve Program) and 1 playa surrounded by cultivated cropland. Instrumentation at each playa allowed calculation of changes in free water evaporation and water stored over time during the hydroperiods, defined as continuous durations of surface water storage in the playa basins, caused by one or more rainfall events that generated sufficient runoff flows to reach and fill the playas. A water budget model calculated daily infiltration flux through the playa bottoms. Six cropland playas and 3 grassland playas had significant hydroperiods with associated consistent instrumentation operation during the 6-year study across the years 2005 to 2011. The average observed infiltration flux rates were approximately 10 millimeters/day (range 2 to 20 millimeters/day) and 3 millimeters/day (range 1 to 5 millimeters/day) for the cropland and grassland playas, respectively. The preliminary results may be influenced by the presence of eroded sediments from the surrounding cropland, but more runoff events are needed to differentiate between the impacts of playa floor soils and variations in rainfall and playa watershed characteristics that contribute to the hydroperiods.