Ecological controls on the water cycle inwWater limited ecosystems. Scanlon, Bridget ^*,1, Reedy, Robert¹, ¹ Univ. of Texas at Austin, Austin, TX

ABSTRACT- Vegetation dynamics in desert regions plays a critical role in the water cycle and regulates water cycle response to climate variability at interannual to millennial time scales and from point to regional spatial scales. Water potential was monitored for long-time periods (5 to 12 yr) in interdrainage settings within the Chihuahuan Desert and the High Plains in Texas. In addition, chloride concentrations were measured in soil water to characterize water movement at millennial time scales. The water potential monitoring data indicate that infiltrated water after wet periods is rapidly removed by evapotranspiration as vegetation productivity responds to increased soil moisture. Wetting fronts were restricted to the upper 0.3 to 0.8 m depth in different profiles. Vertical water potential profiles indicate that water potentials increase with depth indicating an upward driving force for water movement. Chloride profiles are typically bulge shaped and represent 10,000 to 15,000 yr of accumulation. Modeling of water potential and chloride profiles indicates that maintenance of low water potentials in the root zone by evapotranspiration can result in long-term drying of these profiles and the time scales represented by the chloride profiles suggest that this process has been ongoing for the last 10,000 to 15,000 yr since the Pleistocene. Xeric vegetation in these interdrainage settings is extremely effective in removing infiltrated water and has resulted in long-term drying of these profiles, precluding deep water percolation and groundwater recharge.

KEY WORDS: chloride, Ecology, groundwater recharge, Evapotranspiration