The least understood component of the hydrologic cycle in arid environments is ground water recharge, which is controlled by climate, soils, and vegetation. Lysimeter data support the hypothesis that ground water recharge in arid regions may be more common than previously thought, but high concentration of chloride in the root zone and upward water potential gradients lead to the opposite hypothesis that desert vadose zone experience negligible recharge.
These two contradictory recharge hypotheses may be conciliated with each other by recognizing different recharge mechanisms: (i) diffuse recharge; (ii) localized recharge in local depressions; (iii) preferential pathway flow. The general objective of this proposal is to test the hypothesis that on t he La Mesa and Las Canas surfaces in New Mexico locations with negligible recharge resulting from diffuse recharge mechanisms are intermixed with spots that produce considerable recharge caused by localized recharge and preferential flow.
The soils on the La Mesa and La Canas surfaces are underlain by an indurated calcic horizon, which is considered impermeable for soil water. However, an important feature of this horizon is the presence of pipes, which are filled with permeable soil materials and, thus may act as water conduits during periods with sufficient precipitation. If our research hypothesis is correct, low chloride concentrations will be found inside the pipes and high ones outside the pipes. The acceptance or rejection of the research hypothesis has important implications for water supply and for waste disposal in arid soils that are underlain by indurated calcic horizons.