ECOHYDROLOGICAL AND HYDROMETEOROLOGICAL CONTROLS ON SOIL MOISTURE FLUXES IN ARID VADOSE ZONES

Previous research has identified ecohydrological factors as possibly being crucial components in determining the hydrological characteristics of deep arid vadose zones. This research also demonstrated that easily measurable vadose zone properties are a key to understanding these ecohydrological factors. The objective of present research is to determine the relative degree that ecology and climate influence the hydrodynamics of the underlying vadose zone. If ecology is the more influential factor in determining the vadose zone moisture regime, then a readily observable surface feature, vegetation, could be used to determine the underlying vadose zone moisture fluxes of the area and extensive drilling may not be necessary.

To determine the vadose zone moisture fluxes, eleven, five-to-ten-meter deep boreholes were drilled under ponderosa pine, juniper, grassland and creosote communities along a transect in Socorro County, New Mexico. The hydrometeorological conditions of this transect were quantified by means of the aridity index, equal to the average annual potential evaporation divided by the average annual precipitation. The aridity index decreases gradually along the transect, from east to west. This transect also contains the four ecological communities of interest. All borehole profiles were tested for water potential, water content, chloride content, and particle size to determine the moisture fluxes of the profiles.

Preliminary results demonstrate that while the data do vary within the vegetational communities, there are systematic differences between the vegetational communities tested. The data for the creosote sites demonstrates that there are no downward liquid fluxes past the root zone and thus no groundwater recharge. The data for the grass and juniper sites show that there are periodic, downward liquid fluxes through the vadose zone. The ponderosa pine data also shows periodic, downward liquid fluxes, but of a greater magnitude and occurrence than in the grass and juniper sites. Therefore, the available data support the original hypothesis that ecohydrological factors are a crucial component in determining the underlying deep vadose zone moisture fluxes in arid areas.