Root Water Uptake On the Edwards Aquifer Recharge ZoneKarst Terrain: Quantifying Evaluating Contributions of Shallow and Deep Roots.

Ash juniper is invading grasslands and savannas on the karst Edward Plateau, Texas, and is suspected of reducing groundwater recharge because of the belief that juniper roots exploit deeper and more stable sources of water than what are available to grasses. However, recent work suggests that water sources for juniper are shallow and quickly depleted. The objective of this study is to monitor water profiles and quantify contributions of shallow and deep roots in soil and epikarst to water uptake. The experimental site was a savanna with ~50% woody cover on the Edwards Plateau. The soil is a gravelly loam with a high percentage of chert fragments and slabs overlying fractured limestone at a depth of ~1.5 m. The research used neutron scattering and time domain reflectometry (TDR) to measure water content profiles to a depth of 1.6 m.  Access tubes and TDR probes were installed on a 25 m x 25 m grid, with a 5-m node spacing (total of 36 access tubes and TDR probes). Three-dimensional maps of changes in water content with time during drying cycles were used to identify regions of active water uptake, and estimate evapotranspiration (ET).  ET estimates from the water balance were compared with estimates obtained from eddy covariance.