Collaborative Research: WCR: Ecohydrology of semiarid woodlands: Role of woody plants in the water cycle

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0233584SternExtensive areas of semiarid grasslands and savannas have been converted into shrublands. There is a common, but untested, assumption that reducing shrub cover will have tangible and large-scale effects on streamflow and ground water recharge. Our study area is the Edwards Plateau of Texas, where coverage by juniper is extensive and hillslopes are composed of highly permeable and fractured limestone. Our research will answer basic questions about flow processes at multiple scales on these limestone hillslopes and better define how much, if any, of an increased water yield could result from shrub control. Large plot (3 m wide, 12 m long) rainfall simulation will be applied above the tree canopy to develop an understanding of water fluxes for a number of rainfall regimes. During a simulation event, we will continuously monitor overland flow, lateral subsurface flow, canopy interception, soil water, and transpiration. Three plot locations will be selected for simulation experiments: one on a steep rocky hillslope, one on flatter slopes with deeper soils, and a third site above a cavern. The cavern site is especially significant because we should be able to obtain a good estimate of recharge rates. In addition, a series of isotopic studies at the hillslope, catchment and watershed scale will be conducted with the goals of (1) differentiating soil water loss via evaporation versus transpiration (2) conducting hydrograph separation using naturally occurring strontium (Sr) and O isotopes and trace element concentrations and ratios (Sr/Ca and Mg/Ca), and (3) determining shrub water use of rainfall, surficial soil water, and deep storage, both seasonally and spatially. The proposed study is a highly interdisciplinary examination and promises to be the most comprehensive examination of the ecohydrology of semiarid scrublands.