Evapotranspiration, Groundwater, and Unsaturated-Zone Data, Amargosa Desert, Nye County, Nevada, 2011-13

Abstract from SIR 2017-5079: This report documents methodology and results of a study to evaluate groundwater discharge by evapotranspiration (GWET) in sparsely vegetated areas of Amargosa Desert and improve understanding of hydrologic-continuum processes controlling groundwater discharge. Evapotranspiration and GWET rates were computed and characterized at three sites over 2 years using a combination of micrometeorological, unsaturated zone, and stable-isotope measurements. One site (Amargosa Flat Shallow [AFS]) was in a sparse and isolated area of saltgrass (Distichlis spicata) where the depth to groundwater was 3.8 meters (m). The second site (Amargosa Flat Deep [AFD]) was in a sparse cover of predominantly shadscale (Atriplex confertifolia) where the depth to groundwater was 5.3 m. The third site (Amargosa Desert Research Site [ADRS]), selected as a control site where GWET is assumed to be zero, was located in sparse vegetation dominated by creosote bush (Larrea tridentata) where the depth to groundwater was 110 m. Results indicated that capillary rise brought groundwater to within 0.9 m (at AFS) and 3 m (at AFD) of land surface, and that GWET rates were largely controlled by the slow but relatively persistent upward flow of water through the unsaturated zone in response to atmospheric-evaporative demands. Greater GWET at AFS (50 ± 20 millimeters per year [mm/yr]) than at AFD (16 ± 15 mm/yr) corresponded with its shallower depth to the capillary fringe and constantly higher soil-water content. The stable-isotope dataset for hydrogen (δ2H) and oxygen (δ18O) illustrated a broad range of plant-water-uptake scenarios. The AFS saltgrass and AFD shadscale responded to changing environmental conditions and their opportunistic water use included the time- and depth-variable uptake of unsaturated-zone water derived from a combination of groundwater and precipitation. These results can be used to estimate GWET in other areas of Amargosa Desert where hydrologic conditions are similar.SIR 2017-5079 会议摘要：本报告详述了一项研究的方法与成果，该研究旨在评估阿马戈萨沙漠（Amargosa Desert）稀疏植被区域的地下水蒸散发（groundwater discharge by evapotranspiration, GWET），并深化对调控地下水排泄的水文连续体过程的认知。 研究结合微气象学、非饱和带与稳定同位素测量手段，在3处站点开展了为期2年的监测，对蒸散发与GWET速率进行计算与特征分析。 第一处站点为阿马戈萨平原浅水区（Amargosa Flat Shallow, AFS），地处一片稀疏孤立的盐草（Distichlis spicata）分布区，地下水位埋深3.8米（m）。第二处站点为阿马戈萨平原深水区（Amargosa Flat Deep, AFD），以滨藜（Atriplex confertifolia）为优势种的稀疏植被覆盖区，地下水位埋深5.3米。第三处站点为阿马戈萨沙漠研究站（Amargosa Desert Research Site, ADRS），作为GWET假定为0的对照站点，分布以三齿拉瑞阿（Larrea tridentata）为优势种的稀疏植被，地下水位埋深达110米。 研究结果显示，毛细上升作用将地下水抬升至距地表0.9米（AFS站点）与3米（AFD站点）的位置，且GWET速率主要由大气蒸发需求驱动下，地下水经非饱和带缓慢且相对持续的向上流动过程所调控。AFS站点的GWET（50±20毫米/年[mm/yr]）高于AFD站点（16±15毫米/年），这与其更浅的毛细饱和带埋深以及持续更高的土壤含水量相契合。氢（δ²H）与氧（δ¹⁸O）稳定同位素数据集展现了多样化的植物吸水情景。AFS站点的盐草与AFD站点的滨藜会响应环境条件变化，其机会主义取水策略包含随时间与深度变化地吸收由地下水与降水共同补给的非饱和带水分。本研究成果可用于估算阿马戈萨沙漠内其他水文条件相似区域的GWET。