Global Institute for Water Security and School of Environment and Sustainability, University of Saskatchewan, Saskatoon, Saskatchewan S7N 3H5, Canada.
Department of Geography, University of Calgary, Calgary, Alberta T2N IN4, Canada.
Nature. 2015 Sep 3;525(7567):91-4. doi: 10.1038/nature14983.
Current land surface models assume that groundwater, streamflow and plant transpiration are all sourced and mediated by the same well mixed water reservoir--the soil. However, recent work in Oregon and Mexico has shown evidence of ecohydrological separation, whereby different subsurface compartmentalized pools of water supply either plant transpiration fluxes or the combined fluxes of groundwater and streamflow. These findings have not yet been widely tested. Here we use hydrogen and oxygen isotopic data ((2)H/(1)H (δ(2)H) and (18)O/(16)O (δ(18)O)) from 47 globally distributed sites to show that ecohydrological separation is widespread across different biomes. Precipitation, stream water and groundwater from each site plot approximately along the δ(2)H/δ(18)O slope of local precipitation inputs. But soil and plant xylem waters extracted from the 47 sites all plot below the local stream water and groundwater on the meteoric water line, suggesting that plants use soil water that does not itself contribute to groundwater recharge or streamflow. Our results further show that, at 80% of the sites, the precipitation that supplies groundwater recharge and streamflow is different from the water that supplies parts of soil water recharge and plant transpiration. The ubiquity of subsurface water compartmentalization found here, and the segregation of storm types relative to hydrological and ecological fluxes, may be used to improve numerical simulations of runoff generation, stream water transit time and evaporation-transpiration partitioning. Future land surface model parameterizations should be closely examined for how vegetation, groundwater recharge and streamflow are assumed to be coupled.
当前的陆面模型假定地下水、河流流量和植物蒸腾都是由同一充分混合的储水库（土壤）提供和调节的。然而，俄勒冈州和墨西哥的最新研究表明存在生态水文学分离现象，即不同的地下分室化水体分别为植物蒸腾通量或地下水和河流流量的综合通量提供水源。这些发现尚未得到广泛验证。在这里，我们利用来自全球 47 个分布地点的氢和氧同位素数据（(2)H/(1)H (δ(2)H) 和 (18)O/(16)O (δ(18)O))，表明生态水文学分离现象广泛存在于不同的生物群落中。每个地点的降水、河流水和地下水都大致沿着当地降水输入的 δ(2)H/δ(18)O 斜率分布。但是，从 47 个地点提取的土壤和植物木质部水都落在当地河流水和地下水之下的大气水线上，这表明植物利用的土壤水本身不会补给地下水或形成河流流量。我们的结果进一步表明，在 80%的地点，补给地下水和河流流量的降水与补给部分土壤水和植物蒸腾的水不同。这里发现的地下水分室化普遍存在，以及相对于水文和生态通量的风暴类型的分离，可能被用来改进对径流量生成、河流水流传输时间和蒸发蒸腾分配的数值模拟。未来的陆面模型参数化应仔细检查植被、地下水补给和河流流量之间的耦合方式。
