多同位素示踪阿拉善高原沙漠非饱和带剖面水分运动机理

The deserts on the Alashan Plateau are one important component of the global arid zone. Due to extremely dry with little rain in this region, water in the unsaturated zones is a critical factor limiting plant growth, desert pedogenesis and eolian sand activities. However, there are seldom studies on water movement in the unsaturated zones of this region. In this project, muti-isotopes and geochemical methods （18O,2H, 3H, 37Cl/35Cl, 36Cl/Cl, 87Sr/86Sr and Cl-）are used to study the following contents: (1) the amount of rainfall, water levels of groundwater and the feature of their isotopes; (2) isotopic variations of water in the unsaturated zones in time and space; (3) the source of water in the unsaturated zones, patterns and relative contributions of rainfall infiltration to groundwater; (4) the response of water in the unsaturated zones to rainfall, evaporation and groundwater; (5) the source of plant water and its influence on water in the unsaturated zones; (6) the recharge rate, the transit time and the recharge history of water movement in the unsaturated zones; (7) the simulation of isotopic hydrology in the unsaturated zones according to the above studies. The aim of this project is to illustrate the mechanism of water movement in the unsaturated zones of the Badain Jaran and Tengger deserts on the Alashan Plateau in order to complete the theories of isotopically hydrological cycles in arid deserts and to help the scientific guide to the use of water resource, ecosystem establishment and desertification protection.

阿拉善高原沙漠是全球干旱区的重要组成。由于干旱少雨，非饱和带剖面水分是制约该区植物生长、成壤强度及风沙运动的关键因子，但有关剖面水分运动的研究还很缺乏。本项目选择阿拉善高原巴丹吉林和腾格里沙漠作为研究区，选取典型的地下水-土壤-植物-大气连续体，综合应用多种同位素与地球化学方法（18O、2H、3H、37Cl/35Cl、36Cl/Cl、87Sr/86Sr及Cl-），查明降水水量、潜水水位及其同位素特征，剖析非饱和带剖面水分中的同位素组成变化规律，确定剖面水分来源及降水入渗并补给潜水的方式与分量，阐明剖面水分对降水、蒸发及潜水的响应机制，并探究植物水分来源及对剖面水分的影响，进一步计算剖面水分运动速率、滞留时间与重建其补给历史，集成研究建立同位素水文模拟模型，深入揭示非饱和带剖面水分运动机理，不仅丰富干旱区沙漠同位素水文循环理论，更有助于科学指导阿拉善高原水资源利用、生态恢复与防沙治沙。

阿拉善高原位于内蒙古西部，降水量少，蒸发量大，植被生长稀疏，生态环境恶劣。为了科学管理当地的水资源和高效恢复生态环境，掌握高原水分循环的科学知识非常必要。本项目把土壤水、地下水和大气降水纳入一个整体，着重查明了阿拉善高原沙漠大气降水同位素与化学组成变化规律，探讨地下水补给来源机制，阐明土壤水分、地下水与大气降水的内在关联，剖析沙丘剖面土壤水分运动机理。通过详细的研究获得了如下几点重要结果：（1）阿拉善高原大气降水同位素组成具有明显的季节性变化特征，其水汽主要在西风带和极地气流作用下从大西洋和北冰洋等地输送而来；（2）阿拉善高原沙漠地下水是由当地降水和雅布赖山降水侧向补给而来，其中，雅布赖山降水的贡献占主导地位；（3）沙丘剖面土壤水分同位素分馏在降水进入沙丘之前就已经形成了，剖面上部的水分主要受大气降水的影响，而剖面下部的水分受到地下水的制约；（4）大气降水入渗沙丘剖面并非像已有研究认为的那样慢，特别是大雨，可能入渗速度很快，成为土壤水和地下水的主要补给来源。这些重要的结果弥补了已有研究的不足，大大提升了对干旱区水分循环理论的深入认识。同时，这些新的认识有助于指导当地水资源的科学管理和脆弱的生态环境恢复，从而促进当地社会、经济与环境的协同和谐发展。