Stable isotopic evidences of surface - groundwater circulation in the Mountain - Desert - Oasis system, South Tianshan Mountains

Water demand consistently exceeds supply in many parts of the world, especially in the arid and semi-arid regions. As human water need is increasing worldwide, the growth of pressure on water resources and its sustainable development is in jeopardy. The Tarim River Basin, with a size of 1.02×10⁶ km², is the largest inland river basin in Central Asia. In this study, we implemented a stable isotope mass balance method to study isotopic characterization of the Tarim River Basin and to quantify recharge proportion between water bodies of typical regions. There are two aims of this study: (i) to investigate spatial and temporal variations of δD and δ¹⁸O of river water and their sources within the large-area of the Tarim River in northwestern China, and (ii) to evaluate the ratio of different water types in the river water from a high mountain area to the downstream region. Taken altogether, we expect that the results will provide insight for water resource and watershed management in the large inland river basin and similar watersheds of Central Asia. In this study, Seasonality in the isotopic composition of river water was evident, where water in the dry season was further affected by processes such as recycling of water vapor and secondary evaporation. The mountain area was recharged with snowmelt and precipitation, with the isotopic composition largely dependent on elevation. Ground waters in the mid and downstream regions were recharged by surface water directly. The contribution of ice-snowmelt water varied from 14.97% to 40.85%, and that of rain varied from 9.04% to 54.80%, while that of groundwater varied from 15.34% to 58.85%. Ice-snowmelt water was still the main contributor to baseflow, so the Hotan River and the Yarkand River are melt water-dependent rivers. Seasonal precipitation is the main supplying water source of baseflow in the Aksu River and the Kaidu River. The importance of ice-snowmelt in runoff is determined by climate sensitivity, and a warming and drying climate may impose significant changes in the hydrology of the Tarim River basin, which may then influence the reasonable utilization of limited water resources in the future.