Characteristics and environmental driving factors of water transformation in the Balaguer River watershed of Inner Mongolia steppe.

Inner Mongolian steppe is one of the ecological barriers in China. The variation of water resources is very important for the development of social-economy and the protection of eco-environment. We collected 254 water samples of precipitation, river, and shadow groundwater during wet-season and dry-season of 2018-2019 from Balaguer River watershed and meansured the physical-chemical indicators, δD and δO of water samples. The stable isotope technology, mathematical statistics, and the inverse distance weighting method were used to analyze the stable isotope composition, spatial-temporal variation, and impact factors. Moreover, the -excess and the isotopic mixing ratio formula were used to analyze the conversion characteristics of different water and to identify their environment driving variables. The results showed that δD and δO of precipitation, river and shallow groundwater were higher in wet season than in dry season. The driving factors of different water transformation in the watershed were air temperature, altitude, and groundwater depth. Altitude was significantly negatively correlated with river δD, and the δD and δO of groundwater. δD and δO of groundwater fluctuated significantly in the area with groundwater depth less than 10 m, but were stable in other areas. There was a positive correlation between precipitation δO and air temperature. The -excess in wet season was higher than that in dry season, with a decreasing distribution characteristic from southern to northern part in the study area. More than 50% river in upper stream came from precipitation, while more than half river water converted to groundwater, with different recharge-drainage relationships existed between surface water and groundwater in different river reaches.