Stable isotope tracing the transformation dynamics of diverse water bodies in the Manas River Basin, Northwest China

The arid region of Northwest China is characterized by a typical continental climate with extremely limited water resources. To elucidate the transformation relationships among different water bodies in arid regions, samples of precipitation, surface water, soil water, and groundwater were collected from the Manas River Basin (MRB). This study delineated the spatiotemporal variation characteristics of stable isotopic composition of waters, and employed the MeteoInfo and MixSIAR models to elucidate the origins and transformation dynamics among the various water bodies in the MRB. The isotopic composition of precipitation exhibited significant seasonal variations, with depletion in winter and enrichment in summer. The smaller slope and intercept of the local meteoric water line relative to the global meteoric water line suggest a substantial sub-cloud evaporation effect. Surface and soil water isotopes gradually enriched from mountainous to desert regions in the MRB, inversely to those in groundwater. The conversions between groundwater and surface water predominantly occur in mountainous areas in the MRB, with an average exchange rate of 85%, while water transitions from oases to deserts are mainly driven by upstream processes. These findings enhance our understanding of water cycles in arid regions and offer guidance for sustainable water resource management strategies in the MRB.