Karst aquifers, formed in soluble carbonate rocks (e.g., limestone and dolomite), serve as major freshwater sources globally. However, their inherent hydrogeological complexity, characterized by conduit-dominated flow, multi-porosity, and high heterogeneity, poses significant challenges for accurately delineating groundwater flow paths. While traditional hydrogeological methods, including physical, chemical, and microbiological techniques, provide valuable insights, they often fall short in fully capturing the intricate dynamics of karst systems. Over recent decades, the integration of multiple isotopic and hydrochemical tracers has emerged as a powerful approach to illuminate this complexity. This review synthesizes recent advances in utilizing stable isotopes, radiogenic isotopes, and major water chemistry to characterize karst hydrogeology. Integrating these complementary tracers enables a more comprehensive understanding of recharge sources, residence times, water-rock interactions, and end-member (e.g., surface runoff, snowmelt, stream water) mixing processes along groundwater flow paths. Potential applications from diverse karst terrains demonstrate how multi-tracer integration provides significantly enhanced resolution and reliability in characterizing groundwater flow paths. This review also addresses methodological challenges and outlines future research directions, emphasizing the importance of interdisciplinary approaches that combine isotopic methods with other complementary techniques for the sustainable management and protection of vulnerable karst water resources.
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