[Assessing the "two water worlds" hypothesis by stable isotope method: Progress and prospect].

Area of Science:

• Soil science
• Hydrology
• Ecology

Background:

• The two water worlds (TWW) hypothesis posits two independent soil water pools: bound water for plants and mobile water for runoff/recharge.
• This contrasts with traditional models assuming complete soil water mixing and is crucial for developing new hydrological models.

Purpose of the Study:

• To review the research progress, discrimination methods, controversies, and future prospects of the TWW hypothesis.
• To highlight the current lack of clarity regarding the theoretical underpinnings and formation conditions of the TWW hypothesis, especially in China.

Main Methods:

• Evaluation of existing studies primarily relies on hydrogen and oxygen stable isotope (²H, ¹⁸O) techniques.
• Methods include direct comparison, precipitation intersection point, precipitation residual, and precipitation migration methods.

Main Results:

• Research shows three viewpoints on the TWW hypothesis: support, partial support, and rejection.
• Discrepancies in results are attributed to the representativeness of isotope samples and limitations of isotope technology.

Conclusions:

• Developing non-isotope-based methods is essential for future research.
• Clarifying the theoretical basis of the TWW hypothesis is critical.
• Future studies should integrate multi-disciplinary approaches, multi-scale assessments, and multi-factor analyses to understand the ecological hydrological coupling.