The two water worlds hypothesis: Addressing multiple working hypotheses and proposing a way forward

Z. Carter Berry (Corresponding Author), Jaivime Evaristo, Georgianne Moore, María Poca, Kathy Steppe, Lucile Verrot, Heidi Asbjornsen, Laura S. Borma, Mario Bretfeld, Pedro Hervé-Fernández, Mark Seyfried, Luitgard Schwendenmann, Katherine Sinacore, Lien De Wispelaere, Jeffrey McDonnell

Research output: Contribution to journalArticlepeer-review

99 Citations (Scopus)


Recent studies using water isotopes have shown that trees and streams appear to return distinct water pools to the hydrosphere. Cryogenically extracted plant and soil water isotopic signatures diverge from the meteoric water lines, suggesting that plants would preferentially use bound soil water, while mobile soil water that infiltrates the soil recharges groundwater and feeds streamflow all plots on meteoric water lines. These findings have been described under the “two water worlds” (TWW) hypothesis. In spite of growing evidence for the TWW hypothesis, several questions remain unsolved within the scope of this framework. Here, we address the TWW as a null hypothesis and further assess the following: (a) the theoretical biophysical feasibility for two distinct water pools to exist, (b) plant and soil processes that could explain the different isotopic composition between the two water pools, and (c) methodological issues that could explain the divergent isotopic signatures. Moreover, we propose a way forward under the framework of the TWW hypothesis, proposing alternative perspectives and explanations, experiments to further test them, and methodological advances that could help illuminate this quest. We further highlight the need to improve our sampling resolution of plants and soils across time and space. We ultimately propose a set of key priorities for future research to improve our understanding of the ecohydrological processes controlling water flows through the soil–plant-atmosphere continuum.
Original languageEnglish
Article numbere1843
Issue number3
Early online date2 Mar 2017
Publication statusPublished - Apr 2018

Bibliographical note

We thank the AGU Chapman Conference on the Emerging Issues in Tropical Ecohydrology that took place in June, 2016 in Cuenca, Ecuador. Many of the ideas for this synthesis were developed during conversations there. We particularly would like to thank Brad Wilcox for organizing the conference and encouraging breakout discussions. Z.C.B., M.P., M.B., L.D.W., H.A., and K.S. (Katherine Sinacore) specifically acknowledge NSF for awarding a travel grant for attending the conference. P.H-F. acknowledges Programa de Personal Avanzado CONICYT, Becas Chile; and BOF (Bijzonder Onderzoeksfonds) for funding PhD studies. LV was supported by the Swedish University strategic environmental research program Ekoklim and the Swedish Research Council Formas (project 2012-790) and would also like to acknowledge the British National Environment Research Council (grant NE/N007611/1).


  • bulk soil water
  • ecohydrological separation
  • preferential flow
  • stable isotopes
  • two-domain flow


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