Using storage selection functions to assess mixing patterns and water ages of soil water, evaporation and transpiration

Aaron A. Smith*, Doerthe Tetzlaff, Chris Soulsby

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)


Understanding flow and transport processes in the critical zone relies heavily on characterising the interactions between evaporation and vegetation uptake of soil water; however, the magnitude, sources, and ages of these water fluxes are rarely well-constrained. We adapted the StorAge Selection (SAS) function framework to estimate the residence time of stored water, and transit times of eco-hydrologic fluxes, at multiple soil depths in typical soil-vegetation units in the humid, energy-limited Scottish Highlands. Modelling water and stable isotope fluxes within the soil-vegetation units indicated that rapid movement of young water through the soils occurred at both sites, creating relatively stable water residence times in the soils with depth and time. Estimation of the evaporation profile had limited temporal variability with a high preference for near-surface water (0 – 5 cm soil depth, long-term mean age: 50 – 65 days) due to relatively frequent precipitation. Root uptake profiles revealed higher temporal variability, favouring deeper water (5 – 15 cm) during drier periods and near-surface (0 – 5 cm) during wet periods (long-term mean age: 6 – 15 days older than evaporation). The model structure provides a tool to help constrain water storage–flux–age interactions in the upper part of the critical zone and understand how soil–vegetation systems influence groundwater recharge and catchment-scale hydrology.

Original languageEnglish
Article number103586
Number of pages17
JournalAdvances in Water Resources
Early online date15 May 2020
Publication statusPublished - Jul 2020

Bibliographical note

We would like to thank the European Research Council (ERC, project GA 335910 VeWa) for funding the project. We would like to thank Matthias Sprenger, Matt Kohn, Hailong Wang, Jonathan Dick and Josie Geris for sample collection and/or isotope analysis. We also thank detailed the detailed and constructive criticisms of the five reviewers that have helped improve the paper. The data used will be available on the University of Aberdeen Public Research Portal (PURE).


  • Ecohydrological separation
  • Root uptake source
  • Soil water ages
  • Storage selection


Dive into the research topics of 'Using storage selection functions to assess mixing patterns and water ages of soil water, evaporation and transpiration'. Together they form a unique fingerprint.

Cite this