Using storage selection functions to assess mixing patterns and water ages of soil water, evaporation and transpiration. (July 2020)

• Record Type: Journal Article
• Authors: Smith, Aaron A; Tetzlaff, Doerthe; Soulsby, Chris
• Is Part Of: Advances in water resources. Volume 141(2020)
• Publication Date: 2020-07
• Subjects: Storage selection -- Ecohydrological separation -- Soil water ages -- Root uptake source; Hydrology -- Periodicals; Hydrodynamics -- Periodicals; Hydraulic engineering -- Periodicals; 551.48
• DOI: 10.1016/j.advwatres.2020.103586
• Languages: English
• ISSNs: 0309-1708

Abstract

Highlights: A modification of storage selection to include multiple soil water storages. Preference of young water to percolate through the soils under all wetness conditions. Higher affinity of near surface root-uptake during high soil moisture conditions. Evaporation and root- water ages are dependant on soil water ages near the surface. Abstract: 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.