Determination of spatiotemporal variability of tree water uptake using stable isotopes (δ¹⁸O, δ²H) in an alluvial system supplied by a high‐altitude watershed, Pfyn forest, Switzerland

Abstract

International audienceSources of water use by 10 alluvial trees in various hydrogeological and ecological situations at the Pfyn forest (Wallis canton, Switzerland) were assessed by analysing 18O and 2H isotopes of precipitation, soil water at different depths, surface water, groundwater and xylem sap. The soil water line in a δ18O versus δ2H diagram shows evidence of kinetic fractionation related to evaporation. The tree water line is close to the soil trend; however, an additional enrichment may occur and could be related to xylem–phloem communication under water stress. At sites where the water table was at least 2 m below the ground surface, isotopic temporal variability of soils and trees was strongly linked with seasonal variation of soil water content. When soil water content was low and water table shallow, trees used both soil water and groundwater. When soil water content was high, this source was usually the dominant source for transpiration. In addition, some ecological strategies, reproduction or growth competition, could explain shifts in the utilization of different water sources, for example, from soil water to a mix of soil water and groundwater. At one site where soil water and groundwater were abundant throughout the year (next to the river course), neighbouring trees permanently used distinct water sources. This is consistent with a strategy of competition limitation, which would favour bank colonization. These results provide insight into the ecohydrological functioning of this system and will aid future management responses to both local and climate changes

Soil water stable isotopes reveal evaporation dynamics at the soil–plant–atmosphere interface of the critical zone

“…The direct-equilibration method -as a potential alternative analysis method -we applied in our study was so far usually limited to study percolation processes (e.g., Garvelmann et al, 2012;Mueller et al, 2014;Sprenger et al, 2016a). To our knowledge, only Bertrand et al (2012) used the directequilibration method to study the water use by plant water use and the influence of evaporation fractionation, but they bulked the soil data of the upper 20 cm.…”

Exploring water cycle dynamics by sampling multiple stable water isotope pools in a developed landscape in Germany

“…The application of stable water isotopes as natural tracers in combination with hydrodynamic methods has been proven to be a valuable tool for studying the origin and formation of recharged water as well as the interrelationship between surface water and groundwater (Blasch and Bryson, 2007), partitioning evaporation and transpiration (Wang and Yakir, 2000), and mixing processes between various water sources (Clark and Fritz, 1997c). Particularly in catchment hydrology, stable water isotopes play a major role since they can be utilized for hydrograph separations (Buttle, 2006), to calculate the mean transit time (McGuire and McDonnell, 2006), to investigate water flow paths (Barthold et al, 2011), or to improve hydrological model simulations .…”

“…Once soil water reaches the saturated zone, this isotope information is finally transferred to the groundwater (Song et al, 2011). Soil water can therefore be seen as a link between precipitation and groundwater, and the dynamics of isotopic composition in soil water are indicative of the processes of precipitation infiltration, evaporation of soil water, and recharge to groundwater (Blasch and Bryson, 2007;Song et al, 2011).…”

Simulation of Water Use Dynamics by Salix Bush in a Semiarid Shallow Groundwater Area of the Chinese Erdos Plateau

“…Water use of the investigated bush vegetation system may involve both the competition and coordination mechanism referring to the bush ecological consistent as described in section 2.1. Moreover, Specific ecological features could also impact water-use strategies as point by Bertrand, et al [51]. Therefore, these vegetation water use strategies should be taken into account in further modeling efforts.…”