What Is the Age of Transpiring Fluxes? Exploring the Impact of Vegetation on Water and Solute Mass Balance

Abstract:

The problem of streamflow age has received increased interest in watershed studies, particularly where surface waters have been monitored to provide accurate measures of mass fluxes released by catchments. Discharge, however, is just one of the two main catchment exits and evapotranspiration can easily account for a major part of the water balance, especially during the warm seasons. While a large body of literature deals with the travel time distributions of discharge waters, few studies explicitly addressed the problem of the age of evapotranspiration and its impact on the catchment-scale mass balance. Several modeling tools can be used to hypothesize how plants remove water of different ages from the catchment storage, but the difficulty of collecting representative samples is still a challenge to the validation of such hypotheses. Here, we illustrate different modeling assumptions on the “age selection” mechanisms that may be expected from vegetation, and we present experimental results from a large vegetated lysimeter.