Tracer model-based quantitative separation of precipitation and
permafrost waters used for evapotranspiration in a boreal forest
Abstract
Arctic precipitation (PG) that occurs as rainfall (Pr) or snowfall (Ps)
depending on the prevailing climatic conditions results in seasonally
specific hydrological events. Climate change can affect the PG- and
permafrost-originated water (Pi) regimes, resulting in change to
ecohydrological processes. However, the relative influences of source
waters (i.e., Pr, Ps, and Pi) on terrestrial hydrological processes have
not yet been fully established. Here, we report the development and
implementation of a numerical water tracer model designed to quantify
changes in the storages and fluxes of the source waters and the hydrogen
and oxygen isotopic tracers associated with hydrometeorological events.
The presented tracer model was used to illustrate the spatiotemporal
variability of the tracers in the surface–subsurface system of a
deciduous needleleaf boreal forest, and to separate the contribution
rates of the tracer waters to evapotranspiration (ET). Although Ps
accounted for 14%–40% of ET and the subcomponents, the contribution
rates to soil evaporation and transpiration were significant only during
the spring season. The major source water for soil moisture was Pr,
which accounted for 80.1% of ET and showed an increasing trend.
Additionally, Pr also accounted for 85.7% of transpiration. Under the
present conditions of warming permafrost, Pi demonstrated negligibly low
impact on ET. The tracer model was shown capable of quantifying the
contribution rates of tracer waters to ET, highlighting the advantages
of the tracer model for similar quantitative separation regarding future
climate change.