Abstract
Use of stable water isotopes has become increasingly popular in quantifying water flow paths and travel times in hydrological systems using tracer‐aided modeling. In snow‐influenced catchments, snowmelt produces a traceable isotopic signal, which differs from original snowfall isotopic composition because of isotopic fractionation in the snowpack. These fractionation processes in snow are relatively well understood, but representing their spatiotemporal variability in tracer‐aided studies remains a challenge. We present a novel, parsimonious modeling method to account for the snowpack isotope fractionation and estimate isotope ratios in snowmelt water in a fully spatially distributed manner. Our model introduces two calibration parameters that alone account for the isotopic fractionation caused by sublimation from interception and ground snow storage, and snowmelt fractionation progressively enriching the snowmelt runoff. The isotope routines are linked to a generic process‐based snow interception‐accumulation‐melt model facilitating simulation of spatially distributed snowmelt runoff. We use a synthetic modeling experiment to demonstrate the functionality of the model algorithms in different landscape locations and under different canopy characteristics. We also provide a proof‐of‐concept model test and successfully reproduce isotopic ratios in snowmelt runoff sampled with snowmelt lysimeters in two long‐term experimental catchment with contrasting winter conditions. To our knowledge, the method is the first such tool to allow estimation of the spatially distributed nature of isotopic fractionation in snowpacks and the resulting isotope ratios in snowmelt runoff. The method can thus provide a useful tool for tracer‐aided modeling to better understand the integrated nature of flow, mixing, and transport processes in snow‐influenced catchments.
Highlights
Stable water isotopes are useful and increasingly utilized tools for inferring water flow paths and travel times in hydrological systems [Kirchner, 2006; Birkel and Soulsby, 2015]
The isotopic composition of precipitation in the solid phase is typically depleted in heavy water isotopes (18O and 2H) compared to the mean annual signature due to colder temperatures during vapor condensation processes [Moser and Stichler, 1974], which leads to a situation where the accumulated snowpack and eventual snowmelt runoff is isotopically depleted with respect to the rest of the hydrological system
Though valuable work has been done in understanding snowpack isotope dynamics in snow-influenced northern catchments, the northern region is still underrepresented in the hydrological literature [Tetzlaff et al, 2015]
Summary
Stable water isotopes are useful and increasingly utilized tools for inferring water flow paths and travel times in hydrological systems [Kirchner, 2006; Birkel and Soulsby, 2015]. Being able to predict the evolution of snowpack and snowmelt isotope dynamics is a prerequisite to using traceraided modeling approaches in affected catchments [Lyon et al, 2010; Peralta-Tapia et al, 2016]. Such models are increasingly used for assessing mixing processes, storage dynamics, and travel times in a wide range of catchments [Birkel and Soulsby, 2015] as analysis of isotopic tracers is rapidly becoming more accessible [Berman et al, 2009]
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