Abstract
<p><strong>Abstract.</strong> The aim of this study was to analyse and predict the mean stable water isotopic composition of the snow cover at specific geographic locations and altitudes. In addition, the dependence of the isotopic composition of the entire snow cover on altitude was analysed. Snow in four Swiss catchments was sampled at the end of the accumulation period in April 2010 and a second time during snowmelt in May 2010 and analysed for stable isotope composition of <sup>2</sup>H and <sup>18</sup>O. The sampling was conducted at both south-facing and north-facing slopes at elevation differences of 100 m, for a total altitude difference of approximately 1000 m. The observed variability of isotopic composition of the snow cover was analysed with stepwise multiple linear regression models. The analysis indicated that there is only a limited altitude effect on the isotopic composition when considering all samples. This is due to the high variability of the isotopic composition of the precipitation during the winter months and, in particular in the case of south-facing slopes, an enrichment of heavy isotopes due to intermittent melting processes. This enrichment effect could clearly be observed in the samples which were taken later in the year. A small altitudinal gradient of the isotopic composition could only be observed at some north-facing slopes. However, the dependence of snow depth and the day of the year were significant predictor variables in all models. This study indicates the necessity to further study the variability of water isotopes in the snow cover to increase prediction for isotopic composition of snowmelt and hence increase model performance of residence time models for alpine areas in order to better understand the accumulation processes and the sources of water in the snow cover of high mountains.</p>
Highlights
For more than 40 yr the stable water isotopes 18O and 2H have been used to determine hydrological pathways and processes in catchment hydrology (McDonnell, 2003)
We could prove the hypothesis that additional factors like the deviation of snow depth from the expected value due to altitude and the day of the year influence the variation of stable water isotopes in snow in space and time
These variables may serve as additional important predictors to altitude to predict the spatial and temporal variability of stable water isotopes in the entire snowpack
Summary
For more than 40 yr the stable water isotopes 18O and 2H have been used to determine hydrological pathways and processes in catchment hydrology (McDonnell, 2003). Due to their conservative nature in the water cycle, the relative simple sampling and nowadays cheaper and faster measurement technique, they are a commonly used tracer to determine the mean residence time of water in a catchment (Vitvar et al, 2007). Isotope fractionation processes during the ablation period are still poorly understood (Unnikrishna et al, 2002). A detailed knowledge of the isotopic composition of snow and snowmelt water can help us understand the snowmelt contribution to streamflow and/or the residence time of snowmelt in a catchment (e.g. Shanley et al, 2002; Schelker et al, 2011)
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