Assessing groundwater recharge and transpiration in a humid northern region dominated by snowmelt using vadose-zone dept
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Assessing groundwater recharge and transpiration in a humid northern region dominated by snowmelt using vadose-zone depth profiles Lamine Boumaiza 1 & Romain Chesnaux 1 & Julien Walter 1 & Christine Stumpp 2 Received: 20 December 2019 / Accepted: 17 June 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Profiles of the stable isotope ratios of pore water within the vadose zone provide fingerprints of the history of water percolation into a soil. These profiles, combined with profiles of the volumetric water content, can determine the timing and amount of water that has percolated during specific periods. This study aims to: (1) understand water percolation at two sites in Quebec (Canada) that experience thick snow coverage during the winter season; (2) calculate groundwater recharge rates using the peak-shift method; and (3) estimate the transpiration rate based on the water balance budget. A 7-m-deep borehole was drilled at two sites: one site is sparsely covered by vegetation (S1), while the second underlies a pine forest (S2). For all subsamples, δ18O and δ2H from the soil pore water were analyzed, volumetric water content of the cores was measured, and grain-size analyses to estimate the hydraulic properties were performed. For both boreholes, the winter–spring and summer–autumn periods were determined. Given the limited evapotranspiration occurring during the winter–spring period, recharge rates were high at both sites (71 and 75%), while the summer–autumn period had lower recharge rates of 63% (S1) and 41% (S2). A transpiration rate of 0.7 mm/day was estimated for the pine trees covering site S2. This study provides new field observations for estimating recharge based on water stable isotope profiles in a humid northern region dominated by snowmelt. Moreover, it confirms the accuracy of the peakshift method for assessing groundwater recharge and estimating transpiration. Keywords Groundwater recharge . Peak-shift method . Stable isotopes . Water flow . Canada
Introduction As the stable isotope ratios of precipitation are strongly correlated with air temperature, a distinct seasonal pattern of rainfall is found in temperate humid climates, containing a greater proportion of heavy isotopes during summer and a lower proportion of heavy isotopes in winter (Dansgaard 1964). Thoma et al. (1979) were the first to observe that the seasonal variations of hydrogen water stable isotopes (δ2H) present in rainfall are preserved in the unsaturated zone (Koeniger et al. 2016). Saxena (1987) successfully traced the vertical shift of soil moisture, observing a distinct
* Lamine Boumaiza [email protected] 1
Département des Sciences Appliquées, Université du Québec à Chicoutimi, Chicoutimi, Québec, Canada
2
Institute for Soil Physics and Rural Water Management, University of Natural Resources and Life Sciences, Vienna, Austria
seasonal variation between the lighter winter snowmelt water and the heavier summer rainfall water. Since then, the distinctive succession of peaks characteri
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