Use of stable isotope signals from tree rings as proxy for tracing the combined effects of climate change and hydropower on glacier-derived water resources in the Turtmänna river catchment, Switzerland

Stable isotope analyses (δ¹⁸O, δ²H) combined with the tree-ring dating have enormous potential for tracing freshwater resource availability under changing climate and in the context of the impacts of other human activities. This study focusses on the isotopic composition of tree-rings in combination with an anatomical analysis of the European Larch (Larix Decidua) species from different upstream and downstream sites along the Turtmänna river in south-western Switzerland. The results show distinctive patterns of year-to-year tree-ring growth from their constructed chronology dated back to 1851 (i.e. a 170-year record). A trend of a decreasing growth was noted over the last two decades. Decreasing growth was correlated (r = 0.50) with a decrease in precipitation and an increase in temperature (r = 0.30) during the growing season (between June and October) of previous and current years. The isotopic analysis shows a depletion in ¹⁸O in the trees fed by glacial meltwater close to the river as compared to the trees fed by precipitation distal to the river. Given the changes in climate, trees closer to the river are becoming more dependent on river-derived water, which in turn is sourced from melting glaciers. This hence has important consequences for the hydropower generation and water availability.