Ecohydrological partitioning of water at long-term experimental sites in Northern latitudes using stable isotopes

Understanding the ecohydrological partitioning of soil water into evaporation, transpiration, and drainage fluxes in northern latitudes is crucial to assess future environmental changes induced by a changing climate or land use. As part of the ERC-funded VeWa project, we analyzed the isotopic signatures in soil pore waters for 12 landscape units differing in soil types and plant cover. We conducted a multisite comparison with study locations in four long-term experimental catchments: The Bruntland Burn in Scotland, Krycklan in Sweden, Wolf Creek in Canada, and Dry Creek in the USA. Four to nine isotope samplings took place over one year at the different sites. The analysis for 2H and 18O in the pore water was done for >1300 soil samples either by cryogenic extraction (Dry Creek) or by the direct equilibration method (the other sites).The soil isotope inter-site comparison revealed that the pore water isotope signal was generally dampened compared to the precipitation input signal at the different sites. Additionally, the precipitation pattern and the distinct soil textural characteristics influenced the pore water isotope composition over the soil depth. We further saw an isotopic fractionation of the pore water in the top soil due to evaporation, which varied over space (between the sites) and time (sampling time in the year).Importantly, to foster our understanding of soil water partitioning, we relate the observed soil water isotope patterns to vegetation characteristics (including stable isotopes in the vegetation), atmospheric drivers, and unique long-term isotope data of precipitation and streamwater. We integrate our findings into modeling the dynamic interlinkages of soil water, evaporation and transpiration and provide examples for plot and catchment scale models. Thus, our multi-site comparison of soil water isotope observations provided new insights into the spatial variability of hydrological processes within and across several experimental catchments.