It was a great honor to attend a Symposium on Ecological Restoration and Efficient Utilization of Water Resources in Semi-arid Regions in Zhangjiakou, Hebei Province, China last week. I learned a lot about the issues of water shortage and contamination in Hebei (West and South-West of Beijing). The talks at the symposium presented the conflict between increasing water demand for agricultural and forestation, while the groundwater availability dropped dramatically over the last decades due to the ongoing land use changes. I presented how stable isotopes of water can help to assess the partitioning between green water (used by plants) and blue water (groundwater recharge), which are the grand challenges in semi-arid environments to ensure agriculture production and groundwater availability.

A field excursion to research centers investigating improved irrigation and fertilization practices showed current developments towards recommendations to the government and farmers in the Hebei province in order to mitigate further stress on the water supply.

I was further invited to visit the group of Prof. Shiqin Wang at the Center of Agricultural Resources Research of the Chinese Academy of Sciences in Shijiazhuang, Hebei, China. We visited one of her field sites in the Taihang Mountain and I enjoyed the discussion with her and her students.
The week-long trip allowed an in-depth insight into the current hydrological issues addressed in Chinese research, but also provided a unique experience of Chinese culture, drinks, and food. Thanks to Prof. Shiqin Wang, who made this possible! (Thanks to Shiqin and Yan-Jun for sharing their photos!)

Our study on measuring and modelling the isotopic composition of mobile and bulk soil water published in Vadose Zone Journal got featured in the CSA News of the Alliance of Crop, Soil and Environmental Science Societies. You can read the short abstract here.

Our study on water ages in the soil, transpiration, evaporation and recharge got published in Hydrology and Earth System Sciences after a lively discussion during the open peer-review process. We simulated how long the water travels through the compartments of the critical zone and also the median age of the water in each compartment. We found that the travel time distribution is not necessarily the same for evaporation and transpiration, as the roots access older water in deeper soil layers than the evaporation. Further, the travel time of the recharge flux is mainly driven by flushing events, when there is high recharge during winter (in Scotland) or during snow melt (in Canada and Sweden). Water ages are generally lower the higher the storage and increase with decrease in soil wetness. This is true for recharge and also evaporation and transpiration fluxes. We hope to contribute with this to the ongoing research on how the soil-plant interactions affect the water flow and transport in the upper critical zone. You can download the manuscript here.

I am happy to announce that I just started this week a two-year project on "Water age dynamics in a Mediterranean catchment and their ecohydrological implications in a changing environment" funded by the German Research Foundation (DFG).
I will work together with the team of the Surface Hydrology and Erosion Group of the Institute of Environmental Assessment and Water Research (IDAEA-CSIC) in Barcelona on their extensive data set gathered in the Vallcebre Research Catchments (an overview of the impressive research and data sets from the IDAEA group can be found here). We will use hydrometric and stable isotope data from various hydrological compartments (precipitation, stream, groundwater, soils, plants) to assess travel times across the catchment with latest modeling approaches to improve the understanding of storage and release of water in the highly seasonal environment of the headwater catchment contributing to the water supply of the Barcelona area. If you are interested what we will be doing in the coming two years, you can follow project updates on researchgate.

I look forward to organizing a session for the AGU Fall Meeting 2018 with Natalie Orlowski, Todd Dwason, and Stephen P Good on "Stable Isotopes in the Critical Zone: Methods, Applications and Process Interpretations".
If you use stable isotopes to study the Earth's Critical Zone, we would be happy to receive your abstract before 1st of August here.

The special section on "Stable isotope approaches in vadose zone research" in Vadose Zone Journal is complete and online as open access here, including our study on "Measuring and modelling stable isotopes of mobile and bulk soil water".

We compiled stable isotope data (2H and 18O) of bulk soil water at five long-term experimental catchments across a hydro-meteorological gradient in the northern latitudes (Figure 1). The comparison of the extensive data set, covering different landscape units at each catchment, showed that vegetation, topography and elevation affect the isotopic composition over time and soil depth. Soil water beneath conifers is more enriched in heavy isotopes than beneath heather or oak vegetation. Sampling sites closer to the stream are generally less variable in their stable isotopic composition than sites at gentle hillslopes. Isotopic fractionation due to soil evaporation was observed mainly in the top 10 to 30 cm and was mainly controlled by the precipitation amount while temperature (as proxy for evaporation) was less important and soil moisture did not influence the isotopic fractionation, as revealed by multiple linear regression. 
The study will be published (here) in a Special Issue on "Water in the Critical Zone" in Hydrological Processes. The work was funded by the ERC grant VeWa and you can find a presentation by Doerthe Tetzlaff about that project here.

The final version on the manuscript on "Measuring and Modeling Stable Isotopes of Mobile and Bulk Soil Water" is now online available and can be downloaded here.

I will be working for three months on pooling ideas we gathered during a workshop on "Water Ages in the Hydrological Cycle" funded by the Wassernetzwerk Baden-Württemberg last October. My main collaborator for this short project will be Christine Stumpp and Markus Weiler.

A study on water ages and travel times in the critical zone is now out in Hydrology and Earth System Sciences Discussion. We used in this study the SWIS model that was tested at different sites in the northern latitudes in a previous investigation. We tracked the infiltrated water through the soil profiles and in the evaporation, transpiration and recharge fluxes. This way, we could derive travel times (which show how long the water takes to leave the soil via evaporation, transpiration or recharge), and median water ages (to estimate the median age of water in soil storage or the evaporation, transpiration and recharge fluxes). Our results showed for each study site, that water ages of soil storage, evaporation, transpiration and recharge were inversely related to the storage volume of the critical zone: water ages generally decreased exponentially with increasing soil water storage. These findings on the 1-D soil profile support the "inverse storage effect" as recently discussed for the catchment and hillslope scales. You can download the manuscript here.