 Our study showing that subsurface water of the studied silty-loam soil in the Vallcebre research catchment did not mix well over the studied 8 month period is now published in Hydrology and Earth System Sciences.
The SURFACE HYDROLOGY AND EROSION GROUP at IDAEA-CSIC gathered an extensive data set of water in the soil (both mobile and bulk soil water), in a piezometer, rainfall, and streamflow. The fortnightly sampling frequency revealed that despite pronounced changes in the soil wetness, the water in smaller pores were of different isotopic composition than the water moving in bigger pores. Mobile water sampled with suction lysimeter (circles and blue frame in Figure) was more similar to summer rainfall, while bulk soil water (stars and green frame in Figure) was more similar to winter rainfall. Thus, there is water located in small soil pores, which does not mix well with newly infiltrating, indicating non-uniform water transport across the studied soil profile. We could explain the isotope pattern relating rainfall stable isotopes and soil moisture, which showed that smaller pores (soil is dry) get refilled with more isotopically depleted rainfall. These findings provide a mechanistic explanation for subsurface heterogeneity in stable isotope values, which is important for improving model realism of hydrological simulations or ecohydrological applications of isotopes.
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 We offer in 2019 for the third time a session on "Stable Isotopes in the Critical Zone: Methods, Applications, and Process Interpretations" at the AGU Fall Meeting. This year our convener team will be composed by Stephen P. Good, Natalie Orlowski and Scott T. Allen. Abstract submission is open from June 12th to July 31st.
Session description: Stable isotopes are powerful tools for tracing fluxes of water, carbon, and nutrients. They are increasingly used in various disciplines to better understand processes occurring in the soil-plant-atmosphere continuum. Furthermore, new methodological and technological developments have facilitated tracing isotopes at much finer scales, but also across larger domains. By enabling the tracing of exchanges across distinct landscape pools, stable isotopes support new interdisciplinary perspectives on critical zone processes. This session aims to address the current state of the art for methods, applications, and process interpretations using stable isotopes in the critical zone. Studies that cross disciplinary boundaries and reveal new process understanding are especially welcome. This session also encourages contributions that celebrate the AGU's Centennial, including reviews of historical data and the evolution of stable isotope tools within the critical zone, as well contributions that discuss the future direction and needs of the critical zone stable isotope community.  We are inviting applications for the new Black Forest Autumn School on "Water Ages in the Hydrological Cycle", which will be held at from October 27 to 31 in Freudenstadt, Germany. The Black Forest Autumn School will teach approaches,
methods and models to determine water fractions, water ages and transit times throughout the hydrological cycle and will foster inter-disciplinary discussions. Lectures and hands-on exercises including a small model intercomparison project will provide a stimulating learning environment. The lecturer team consists of Markus Weiler, Christine Stumpp, James Kirchner, Markus Hrachowitz, Paolo Benettin and me. The Autumn School is supported by the Water Research Network Baden-Württemberg. The course fee is 290 €, but free participation for young scientists from Baden-Württemberg. If you would like to attend, send a 1 page motivation letter and your CV to info@wassernetzwerk-bw.de by July 15 2019. More info on this flyer.  I wrote a blog post for the EGU HS blog that you can read here: https://blogs.egu.eu/divisions/hs/2019/05/22/everything-is-interaction-and-reciprocal/ and below is a list of literature on which this post was partly based and could provide further reading for the interested among you:
Originals
 Looking at the demographics of water in the critical zone. The literature in hydrological science on how long a rain drop takes to pass through the soil, may be taken up by trees, end up back in the atmosphere via evaporation, or recharge the groundwater and streams is ever growing (see graph below). In our accepted manuscript on "The demographics of water: A review of water ages in the critical zone", we provide an overview on the current developments and open questions in this vibrant field dealing with water ages to improve the understanding of flow paths. This manuscript evolved from a workshop on “Water Ages in the Hydrological Cycle” held in October 2017 in the Black Forest funded by the Wassernetzwerk Baden-Württemberg. Back then, we discussed for about three days our experiences, new thoughts and challenges in estimating water ages in the terrestrial water cycle.  Participants of the workshop on "Water Ages in the Hydrological Cycle". Discussions at this workshop initiated the review paper. Our interdisciplinary group of scientists brought together various aspects that appear to be relevant for a better understanding and would be worth looking into in the future. This review manuscript is the result of these discussions at the workshop and via emails afterwards. It has been a great experience to work with that many bright scientists and put different views based on different backgrounds together. The collaborative and supportive atmosphere within the group of co-authors were extremely motivating and a great example for the success of interdisciplinary work. Thanks to the Wassernetzwerk Baden-Württemberg and the DFG for the financial support to work on this manuscript. You can download the accepted manuscript here.  Annual numbers of publications (orange line) with either "Travel times" or "Transit times" or "Water age" or "Residence times") in their title or keywords published in the journals “Water Resources Research”, “Journal of Hydrology” or “Hydrological Processes”. Horizontal lines indicate the average values over the indicated decade. Numbers of publication are also given in relation to the total number of publications in the considered journals (blue line, given in %). (Figure is not part of the review manuscript.) We present in HESSD an extensive stable isotope data set gathered by the Surface Hydrology and Erosion group at IDAEA-CSIC, Barcelona. Our study sheds light on the hypothesis of “ecohydrological separation” that was stated in the seminal paper by Brooks et al. (2010) almost ten years ago. Their publication initiated many stable isotope (2H and 18O) studies in ecohydrology, tree physiology, and vadose zone hydrology. However, the mechanism of how two subsurface water pools of different isotopic compositions evolve and persist are not yet understood. This lack of understanding is partly due to insufficient sampling frequencies of isotope data in the field. We overcome this limitation by a unique sampling design gathering isotope data of mobile and bulk soil water, rainfall, groundwater, and stream water in a fortnightly frequency over 8 months. We further extended our study by four years using long-term stable isotope and soil moisture data to reveal that the seasonal dry down of the soil and the wetting up of the soil pores with isotopically distinct rainfall can explain the disjunct isotopic compositions of water that is either stored in the soil or routed quickly to the groundwater and streams. Our findings provide the scientific basis to refute the often-made assumption in environmental modelling that water is well mixed in the subsurface. We further provide suggestions on how to implement our findings in future modelling frame works, by accounting for pore scale variability of water transport.  I am happy to see the blog for the European Geosciences Union (EGU) Hydrological Sciences Section online. Together with Maria-Helena Ramos, Bettina Schaefli, Giulia Zuecco, and Wouter Berghuijs, I will organize this new platform for the hydrological sciences community. We aim for this blog to be driven by the EGU HS section and we thus welcome suggestions for blog posts and contributions from everyone interested. You have an idea? Then, please contact me and we will work on adding it to the list of future blog posts. Find more info about the motivation and scope of the blog here.  During my visit at the Center for Agricultural Resources Research in Shijiazhuang, Hebei last summer, I got involved in the work by master student, Meijia Zhu, who gathered an impressive hydrochemical data set in the Xiong’an New Area. I learned that this area will provide new housing for the ever growing region around the Chinese capital. However, the North China Plain, where these developments take place is characterized by a dramatic drop in the groundwater levels over the last decades due to its over consumption; mainly for agricultural use. Due to the water scarcity related to the groundwater mining, rivers, are running dry. To counter this development water gets regularly transferred from other basins (see Figure 4). Though, often, the river flow is dominated by sewage water from urban areas.  Figure 6. Spatial interpolation of groundwater depth (a), electrical conductivity (EC) (b), Cl− (c) and δ18O (d) of groundwater along the Fu River. The work lead by Meijia Zhu now shows that this sewage water is not only affecting the water quality of Lake Baiyangdian, largest freshwater lake, but it also aggravates the underlaying groundwater body. We see, that the Chloride and electrical conductivity increases along the groundwater underlying studied river that flows into the Lake Baiyangdian (see Figure 6). We used end-member mixing analysis to show the ratio groundwater recharge sourced from either rainfall, lake water, or river water (see Figure 9). The study shows clearly how the groundwater body is not only threatened by depletion, but that the combination of over use and sewage disposal into rivers affects the groundwater challenging the water supply of the new developing Xiong’an New Area.  Figure 9. d18O values versus Cl- concentrations of the groundwater and end-members. The mean values of Cl□ concentration and stable isotopes of the Fu River water in seasons without the influence of the precipitation and transferred water (samples collected in January 2018 and March 2018) were taken as values of one end-member that reflects sewage influence. The manuscript to this study is openly available here.
Zhu M, Wang S, Kong X, Zheng W, Feng W, Zhang X, Yuan R, Song X, Sprenger M (2019): Interaction of Surface Water and Groundwater Influenced by Groundwater Over-Extraction, Waste Water Discharge and Water Transfer in Xiong'an New Area, China, Water, 11(3), 539, doi: 10.3390/w11030539. We are welcoming contributions to a special issue in Hydrology and Earth System Sciences. The idea to this special issue arose out of successful conference sessions held at EGU and AGU. This special issue will bring together the vibrant ecohydrological community addressing a better understanding of hydrological processes taking place from the canopy to the root zone. Many of these dynamic interactions between vegetation and soil affecting water, isotope and solute fluxes are not yet well understood. The special issue should therefore further address open questions and new opportunities within the ecohydrological community regarding methodological developments such as the analysis of stable isotope, soil moisture, throughfall or solute dynamics. We keep the submission open for all submissions within its scope. The editors for this special issue are Natalie Orlowski, Matthias Sprenger, Josie Geris, Pilar Llorens, Lixin Wang, and Miriam Coenders-Gerrits. Please contact us in case you have questions regarding manuscript submissions.  Looking forward to the EGU General Assembly, where I will present the first time work I currently conduct with the Surface Hydrology and Erosion Group, Institute of Environmental Assessment and Water Research (IDAEA-CSIC), Barcelona, Spain. My analysis and interpretation of a stable isotope data set gathered by my colleagues from Barcelona will be briefly presented in a PICO session and I hope to welcome many peers at the screen afterwards for some discussion. I am sure there will be lots to talk about with this extensive and exciting data set from the Vallcebre catchment in the SE Pyrenees that shows distinct compositions in the mobile and bulk soil waters. Also Frencesc will present latest work from the long-term research catchment and he will focus on the young water fraction different compartments.
While both of these presentations will be on Tuesday, make sure to stay until Friday, as this the day when we will have the session on "Water, isotope and solute fluxes in the soil-plant-atmosphere interface: Investigations from the canopy to the root zone " (see earlier post below).
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