The ICDP-funded Bushveld Drilling Project (BVDP) aims to generate a continuous vertical stratigraphic sequence of the mineral and resources-rich Bushveld Igneous Complex (BIC) in South Africa. Within this framework, a specific focus is directed towards gathering water-related data, aimed at enhancing the understanding of deep groundwater systems in relation to water and energy security. The present project complements the already ongoing and funded collaborative activities between the Hydrogeology group of UniBas, the main partner's group at University of the Free State, and the BVDP, via the addition of state-of-the-art measurements of radio-noble gases dissolved in water. The determination of the radio-noble gas isotope concentrations of ³⁹Ar, ³⁷Ar, ⁸⁵Kr, and ⁸¹Kr, alongside the already planned analyses of classic environmental tracers [i.e., stable water isotopes (∂¹⁸O, ∂²H), atmospheric noble gas concentrations (He, Ar, Kr, Xe), and other ratio isotopes (³H,³He, and ⁴He)] will allow the characterization (i) of the residence times and flow dynamics of the suspected hundreds-of-thousands- to millions-of-years old deep groundwater, which in turn enables the assessment of the spatial extents and hydraulic properties of the different lithological units in the BIC, (ii) of the origins of suspected large amounts of dissolved CH₄, which in turn enables assessment of the potential for using CH₄ from the BIC for sustainable energy production, and (iii) enable estimating the quantity, quality, and vulnerability of groundwater and therefore the suitability for using it as a drinking water source.

80% of Switzerland's drinking water is originating from groundwater. Climate change-induced droughts and increased demand for irrigation put groundwater under considerable pressure and cause widespread concern. In 2021, two popular initiatives were launched to protect groundwater and 2 parliamentary motions concerning groundwater were accepted in 2022/23. Now, for more than 3000 wells capture zones have to be delineated until 2035, and 4000km of rivers have to be restored within the next 70 years. Groundwater modelling plays an important role in tackling these challenges. However, the robustness of the current modelling practice is undermined by the poor characterisation of the subsurface, the computational challenges to jointly simulate surface- and groundwater and by the large resulting uncertainties. Consequently, stakeholders have to deal with complex issues but cannot fully exploit the potential of modelling to help them make relevant decisions.

In this project, we are addressing these shortcomings by (1) Employing cutting-edge mass-spectrometry technology to expand the available tracer methods with non-toxic gas tracers injected into the subsurface. This will greatly expand the spatial and temporal scales of available tracer methods and open new pathways to subsurface characterisation. (2) Building on the latest generation of integrated surface-subsurface hydrological models (ISSHM). This will allow joint consideration of the surface, the subsurface, and the operational infrastructure. Through the direct simulation of tracers, the model calibration is also far more robust and unique. (3) Providing the technological and computational means for real-time data assimilation in ISSHMs. This will guarantee that the model is always close to the real system state and thus can be continuously used to support operational decision-making. We have demonstrated the technical feasibility of all of these developments in our previous work.

This BRIDGE Discover project allows us to move this fundamental research to an operational level by collaborating among the three institutions through 12 coordinated work packages. In close collaboration with the relevant stakeholders, we develop and assess the efficiency of our hydrogeological service for two pilot studies: one to increase the efficiency of irrigation for agriculture, and the second one to predict the influence of a renaturation on well capture zones.

Mountainous countries like Switzerland are overproportionally affected by climate change, with temperature rise and increasing weather extremes such as heat waves, droughts, and torrential rainfalls already being more pronounced than elsewhere. Under these circumstances, water supply is becoming a major challenge for agriculture, be it for crop production or animal husbandry. In addition, water in mountain communities becomes increasingly scarce during summer months. This is where the Swiss Federal Office of Agriculture FOAG-funded "Slow Water" project comes in: In 3 hydrologically and geographically distinct pilot regions of Switzerland, farm-specific, catchment-related water retention strategies are developed together with municipalities and farmers in a co-creative process, and their impacts on increased water availability and decreased streamflow extremes assessed. The Slow Water project consortium consists of the Hydrogeology and the Global and Regional Land-Use Change groups of University of Basel, the regional authorities of the Cantons of Basel-Landschaft and Luzern, municipalities, farming associations and the private sector.

Humanity has reached a point where the capacity to live without irreversibly compromising Earth’s resources is questioned. Since the 1980s, both Earth’s population and global food production have been constantly increasing. To face the challenges of increasing food and water demand, agricultural production efficiency must be improved. Initiatives like the UN Sustainable Development Goals (SDGs) describe major challenges for clean water and food production. Accordingly, food production and access to clean water must be a priority in the context of sustainable development. To tackle these important challenges to sustainable development, the present project will build on a combination of agricultural field and integrated hydrological modelling experiments. The knowledge obtained in the field and modelling experiments will be ultimately combined to enable the creation of a prototype near-real time decision support tool for sustainable and resilient management of nitrogen fertilization.

In Poland, cereal production is a major component of the national economy. Even though fertilizer use has been restricted since 2017, in 2020 the Polish government still reported a significant trend of increasing nitrogen concentrations in water bodies. Climate change makes agricultural production even more vulnerable and challenging, pushing farmers to overfertilization. Given the fact that 30% of Polish agricultural soils consist of soils highly prone to fertilizer leaching, it comes as no surprise that excessive nutrient loadings are still widely observed. Due to its high mobility, the most applied agricultural fertilizer Nitrogen (N) is the most prone to leaching, and as a result, N (primarily in the form of nitrate) is by far the most widely observed agricultural contaminant in water bodies worldwide, including in Poland and Switzerland.

To tackle these important challenges to sustainable development, the project will build on a combination of field and modelling experiments. The Swiss project partner will focus on the integrated simulation of hydrological fluxes, crop dynamics and nitrogen-cycling. The Polish project partner will focus its research on field experiments in agricultural fields and in the university's outdoor agricultural laboratory. The knowledge obtained in the field and modelling experiments will be ultimately combined to enable the creation of a prototype near-real time decision support tool for sustainable and resilient management of nitrogen fertilization.

The broad focus of this research project is the improvement of the conceptual and quantitative understanding of surface water-groundwater interactions via state-of-the-art tritium measurement techniques and integrated surface-subsurface hydrological modelling. The specific goal is the development of a dissolved gases and water stable and tritium isotopes based method for the continuous monitoring of managed aquifer recharge (MAR) systems, which are considered the most important mitigation measures against the negative impacts of climate change on water availability. The field site is Switzerland's largest managed aquifer recharge (MAR) site Hardwald in Muttenz, Basel. Continuous analysis of the spatial and temporal distribution of tritium in the river Rhine and in the groundwater wellfield is achieved with the deployment of portable mass spectrometers for dissolved gas analyses and automated sampling devices for the sampling for water for isotopic analyses. In addition, within the framework of the project a new state-of-the-art tritium enrichment line is being built within Eawag's environmental tracer laboratory. The new enrichment line is combining recent methodological developments of IAEA's isotope hydrology laboratory and of Eawag's environmental isotope tracer group. The measurement of low-level tritium concentrations will thus be made possible via an improved electrolytic enrichment method for tritium in small volume water samples, followed by low level liquid scintillation counting. The efficient measurement system for natural to ultra low level tritium concentrations, the online monitoring of dissolved gases and the integrated modelling method will provide a new toolbox for the near real-time quantification of the flow and mixing of different groundwater sources in MAR systems. The numerical modelling is based on a high resolution 3-D geological model incorporated into an integrated surface-subsurface hydrological model (ISSHM). The modelling software HydroGeoSphere, the inverse modelling software PEST++ and the data assimilation software PDAF will be used for model construction, model calibration and real time modelling.