While groundwater and surface waters have been historically treated as separate entities, they represent a continuum in the hydrological cycle. Of particular importance are the water and mass transport processes across aquatic-terrestrial interfaces, including their physical-chemical-biological interactions that take place in a range of different marine and freshwater systems. Such interactions have important implications for water quantity, water quality, and ecological health. Water and mass flows through the interfaces between groundwater and surface waters are crucial as they actively regulate the transfer of nutrients, contaminants, and water between groundwater and surface environments. The importance of the topic is reflected by questions #13 of the 23 unsolved problems in hydrology (UPH): “What are the processes controlling the fluxes of groundwater across boundaries (e.g. groundwater recharge, inter-catchment fluxes and discharge to oceans)?”. Unfortunately, there is still a substantial lack of understanding of the main physical mechanisms ruling water and mass transport along interfaces as well as standardized methods to measure the processes involved along the interfaces. This is because such processes typically integrate a large variety of scientific disciplines such as hydrology, biogeochemistry, biology, physics, and chemistry, and partly because research is often organized by close compartments, lacking a truly holistic and interdisciplinary approach. This session welcomes novel contributions from interdisciplinary research on groundwater–surface water interactions, along a variety of thematic areas, scales, and experimental and modelling-based methodologies and approaches, possibly revealing knowledge gaps and future research needs. Contributions are sought related to the following relevant interfaces:
• groundwater–river Interactions;
• groundwater - vadose zone studies;
• hyporheic zone studies;
• groundwater–lake interactions;
• groundwater–ocean interactions;
• interactions of groundwater with wetlands.