The Critical Zone (CZ) encompasses natural and anthropogenic environments where air, water, soil and rock interact with ecosystems and society. Water connects these components through the transfer of matter and energy across a wide range of spatial and temporal scales. Although groundwater is a major reservoir within this integrated system, its role in linking surface and subsurface processes and in shaping the evolution of the CZ remains incompletely understood. The slow and heterogeneous dynamics of groundwater in particular make it challenging to identify how processes operating at different spatial and temporal scales interact and respond to environmental change.

This session welcomes contributions exploring groundwater processes and their interactions with other CZ components, from local to regional scales and from short-term dynamics to long-term evolution. We encourage observational, experimental and modelling studies, as well as approaches combining these perspectives, including data-driven methods and insights from long-term observatories. Contributions may address natural processes, interactions within ecosystems, or anthropogenic influences, including the effects of climate and land use change on groundwater and CZ dynamics.

Topics may include, but are not limited to: groundwater–surface water interactions and hyporheic processes; recharge, evapotranspiration and root-zone dynamics; groundwater-dependent ecosystems; weathering, solute and contaminant transport; mining-impacted and other human-modified systems; cold-region, coastal, karst and crystalline aquifers; and the use of tracers, isotopes and geophysics to constrain CZ processes.

By connecting processes, observations and models, this session aims to foster a more integrated understanding of groundwater within the CZ. We particularly welcome studies that bridge disciplines and scales, and we strongly encourage early-career researchers to submit their work.