Surface water and ground water have often been approached as separate environments by hydrologists, engineers, and decision makers. The relevance of their interactions for the aquatic ecosystems has consequently been underestimated. In more recent years, the importance of stream-aquifer interactions has been recognized by the scientific community, and the study of the implications of the mixing between surface and subsurface water in the hyporheic zone currently represents an active research field for hydrologists, biologists, and ecologists. It is now clear that the hyporheic exchange influences the transport of nutrients and contaminants within the river corridor, and controls the supply of heat, oxygen, and organic matter to the microorganisms and macroinvertebrates in the streambed sediments. In turn hyporheic exchange is governed by hydrologic controls at different spatial scales (e.g. river channel, alluvial aquifer, regional groundwater flow). Further studies on the links between the hydrological, biochemical, and ecological processes in the hyporeic zone are required in order to clarify the role of the hyporheic zone for the fluvial ecology.

This session solicits both field-based and modelling studies with a focus on:
- The development and application of novel experimental methods to investigate physical and biogeochemical conditions at the groundwater-surface water interface both at rivers and lakes;
- Investigations of the role of hyporheic processes for the retention and natural attenuation of nutrients and pollutants as well as its impacts on surface water and groundwater quality;
- Hydrological, biogeochemical and ecological modelling approaches (e.g. transient storage models, coupled groundwater - surface water models etc.) for applications at different scales;
- The importance of hyporheic controls on surface water and groundwater quality and riparian ecology at different scales;
- Investigations of the implications of groundwater - surface water interactions at their interface for management and risk assessment frameworks in regard to the European Water Framework Directive.