The mixing zone between groundwater and surface water (hyporheic zone) is a hydraulically dynamic and biogeochemically active interface that is characterised by distinct physical and biogeo-chemical properties (e.g., oxygen concentration, redox potential, temperature fluctations) that are different from both the surface and the subsurface environments.
It has been recognised that the peculiar properties of the hyporheic zone depend on the spatial patters and dynamics of exchange between surface- and groundwater, which are often distinctly different in their chemical and physical characteristics (e.g. redox conditions, nutrients, tem-perature). Complex sequences of redox reactions, which are often mediated by specific species of micro-organisms, result in steep gradients in oxygen and nutrient concentrations with significant ramifications for aquatic ecology and riparian habitat. With its specific capacity for biogeochemical transformations the hyporheic zone can also function as a zone of attenuation for contaminants with implications for water quality at much larger scales (e.g. catchment scale). Due to the complexity of this interface, however, it still remains difficult to describe, quantify and evaluate the hydrological and biogeochemical process dynamics and their interdependencies.
The aim of this session is to improve our understanding of the functioning of the hyporheic zone, with a strong focus on the links between different hydrological, biochemical, and ecological processes. Both theoretical and experimental studies are welcome. In order to facilitate an inter-disciplinary discussion, it is encouraged to stress aspects of the work that would benefit from suggestions by scientists from other fields.

This session specifically solicits papers with a focus on:
- The development and application of novel experimental methods to investigate physical and biogeochemical conditions at the groundwater-surface water interface
- 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 (e.g. transient storage models, coupled groundwater - surface water models etc.).
- 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 in the hyporheic zone for management and risk assessment frameworks in regard to the European Water Framework Directive.