In the past, surface water and ground water have been approached as separate environments by hydrologists, engineers, and decision makers. In consequence, the relevance of interactions between groundwater and surface water for aquatic ecosystems has frequently been underestimated. Recent years have experienced a crucial paradigm shift, progressing from defining rivers and aquifers as discrete, separate entities towards an understanding of groundwater and surface water as integral components of an aquifer-river-continuum with strong mutual influences between river, aquifer and the interconnecting hyporheic zone.

A rapidly increasing number of research projects is investigating the implications of hyporheic exchange on the transport and transformation of nutrients and contaminants within the river corridor, and controls the supply of heat, oxygen, and organic matter to microorganisms and macroinvertebrates in streambed sediments. Research is also focusing on patterns and dynamics of hyporheic exchange in response to hydrologic controls at different spatial and temporal scales (e.g. river channel, alluvial aquifer, regional groundwater flow). Further research is needed for improving the understanding of the links between hydrological, biogeochemical, and ecological process dynamics in hyporheic zones and their implications for fluvial ecology.

We consider up- and downscaling and the development of a general conceptual framework for groundwater-surface water interfaces as most urgent challenges of hyporheic zone research. That is why we welcome especially contributions that aim to close these knowledge gaps and either address scaling issues or the development of a general conceptual framework. Nevertheless, this session also 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.);

- 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.

Invited speakers:
Adam Ward, Watershed Hydrology & Engineering Group at Indiana University
Stanley B. Grant, University of California, Irvine, Director of the UCI Water PIRE