invited Talk, Hydroeco 2011, Wien: 2011-05-02 - 2011-05-05
The interface between streams and aquifers is an inherently three-dimensional zone that is typically characterized by sharp transitions in hydraulic, thermal and biogeochemical properties. The dynamic processes in this zone facilitate the exchange of water, solutes, and energy (e.g. heat) and have the potential to affect a multitude of environmental processes such as groundwater recharge, environmental flows, the transformation of nutrients, pollutant attenuation, fish spawning and the selection of habitat and refugia. Due to the high temporal dynamics of stream flows and the typical geologic heterogeneity of alluvial aquifers, stream-aquifer exchange is often characterized by complex patterns in space and time. Despite significant improvements in methods and techniques to characterize these patterns and to quantify exchange fluxes our fundamental understanding of the intricate interplay between hydrologic dynamics and biogeochemical processes in this zone and the implications for water quality and nutrient cycling is still weak. Such knowledge, however, is an important prerequisite for a sustainable management of environmental and water resources. Examples of dynamic interactions between streams and their near stream zone will be presented for different stream aquifer systems. The use of physicallybased numerical models to improve our understanding of processes and to facilitate the development of new theories and conceptual models of stream-aquifer interactions is outlined using the example of a simulation study of stream flow generation in a riparian wetland. Combining new enhanced methods to quantify spatial and temporal patterns of river-aquifer exchange with explorative modeling could provide a viable starting point in this context.