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Recent interest in the role of sediments in contaminant transport and stream ecology has motivated additional study of both stream-subsurface exchange flows and suspended sediment transport, deposition, and resuspension. Detailed consideration of the hydrodynamic coupling of stream and pore water flows indicates that there will often be a considerable exchange flux between streams and porous stream beds. As a result, suspended sediments are readily carried from the stream into the subsurface where they can deposit due to physico-chemical interactions with the bed sediments. These processes can greatly influence the transport of fine sediments in streams, and also have important implications for the transport and fate of contaminants. Stream-subsurface exchange allows contaminants to interact with streambed sediments, and contaminants such as metals can sorb to colloidal phases, so that contaminant fate also depends to a large extent on the fate of the suspended sediments. Various degrees of interaction between colloids, contaminants, and stream bed sediments can result in a wide range of transport behavior. In addition, contaminant-particle and particle-particle interactions both depend on the background water chemistry (e.g., pH and ionic strength). Fundamental understanding of the underlying processes allows prediction of the coupled transport of suspended sediments and contaminants. These problems have been analyzed by combining fundamental fluid mechanics with appropriate chemical or physico-chemical interactions between contaminants, colloids, and bed sediments. Long-term modeling of fine sediment and contaminant transport in streams will require consideration of dynamic interactions between stream-subsurface exchange hydrodynamics and fine particle transport.
Recent interest in the role of sediments in contaminant transport and stream ecology has motivated additional study of both stream-subsurface exchange buffers and suspended sediment transport, deposition, and resuspension. Detailed consideration of the hydrodynamic coupling of stream and pore water flows that there will often a large exchange exchange flux between streams and porous stream beds. As a result, suspended sediments are readily carried from the stream into the subsurface where they can deposit due to physico-chemical interactions with the bed sediments. These processes can greatly influence the transport of fine sediments in streams, and also have important implications for the transport and fate of contaminants. Stream-subsurface exchange allows contaminants to interact with streambed sediments, and contaminants such as metals can sorb to colloidal phases, so that contaminant fate also depends to a large extent on the fate of the suspended sediments. Various degrees of interaction between colloids, contaminants, and stream bed sediments can result in a wide range of transport behavior. In addition, contaminant-particle and particle-particle interactions both depend on the background water chemistry (eg, pH and ionic strength). Fundamental understanding of the underlying processes allows prediction of the coupled transport of suspended sediments and contaminants. These problems have been analyzed by combining fundamental fluid mechanics with appropriate chemical or physico-chemical interactions between contaminants, colloids, and bed sediments. Long-term modeling of fine sediment and contaminant transport in streams will require consideration of dynamic interactions between stream-subsurface exchange hydrodynamics and fine particle transport.