Hydrodynamics as multi-scale control on cells and solutes - an overview

The transport of cells and solutes has numerous important applications including movement of pathogens, introduction of organisms for bioremediation of aquifers, and controls on nutrient uptake and carbon processing in stream ecosystems. The transfer of microbial cells and solutes among aquatic habitats is mediated by the movement of water, and the growth of microbial communities reflects local habitat conditions. Conversely the nature of sediment biofilms and other biota can influence the hydraulic conductivity of sediments and the flux of water across the sediment-water interface. At the smallest scales, interaction of water-borne solutes and particles (including cells) with sediment grain surfaces depends on local flow conditions, surface-chemical characteristics such as charge, and removal processes (solute consumption, particle attachment) at the grain surface. At intermediate scales, flow through sediments is a function of the bed structure, which may be modified by micro-and macro-organisms. At the catchment scale, high flow events affect connections among landscape elements, which may be sources of solutes and cells, and perturb processes across a wide variety of scales. Various aquatic communities may be disturbed to different degrees by high flow events, and both the timing and magnitude of these disturbances influence the organization of the physical and biological systems. Feedback between flow, sediment structure, and biological growth ultimately yield diverse habitat conditions, biological communities and metabolic capacity. We propose a framework where large-scale factors such as geomorphology and climate are increasingly modified by biotic influences at smaller scales. Strong coupling across scales and between physical, chemical, and biological processes emphasizes the need to consider system behavior in an integrated fashion