The effect of unsteady turbulent flows on mass transfer in aquatic environments

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The objectives of the proposed research program are to examine the role of mass transport on fundamental biogeochemical and ecological processes using a combination of experimental, field, and computational approaches. Specifically, I will examine the influence of turbulence on nutrient uptake, suspension feeding/particle fate, and particle flux that occur in the benthos (sediments, macrophytes, bivalves) of aquatic systems. In doing so, I will examine the role of unsteady flow - including the fluid-structure interactions that cause organisms to oscillate - in addition to the influence of mean flow conditions on these processes. My specific objectives are to investigate/determine the: (1) fluid-macrophyte interactions and how turbulence-induced plant movements affect macrophyte productivity through the transport and uptake of dissolved inorganic carbon to the leaf surface where nutrient uptake occurs; (2) fate of particles (including biological ones) transported through beds of suspension feeding freshwater mussels; and (3) the effect of collector motion on particle capture, which is an essential mass transport mechanism. The fulfillment of these objectives relates directly to a better understanding of the productivity and function of aquatic environments.***As an empiricist, I operate within a theoretical framework set by the fluid dynamics and modified by the specific attributes of the organism/system under study. This allows me to establish hypotheses based on existing physical theory and to examine whether ecological/biogeochemical processes conform to the expectations of that theory. In this way, it is possible to draw broader conclusions and further the development of theories of organism-environmental interactions. This often requires the use of a simplification, such as restricting the movement/geometry of an organism and using steady flow conditions, to ensure that conditions conform to the physical model (e.g. leaves of a plant must be flat and parallel to the flow direction to examine mass transport using the flat plate analogy). By incorporating unsteady flow conditions, including flow-induced interactions, I will be able to advance our understanding of biogeochemical/ecological response to hydrodynamics forcing. The results of this research program will facilitate the development of novel models of the unsteady conditions found in nature, which will inform scientists, engineers, and managers. There are direct implications for the fate/transport of contaminants, which are influenced if not dominated by surface phenomena. The results will also be used to address/mitigate the impacts of human activities on habitat and on water quality.**