The Impact of Blade Motion on the Flux to a Blade Surface

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Aquatic vegetation in fresh- and salt-water systems provides ecosystem services valued at over one trillion dollars per year. Seagrass and freshwater macrophytes enhance water quality by filtering nutrients from the water, reducing re-suspension, and producing oxygen in stagnant regions. Unlike terrestrial plants, which acquire nutrients through their roots, aquatic plants acquire essential nutrients through their leaves and blades from the surrounding water. The nutrient uptake controls the growth and health of the vegetation, as well as its potential impact on water quality. The proposed research will examine how the hydrodynamic conditions and the motion of individual blades impacts the rate of nutrient flux to the plant, with the goal of providing better predictions of the potential maximum uptake rate. The project will examine the interaction of individual blades with uni-directional current and progressive waves to understand how blade motion influences flux to the blade surface. The model blades will be constructed from low-density polyethylene (LDPE), which preferentially absorb the organic compounds present in our flume water (e.g. chloroform). Because of its high partitioning coefficient, for an initial period of exposure, the LDPE blade takes in chemicals as fast as it can be delivered to the surface, mimicking mass-transport limiting uptake. This project will extend existing models for flux at solid boundaries to conditions relevant to macrophytes, specifically introducing the impact of blade motion and conditions with waves. It will contribute a basic understanding of mass exchange at flexible boundaries that is relevant to chemical and biological engineering.