Reduced Mixing in a Marine Macrophyte Canopy

Abstract

We report the effects of a marine plant canopy on flow in the coastal environment. In addition to reducing the magnitude of the ambient flow, a Zostera marina canopy was observed to undulate under unidirectional flow. Spectral analyses of the velocity fluctuations in the canopy revealed a fundamental frequency of approximately 0.125-0.156 Hz. These fluctuations were not caused by ambient flow conditions but rather by the hydroelasticity of the plants («monami»). Flow within the canopy can be, therefore, considered a function of plant movement rather than ambient conditions. Calculations incorporating these observations and the resistance of the canopy indicate that eddy viscosity is between 10 −5 and 10 −4 m 2 s −1 . Mixing within Z. marina canopies is reduced and more like the deep ocean than the coastal environment (...)