Effect of eelgrass Zostera marina canopies on flow and transport

Abstract

Ecological effects of the interaction between submerged aquatic vegetation and currents depend on the plants and their associated organisms as well as the large-scale transport of dissolved and suspended constituents near the canopy. Mathematical models for airflow within plant canopies were adapted to describe water flow through and above meadows of aquatic eelgrass Zostera marina. The resulting model provided the vertical distribution of velocity and shear in a water column within the meadow, and it was developed to automatically conserve flow within the canopy. It was tested and calibrated with data from the laboratory and the field, and it performed adequately. The flow profile was nearly exponential within the canopy and logarithmic above it. The model was used to study how the eelgrass canopy affected the horizontal transport of conservative constituents. The most important finding was that the vertical distribution of a constituent determines whether the canopy will reduce or enhance its transport through the water column. This effect has direct implications for transport of nonconservative constituents such as dissolved oxygen, nutrients, organic carbon, and particulate pollen, larvae, plankton, and detritus. It also has direct implications for biological issues such as vertical distributions of photosynthesis and of recruitment of organisms on blades of grass while they are exposed to varying degrees of currents and shear.