Turbulence structure and carbon stocks along a seagrass meadow

Jiarui Lei1, Jiao Zhang1 and Heidi Margaret Nepf2, (1)Massachusetts Institute of Technology, Civil and Environmental Engineering, Cambridge, MA, United States, (2)Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, Cambridge, MA, United States
Seagrass meadows help to moderate climate change by sequestering large amounts of carbon, called blue carbon. More than half of the carbon stored in seagrass soils originates outside the meadow, such that carbon storage capacity depends on the tendency for a meadow to capture and retain suspended particles. To accurately assess the global seagrass carbon stocks, it would be useful to understand the spatial heterogeneity of particle retention within individual meadows. In particular, this study examined the variation particle retention from the edge to the interior of a model seagrass meadow. We developed and validated a model to predict the mean and turbulent velocity distribution within a submerged meadow and conducted sediment–deposition experiments to investigate the impact of velocity and turbulence on the retention of fine particles. Under unidirectional currents in the lab flume, we measured the evolution of flow velocity and turbulent kinetic energy (TKE) from the leading edge of a submerged model meadow, which consisted of rigid cylinders or flexible model plants. At the leading edge, high plant-generated turbulence and vertical draft led to low deposition. Farther from the edge, diminished TKE was associated with elevated deposition. In the fully developed region, higher meadow density resulted in lower TKE and more deposition. However, at the leading edge, turbulence and updraft were more significant in denser meadows due to stronger flow diversion.