The Impact of Seagrass on Sediment Deposition in South Bay, Virginia

The Impact of Seagrass on Sediment Deposition in South Bay, Virginia Charme Kent, Dr. Rip Hale Submerged aquatic vegetation (SAV) provides a variety of ecosystem services including wave attenuation and carbon sequestration. South Bay, Virginia has extensive meadows of eelgrass (Zostera marina) that have developed over the past two decades in response to restoration activities. In this project, we analyze sediment cores collected from vegetated and unvegetated regions of this back-barrier lagoon to understand the impact of seagrass on sediment deposition. We hypothesized that the presence of seagrass will baffle the wave and current energy, resulting in enhanced sediment deposition. In August 2022 we collected two sediment cores in South Bay, which we subsampled at 1-cm increments in the field. Upon returning to the lab, we analyzed the subsamples for their grain size distribution using a laser diffraction method. Preliminary results indicate that the vegetation region experiences finer grained sediment deposition than the unvegetated area. This supports our hypothesis that the vegetated area attenuates wave energy, and that lower energy causes the finer sediments to settle. Interestingly, at both locations we observe that particles in the upper 1-3 cm are finer grained than those deeper in the core. Future research will address whether this is a result of a seasonal change in hydrodynamic conditions, or if instead this is indicative of an overall fining of sediment grain size within the bay, in response to the reemergence of SAV meadows beginning in the early 2000s