Effects of Sediment Composition on Spartina Alterniflora and Juncus Roemerianus Productivity in Coastal Virginia: A Thin-Layer Sediment Placement Experiment

Climate change poses a major threat to the health of estuaries and their coastal wetland systems. The Chesapeake Bay’s coastal salt marshes are at high risk of inundation due to sea-level rise and land subsidence. Restoration techniques for maintaining coastal marsh resistance to sea-level rise are being developed and refined, with thin layer placement (TLP) emerging as a feasible solution in many areas of the United States. Despite TLPs use across the country, additional research is needed on species-specific responses, sediment types, and geographically focused studies in the lower Chesapeake Bay. My research addresses these gaps by combining both greenhouse and in-situ field experimentation to test which sediment composition allows for the greatest vegetation biomass production while still maintaining an increased soil elevation. In the greenhouse, two common marsh plant species, Spartina alterniflora and Juncus roemarianus, were selected. Five centimeters of sediment (locally collected mud, sand, or a 1:1 sand/mud mix) was applied, and subsequent sediment characteristics and vegetation growth were monitored throughout the growing season. The in-situ field experiment focused on just a single species (S. alterniflora) and examined multiple sediment types (mud or a 1:1 sand/mud mix) in the Lynnhaven River Estuary. In the greenhouse, it was found that S. alterniflora and J. roemerianus had different responses to treatment types, with sand negatively affecting Juncus belowground growth and Spartina outperforming Juncus in aboveground growth in the mud treatment. The greenhouse study demonstrated elevation loss across all treatment types with a statistically significant difference between the sand treatment and the mud treatment and control; however, no significant differences between treatments were not seen in the field, potentially indicating that sediment composition of applied material would not be a determining factor in reaching project elevation goals. The results provide a greater understanding of initial marsh plant response in a species-specific manner with the goal of using TLP to enhance salt marsh resilience. With this insight, practitioners can include research findings in future project planning to increase chances of success.