Carbon Input and Accumulation in Freshwater to Brackish Marshes on the Barrier Islands of Virginia, USA

Barrier island marshes are exceptionally dynamic systems. The objective of this study was to quantify above and belowground net primary production, above and belowground decay, sedimentation rate, and soil carbon pools within four interdunal fresh to brackish marshes on Hog Island, Virginia, USA and to compare carbon input and soil accumulation among marshes with varied susceptibility to overwash. Major carbon fluxes were assessed by the following methods: aboveground net primary production by harvesting biomass throughout the growing season, belowground net primary production with in-growth cores, sedimentation by deposition on sediment plates, and belowground and aboveground decay with litterbags. We expected sites more susceptible to overwash events to have higher carbon inputs and more accumulation in the soil. Sites in the direct overwash path had slower belowground decay rates, and one of these sites also had the slowest aboveground decay rate. The sites most susceptible to overwash had higher ANPP, but did not have higher soil carbon pools. Sites most susceptible to overwash had a higher salinity and bulk density, but did not store more carbon than other sites. As these sites age and the island accretes vertically, it is expected that soil carbon stocks will increase as well.