Assessing coastal carbon variability in two Delaware tidal marshes

Coastal wetlands provide numerous ecosystem services, including the ability to sequester and store carbon. Recent initiatives, such as the U.S. Climate Alliance’s National Working Lands Challenge, have sought to better understand and quantify this ‘blue carbon’ storage as a land management approach to maintain, or potentially offset, atmospheric carbon emissions. To build on this effort locally, loss on ignition and elemental analyses were used to assess sediment organic matter, dry bulk density, and carbon density variability within the root zone of a mesohaline and oligohaline tidal marsh in Delaware. Additionally, we assessed sediment carbon variability at depth greater than one meter and quantified the black carbon fraction in the mesohaline tidal marsh. Organic matter concentrations ranged between 11.85 ± 1.19% and 23.12 ± 6.15% and sediment carbon density ranged from 0.03 ± 0.01 g cm−3 to 0.06 ± 0.02 g cm−3 with both found to significantly differ between the mesohaline and oligohaline tidal marsh systems. Significant differences between dominant vegetation types were also found. We used these data to further estimate and valuate the carbon stock at the mesohaline tidal marsh to be 350 ± 310 metric tons of soil carbon accumulation per year with a social carbon value of $40,000 ± $35,000. This work improves our knowledge of Delaware-specific carbon stocks, and it may further facilitate broad estimates of carbon storage in under-sampled areas, and thereby enable better quantification of economic and natural benefits of tidal wetland systems by land managers.