Potential for Carbon Sequestration in Transplanted Salt Marshes

Abstract:

The photosynthetic uptake of atmospheric carbon dioxide (CO₂) by tidal salt marshes results in the long-term storage of carbon in the sediment. In recent decades, pressures such as land-use change and sea level rise have significantly reduced the global extent of salt marshes and increased the need for restoration projects. Restored salt marshes have been shown to provide many of the same ecological and economic benefits as natural marshes, including fish habitat, pollution filtration, and shoreline stabilization. Given the high carbon sequestration capacity of tidal marshes, carbon storage is likely an additional benefit of restoration; however, the degree to which restored marshes achieve equivalency with natural marshes in terms of carbon burial has not been well-defined. In this study, annual carbon sequestration rates in transplanted marshes were estimated and belowground carbon stocks were compared in transplanted versus natural marshes. Sediment cores were collected from five transplanted Spartina alterniflora marshes of known age (12-38 years old) in the Newport River Estuary, NC and from two natural marshes of unknown age. Organic matter content was estimated using the loss on ignition method and carbon content was estimated based on previously established relationships. In transplanted marshes, the rate of carbon sequestration in the top 30 cm decreased with marsh age and ranged from 76.70 g C/m²/yr (38 year old marsh) to 212.83 g C/m²/yr (12 year old marsh). The natural marshes contained significantly larger carbon stocks in the top 30 cm (4534.61 – 7790.18 g C m^-2) than the transplanted marshes (1822.97 – 3798.62 g C m^-2). However, the annual sequestration rates in the transplanted marshes are similar to those observed by others in natural marshes, and therefore it is likely that over time restored marshes are capable of accreting belowground carbon stocks equivalent to those found in natural marshes.