Carbon distribution in restored and reference marshes at Blackwater National Wildlife Refuge

Abstract

Tidal marshes are important for the ecosystem of the Chesapeake Bay, east coast USA. They have the capacity to sequester large amounts of carbon as they accrete with sea-level rise. The purpose of this study was to evaluate carbon distributions in a marsh restored using coarse mineral and organic sediments in 2003 and a natural reference marsh. Soil cores were collected across transects in each marsh to a depth of 1 m. Samples were divided by horizon and analyzed for bulk density and carbon concentration. The restored marsh had wider ranges of bulk density and C concentrations due to the presence of both organic and mineral soil materials. Horizons from the restored marsh had a mean bulk density of 0.50 g cm⁻³ while the reference marsh averaged 0.09 g cm⁻³. Carbon concentrations were greater in the reference marsh (30%) than the restored marsh (13%). The average carbon content in the restored marsh was 35 kg m⁻² while the reference marsh has only 24 kg m⁻² due to a greater bulk density. New organic material deposited over the dredge material represents surface carbon accumulation of 1.8 Mg C ha⁻¹ yr⁻¹. Evaluating restoration and carbon dynamics are difficult without knowledge of site characteristics prior to restoration.

Keywords:

• tidal marsh
• wetland restoration
• carbon variability