Tidal marsh restoration on Sapelo Island: A legacy of RJ Reynolds, Jr., Eugene Odum and the University of Georgia Marine Institute

Restoration of tidal marshes throughout the 20th century have attempted to bring back important functions of natural tidal systems. In this study, vertical accretion, organic carbon (C) sequestration, and nitrogen burial were compared between a natural, never diked tidal salt marsh and a hydrologically restored tidal salt marsh on Sapelo Island, Georgia to examine the impacts of restoration years later. 64 years after hydrologic restoration in 1956, the restored marsh studied had higher rates of accretion based on 137Cs and 210Pb (4.8-5.1 mm/yr), C sequestration (118-125 g C/m2/yr) and N burial (8.3-8.8.g N/m2/yr) than the never diked marsh (2.9-3.4 mm/ yr, 75-85 g C/m2/yr, 4.8-5.6 g N/m2/yr). Since maximum 137Cs deposition in 1964, approximately 30 cm of accretion has occurred in the restored marsh while the never diked marsh had approximately 10-30 cm of new soil deposited. The accumulated soil in the restored marsh was comparable to the natural marsh soil in terms of bulk density, percent C and N. However, below this depth, legacy effects from diking could be found through the higher soil bulk density and lower percent organic C and N relative to soils of the natural marsh. Vertical accretion in the natural marsh appears to be keeping pace with the current rate of sea level rise (SLR) (3.4 mm/yr) while accretion in the restored marsh exceeds SLR as the marsh compensates for subsidence that occurred when it was diked. Under current SLR and accretion rates, ecosystem functions of continual sequestration of C and burial of N will be supported. However, as SLR accelerates, the ability of both marshes to sequester C and bury N will depend on their ability to keep pace. If not, the marshes will eventually convert to mudflats or open water with a concurrent loss of these and other ecosystem services.

Automated summary

Restoration of tidal marshes has shown positive effects on vertical accretion, organic carbon sequestration, and nitrogen burial. This study compared a natural tidal salt marsh with a hydrologically restored salt marsh in Sapelo Island, Georgia, and found that the restored marsh had higher rates of accretion, carbon sequestration, and nitrogen burial. The restored marsh has been able to compensate for subsidence caused by dike construction, and current sea level rise and accretion rates support the ecosystem functions. However, the ability of the marshes to sequester carbon and bury nitrogen may be challenged with accelerated sea level rise.