Long-Term Sediment, Carbon, and Nitrogen Accumulation Rates in Coastal Wetlands Impacted by Sea Level Rise

Abstract

Coastal wetlands provide important ecosystem services, such as carbon and nitrogen sequestration and flood protection, but are vulnerable to increasing sea levels. We examined the vulnerability of coastal wetlands to rising sea levels using radioisotopes (210Pb and 137Cs) to estimate long-term (~100 years) soil accretion rates. We also estimated carbon and nitrogen accumulation rates. We collected soil cores from four transects along the Albemarle-Pamlico Peninsula of North Carolina, an area experiencing high rates of sea level rise. Transects included four wetland types: forested, transitional between forest and marsh, brackish marsh, and estuarine open water. Of the 16 sites we sampled, we were able to estimate accretion rates for 14 using 210Pb and four cores using 137Cs. Only one site had a vertical accretion rate higher than the local rate of sea level rise (0.45 cm year−1): a transitional wetland site with fine sediment sourced from a nearby canal (0.88 cm year−1). Mean vertical accretion across all sites was 0.20 cm year−1. Our results show that most wetlands in the area are vulnerable to future inundation due to current rates of sea level rise. Extrapolating from our measurement to the entire peninsula suggests that if wetlands have room to migrate and transition from forest to marsh, the potential for sea level rise–induced loss of C and N accumulation will be 2–20%, compared to 35–88% when not accounting for wetland transitions, illustrating the importance of allowing space for wetlands to migrate in these changing landscapes.