Accelerated Sea‐Level Rise Limits Vegetation Capacity to Sequester Soil Carbon in Coastal Wetlands: A Study Case in Southeastern Australia

• Published in: Earth's future Vol. 9; no. 9
• Main Authors: Sandi, S. G., Rodriguez, J. F., Saco, P. M., Saintilan, N., Riccardi, G.
• Format: Journal Article
• Language: English
• Published: Bognor Regis John Wiley & Sons, Inc 01.09.2021; Wiley
• Subjects: Accumulation; Biomass; blue carbon; Carbon; Carbon sequestration; Climate change; Colonization; Conservation; Estuaries; Floods; Geomorphology; Greenhouse effect; Greenhouse gases; Habitats; mangrove; Mangroves; Mineralization; Nature conservation; saltmarsh; Sea level rise; Sediments; Sequestering; Soil dynamics; Soils; Submergence; Tidal flow; Vegetation; wetland modeling; Wetlands; Australia
• ISSN: 2328-4277; 2328-4277
• DOI: 10.1029/2020EF001901

Estimates of global carbon stocks in coastal wetlands reveal that these are some of the most efficient carbon‐sequestering environments in the world, which has prompted a renewed interest in conservation and restoration programs as an opportunity for greenhouse gas abatement. Accumulation of carbon in coastal wetlands is linked to diverse factors such as the type of vegetation, geomorphic setting, and sediment supply. Feedbacks between these factors and the tidal flow conditions drive the dynamics of carbon accumulation rates. Climate change‐induced sea‐level rise has been shown to increase the vulnerability to submergence of saltmarsh and mangroves in coastal wetlands, even if accommodation and landward colonization are possible. These potential losses of wetland vegetation combined with the reduced productivity of newly colonized areas will directly affect the capacity of the wetlands to sequester carbon from sediments and root growth. Here, we implement an eco‐geomorphic model to simulate vegetation dynamics, soil carbon accumulation, and changes in soil carbon stock for a restored mangrove‐saltmarsh wetland experiencing accelerated sea‐level rise. We evaluate model outcomes for existing conditions and two different management scenarios aimed at mitigating sea‐level rise effects and conserve wetland vegetation. Even though some management measures can result in partial conservation of wetland vegetation, they do not necessarily result in the best option for soil carbon capture. Our results suggest that accelerated sea‐level can trigger accelerated wetland colonization resulting in wetland areas with limited opportunities for soil carbon capture from sediment and root mineralization, an issue that has not been considered in previous studies. Plain Language Summary Coastal wetlands are environments with a high capacity to transfer carbon from the atmosphere and accumulate it in the soil. Recently, there has been significant interest in promoting conservation and restoration of wetlands as a means to reduce carbon in the atmosphere. Carbon accumulation depends on the complex interaction between tides, vegetation and sediments. Vegetation produces organic matter and slows down the flows which allow sediments to deposit increasing the surface elevation. Because of rapid sea‐level rise as a result of climate change, coastal wetlands areas are increasingly vulnerable to submergence. Wetland vegetation will colonize new areas inland to compensate for these losses, but this colonization may be limited by human‐made infrastructure. Vegetation losses and limited colonization will result in vegetation with less capacity to accumulate soil carbon. Here, we use a model to study the effects of sea‐level rise on vegetation and soil carbon accumulation. We apply the model to a restored mangrove‐saltmarsh wetland considering different management scenarios during rapid sea‐level rise. Our results suggest that management strategies must integrate the processes described here as management practices can lead to newly colonized vegetation with limited opportunities to accumulate soil carbon. Key Points Wetland losses due to sea‐level rise and reduced productivity of newly colonized areas limit soil carbon sequestration Focus on conservation of wetland vegetation is not necessarily the optimal option for soil carbon sequestration objectives Implementation of eco‐geomorphic frameworks is of major importance for adequately quantifying projections of soil carbon stocks