Carbon burial and storage in tropical salt marshes under the influence of sea level rise

Coastal vegetated habitats can be important sinks of organic carbon (C-org) and mitigate global warming by sequestering significant quantities of atmospheric CO2 and storing sedimentary Corg for long periods, although their Corg burial and storage capacity may be affected by on-going sea level rise and human intervention. Geochemical data from published Pb-210-dated sediment cores, collected from low-energy microtidal coastal wetlands in El Salvador (Jiquilisco Bay) and in Mexico (Salada Lagoon; Estero de Urias Lagoon; Sian Ka'an Biosphere Reserve) were revisited to assess temporal changes (within the last 100 years) of Corg concentrations, storage and burial rates in tropical salt marshes under the influence of sea level rise and contrasting anthropization degree. Grain size distribution was used to identify hydrodynamic changes, and delta C-13 to distinguish terrigenous sediments from those accumulated under the influence of marine transgression. Although the accretion rate ranges in all sediment records were comparable, Corg concentrations (0.2-30%), stocks (30465 Mg ha(-1), by extrapolation to 1 m depth), and burial rates (3-378 g m(-2) year(-1)) varied widely within and among the study areas. However, in most sites sea level rise decreased C-org concentrations and stocks in sediments, but increased C-org burial rates. Lower C-org concentrations were attributed to the input of reworked marine particles, which contribute with a lower amount of C-org than terrigenous sediments; whereas higher C-org burial rates were driven by higher mass accumulation rates, influenced by increased flooding and human interventions in the surroundings. C-org accumulation and long-term preservation in tropical salt marshes can be as high as in mangrove or temperate salt marsh areas and, besides the reduction of C-org stocks by ongoing sea level rise, the disturbance of the long-term buried C-org inventories might cause high CO2 releases, for which they must be protected as a part of climate change mitigation efforts. (C) 2018 Elsevier B.V. All rights reserved.