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

Abstract

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 C_org for long periods, although their C_org burial and storage capacity may be affected by on-going sea level rise and human intervention. Geochemical data from published ²¹⁰Pb-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 100years) of C_org 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 δ¹³C to distinguish terrigenous sediments from those accumulated under the influence of marine transgression. Although the accretion rate ranges in all sediment records were comparable, C_org concentrations (0.2-30%), stocks (30-465Mgha^-1, by extrapolation to 1m depth), and burial rates (3-378gm^-2year^-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.

Keywords: Blue carbon; C(org) burial rate; C(org) stock; Sea level rise; Tropical salt marsh.