Coastal landforms and accumulation of mangrove peat increase carbon sequestration and storage

Study Number

82

Author

Paula Ezcurra, Exequiel Ezcurra, Pedro P. Garcillán, Matthew T. Costa, and Octavio Aburto-Oropeza

Abstract

Given their relatively small area, mangroves and their organic sediments are of disproportionate importance to global carbon sequestration and carbon storage. Peat deposition and preservation allows some mangroves to accrete vertically and keep pace with sea-level rise by growing on their own root remains. In this study we show that mangroves in desert inlets in the coasts of the
Baja California have been accumulating root peat for nearly 2,000 y and harbor a belowground carbon content of 900–34,00 Mg C/ha, with an average value of 1,130 (± 128) Mg C/ha, and a belowground carbon accumulation similar to that found under some of the tallest tropical mangroves in the Mexican Pacific coast. The depth–age curve for the mangrove sediments of Baja California indicates that sea level in the peninsula has been rising at a mean rate of
0.70 mm/y (± 0.07) during the last 17 centuries, a value similar to the rates of sea-level rise estimated for the Caribbean during a comparable period. By accreting on their own accumulated peat, these desert mangroves store large amounts of carbon in their sediments. We estimate that mangroves and halophyte scrubs in Mexico’s arid northwest, with less than 1% of the terrestrial area, store in their belowground sediments around 28% of the total belowground carbon pool of the whole region.

Main Results and Conclusions

• Mangroves are extremely carbon-rich tropical forests, and have an important global role in sequestering and storing carbon.
  • “Duarte and Cebrián (1) showed that mangroves allocate ca. 40% of their net primary productivity (NPP) to excess photosynthetic carbon that is either exported to lagoon and ocean waters or stored underground.” (1)
  • “the soils of mangrove swamps account for the majority (71-98%) of total carbon storage in estuarine systems.” (1)
  • “With only 0.49% of the total area, the mangroves around the Gulf of California store 18% of the total belowground carbon pool of the whole region.” (5)
• Mangroves that accumulate peat over time as a response to water level increases tend to store more carbon than those that only accumulate non-organic muck.
  • “mangroves located in desert and dry-land coasts can store comparable, and often higher, quantities of belowground carbon than their tropical counterparts, contributing disproportionately to the desert carbon pool.” (4)
• Comparing the age of mangroves to the depth of their peat gives an estimate of the historic rate of sea-level change in the area
  • “The presence of large amounts of mangrove peat in the rocky bays of the Gulf of California opens many possibilities for studying in detail the patterns of sea-level rise in the region.” (4)
• Mangroves in deserts and dry-land coasts have the ability to sequester comparable or greater carbon than those in tropical areas. Different coastal environments and topographical features may also affect the ability of mangroves in those areas to store carbon.
• Mangroves and salty scrubs combined store approximately 28% of carbon around the Gulf of California

Works Cited

1. Duarte CM, Cebrián J (1996) The fate of marine autotrophic production. Limnol Oceanogr 41(8):1758-1766.