Abstract
Despite their limited global distribution, mangroves have gained attention as a potential carbon offset option due to their high carbon storage capacity and diverse social and environmental co-benefits. Carbon stock in mangroves (global average=2,790tCO2eq/ha) is about four times higher than in terrestrial forests and contributes to almost 10% (37GtCO2eq) of global terrestrial carbon pool. Mangrove carbon sequestration averages 6.9tCO2eq/ha/yr but may reach more than 20tCO2eq/ha/yr. Literature suggests that over 812,000ha of mangrove areas, spread over 106 countries/territories, show potential for restoration. Furthermore, globally, mangroves have been lost at a rate of 1-2%/yr, which may account for an annual emission of about 0.09-0.45 GtCO2eq/yr that can be potentially avoided through conservation actions.
Mangroves within the Niger Delta Region (NDR) cover 800,000ha (6% of world extent), and contain an estimated carbon stock of 2.2GtCO2eq. In 2017, Eni's subsidiary Nigerian Agip Oil Company (NAOC) launched a voluntary initiative to restore mangroves to promote social and biodiversity benefits while also contributing to offsetting its GHG emissions. A 30-ha pilot restoration area was identified in Okoroma, Bayelsa, where mangroves had failed to naturally recover from oil spills caused by third party interference in 2014. Site assessments were carried out in 2018 and indicated residual soil contamination (hydrocarbons/metals) and low fertility, a typical characteristic of soils in the NDR.
A restoration trial (n=90 seedlings) using nursery-reared seedlings resulted in 100% survivorship and high growth rates, confirming the feasibility of active restoration across the entire site. Although soil contamination was lower than when the spills occurred, we concluded that the combination of residual contamination, low soil fertility and site topography had restricted the natural regeneration process. This in turn risked further soil degradation and ultimately erosion and permanent habitat loss. To prevent this from happening, a long-term restoration program based on the transplantation of fertilized seedlings in partnership with local communities is proposed.
In addition to the benefits to the local communities and the environmental restoration, this project is expected to allow for the sequestration of 2,970tCO2eq in 20 years and avoid the emission of an estimated 60,000tCO2eq from soil carbon, numbers that could be scaled up in the future to a much larger area. The results of this case study further confirm the possibility of using mangroves as a Natural Climate Solution to offset GHG emissions from O&G operations.
Cancer mortality in the Niger Delta Region of Nigeria: A case study of the University of Port Harcourt Teaching Hospital