Mangrove vulnerability and potential carbon stock loss from land reclamation in Jakarta Bay, Indonesia

Land reclamation involves extracting fill from some areas (which in the tropics are commonly mangrove and seagrass ecosystems) and transporting and depositing it into zones being reclaimed as land for housing or industrial development. Greenhouse gas (GHG) emissions are produced at various stages of the process (including for instance, from fuel used in dredging equipment). One substantial and site-dependent source of GHG emissions is associated with carbon stock losses resulting from the disturbance and extraction of fill from vegetated marine ecosystems. In this article we focus on these sources of GHG emissions and assess, for the first time, the potential carbon loss from mangrove ecosystems caused by land reclamation activities. To this end, we take a case study of a regionally significant, large-scale reclamation project in Jakarta Bay, Indonesia. The extent of mangroves likely to be impacted by the project was estimated by analysing land satellite (LANDSAT) imagery in the period before and after the start of reclamation activities. The carbon stored in the affected areas was then estimated using field measurements to determine total stocks (biomass and soil organic carbon). Mangroves in the study area at Serang (where sand mining is designated) and Angke (adjacent to deposition site) were estimated to store on average 203.64 Mg C ha(-1), and 531.53 Mg C ha(-1) respectively. The lower carbon stocks at Serang are a consequence of sand mining that occurred there in 2003. The regrown mangroves at Serang are smaller than that at Angke. The near-surface soil organic carbon (SOC) content at Serang was less than at Angke, 17% and 43% of the total respectively. Results also reveal that around 75% of total carbon stocks in both sites are in the form of SOC. We suggest that collating this sort of information about carbon stocks in sites impacted by land reclamation activities can help development planners identify opportunities to reduce GHG emissions. To illustrate, long-term carbon losses due to land reclamation in the case study area could be reduced if dredging is limited to 1 m depth and mangrove areas are actively rehabilitated.