Mangroves are one of the most efficient organic carbon sink ecosystems which occur along intertidal coastal areas of tropical and subtropical regions. Together with other coastal wetlands such as saltmarsh and seagrass, mangroves have been termed ‘blue carbon’ ecosystems due to their substantial capacity for carbon storage and sequestration. Consequently, policymakers and stakeholders promote mangroves for natural-based climate change mitigation. However, many mangroves across the world are being altered by anthropogenic disturbances including land-use and land-cover change (LULCC). Large-scale LULCC will inevitably affect the magnitude and direction (loss or gain) of the carbon cycle in mangroves.
The overarching goal in this study was to assess the dynamics of mangrove carbon stocks for the Papua region of Indonesia. This region supports globally significant mangrove estate due to its large extent (~10% of world’s mangrove area), its conservation status, and its potential carbon storage but with evidence of increasing land-use change. To achieve this goal, this study consisted of: 1) a systematic review and meta-analysis to synthesis current evidence quantifying the effect of LULCC on mangrove blue carbon stocks at global scale; 2) field data collection across a widely distributed site network representative of different numbers of hydro-geomorphic settings and LULCCs to assess carbon stocks as well as their rates of loss and gain over space and time; 3) assess rates of carbon burial and identify their sources.
The systematic review and meta-analysis revealed few studies (n=37 publications) that comprised paired LULCC-affected (treatment) and undisturbed mangrove (control) sites. Relative loss and gain of carbon stocks following LULCC were varied depending on the types of LULCC, time since LULCC, and geographical and climatic conditions. From field assessment, carbon stocks in undisturbed mangroves were highly variable, ranged from 182 – 2730 (mean ± SD: 1087 ± 584) Mg C ha–1, which was dependent on hydro-geomorphic settings as well as organic soil depth (211 ± 79 cm). Mangrove conversion to aquaculture resulted in a major loss of soil carbon (60%) and biomass (77%). In contrast, timber harvesting resulted in 75% of a direct biomass loss with no impact on soil carbon stocks. Mangrove regeneration following timber harvesting took 25 years to recover the lost biomass with annual biomass accumulation rates of 1.7 – 4.8 (mean ± SD: 3.7 ± 3.0) Mg C ha–1 yr–1. In undisturbed mangrove, the background soil carbon burial rates ranged from 0.21 – 1.19 Mg C ha–1 yr–1, with observed variation dependant on the hydro-geomorphic setting. The highest rates of burial were associated with high tidal elevation where the autochthonous source was dominant. For low tidal elevation sites, carbon burial rates were low and tended to be external in origin (allochthonous).
In summary, Papuan mangrove holds a substantial asset for national and global blue carbon management, and therefore climate change mitigation policy. In addition, the potential carbon sequestration and other co-benefits that these mangrove ecosystems provide would be lost if high intensity land-use change were to occur across these estates. Findings from this thesis will be essential to guide policymakers and will inform climate change mitigation strategies at both regional and national scales.
|Date of Award||27 Aug 2020|
|Supervisor||Lindsay B. Hutley (Supervisor)|