Currently, CO2 emissions from the peat is a global problem. Particularly, it is caused by biodegradation of dry peat or peat fire. In the northern coast of Bengkalis island, peat is flowing out due to coastal erosion, and mangrove tidal flat is formed the west coast by peat. The core samples of the mangrove have been confirmed that the clay layer and the peat layer are in mutual layers, and decomposition was inhabited because these sandwiched peat soils was an anoxic state. In the northern part of the Bengkalis island, peat is sandwiched in the clay layer. Biodegradation can be suppressed by being sandwiched, there is a possibility of suppressing the amount of peat decomposed by providing a place to store peat in tidal flats. In this research, we examined the degree of decomposition of peat accumulated in the mangrove tidal flats and confirmed that decomposition was suppressed for the peat soils in the tidal flat under mangrove trees, we call it “sandwich effect”. The peat materials in deeper layer came from originally peat swamp forest, however, the surface organic materials were thought to be come from mangrove materials. Considering the change from 1988 to 2015, the carbon fixation rate by mangrove is 1.7 × 103 tC km-2 yr-1, the carbon accumulation rate by accumulation of secondary deposition of peat was 7.4×103 tC km-2 yr-1.
Carbon accumulation in the red clay layer of the subsoil in a major river delta: Contribution of secondary carbonate