Estimation of particulate organic carbon export to the ocean from lateral degradations of tropical peatland coasts

Abstract. The amount of particulate organic carbon (POC) export to the ocean due to coastal erosion and peat mass movement events on Bengkalis Island, Indonesia, was estimated. The annual flux of POC to the ocean due to coastal erosion along the research area of Bengkalis Island was estimated to be in the range of 2.06 to 7.60 tC m⁻¹ yr⁻¹. POC exports to the ocean by events of peat mass movement along the coast of the northern part of Bengkalis Island were estimated in a range of 1.43 to 5.41 tC m⁻¹, with an average increase of 2.23 tC m^-1 from 2010 to 2018. The estimation of the POC flux was carried out by combining the analysis of the peat soil and the estimation of the volume of exported peat using aerial photogrammetry and satellite imagery analysis. A linear relationship was found between the area affected by the landslide and the volume of the peat soil divided by area. Coastal erosion and peat mass movements occurred in a chain of events, confirming that peat from coastal areas was exported to the ocean. Annual export of POC from coastal erosion for 1 m was equivalent to annual carbon emissions from degraded peatlands of 0.41 to 1.52 hectares. The carbon export rate per metre from events of peat mass movement corresponds to carbon emissions produced over one year of 0.29 to 1.08 hectares of degraded peatlands. On a peatland coast with an average length of 3,152 metres, the amount of POC exported to the ocean due to events of peat mass movement was estimated to range from 4.45 to 17.1 ktC, while the POC exported due to coastal erosion was estimated to range from 6.35 to 23.9 ktC yr^-1. These lateral carbon exports on the tropical peatland coast indicate a new route of carbon export to the ocean, in addition to the common riverine discharge of organic carbon.