Fluvial organic carbon losses from a Bornean blackwater river

Concentrations of dissolved organic carbon (DOC) and particulate organic carbon (POC) were analysed from the source to the mouth of the River Sebangau in Central Kalimantan, Indonesia during the dry and wet seasons in 2008/2009 and an annual total organic carbon (TOC) flux estimated. DOC concentrations were higher and POC concentrations lower in the wet season compared to the dry season. As seen in other tropical blackwater rivers, DOC concentration is consistently around 10 times greater than POC concentration. We estimate the annual TOC flux discharged to the Java Sea to be 0.46 Tg year−1 comprising of 93% (0.43 Tg) DOC and 7% (0.03 Tg) POC. This equates to a fluvial TOC loss flux per unit area over the entire Sebangau catchment of 88 g C m−2 yr−1. When extrapolating the River Sebangau DOC loss flux (83 g C m−2 yr−1) to the peat covered area of Indonesia (206 950 km2), we estimate a DOC loss of 17.2 Tg C yr−1 or ∼10% of current estimates of the global annual riverine DOC discharge into the ocean.