Concentrations, loads and yields of organic carbon from two tropical peat swamp forest streams in Riau province, Sumatra, Indonesia

Tropical peat swamp forest (PSF) stores large quantities of carbon. To estimate how much organic C is released from this type of landscape we determined organic carbon (C) concentrations, loads and yields in two contrasting watercourses draining from PSF in Riau Province, Sumatra (Indonesia). Meranti Ditch (MD) is an artificial watercourse whose small catchment (estimated area 4.8 km2) is in semi-intact condition, whereas Turip River (TR) has a large natural catchment (estimated area 458 km2) covered with fairly intact PSF where > 75% of the original canopy trees remain. The organic C load (Gg C yr-1) of each watercourse was calculated by combining TOC concentration with water discharge rate to give organic C yield (g C m-2 yr-1). Dissolved organic carbon (DOC) was the dominant (95.0-99.8%) component of total organic carbon (TOC) in the water. TOC concentration was 85-94 mg C L-1 in MD and 50-58 mg C L-1 in TR. The high concentration in MD was not surprising because this catchment had been disturbed by repeated phases of logging and a dense network of ditches was excavated ten years ago. The TOC loads were 0.23 Gg C yr-1 in MD and 14.0 Gg C yr-1 in TR. TOC yields (i.e. TOC fluxes through the fluvial system) were 41.6-55.5 g C m-2 yr-1 in MD and 26.2-34.9 g C m-2 yr-1 in TR.