THE FLUVIAL CARBON CYCLE IN TWO PENINSULAR MALAYSIAN BASINS: AN ISOTOPE RECONNAISSANCE STUDY
The averaged δ13CDIC signatures in river waters are 13C-enriched by about 10‰, relative to the C3 plant source. Given the general absence of carbonates in either watershed, coupled with the observed CO2 overpressures, the probable cause of this enrichment is diffusive fractionation of DIC via CO2 evasion. The average annual efflux of CO2 in the upstream sub-catchment of the Langat and Kelantan rivers (20 x 103 t C/yr and 125 x 103 t C/yr, respectively) is comparable to the fluvial export of dissolved carbon (~18 x 103 t C/yr and 84 x 103 t C/yr, respectively) and particulate organic carbon (~4 x 103 t C/yr and 42 x 103 t C/yr, respectively). However, the combined gas efflux and fluvial export of carbon only amount to less than 2 % of total ecosystem uptake of CO2 within the two basins. The remainder of this carbon is mostly respired back into the atmosphere, although a minor portion may be stored within the watersheds. These findings confirm the more complex role of rivers in the global carbon cycle, beyond that of a simple link between terrestrial and oceanic reservoirs.