Changing fluxes of carbon and other solutes from the Mekong River

Abstract

Rivers are an important aquatic conduit that connects terrestrial sources of dissolved inorganic carbon (DIC) and other elements with oceanic reservoirs. The Mekong River, one of the worlds largest rivers, is firstly examined to explore inter-annual fluxes of dissolved and particulate constituents during 1923-2011 and their associated natural or anthropogenic controls. Over this period, inter-annual fluxes of dissolved and particulate constituents decrease, while anthropogenic activities have doubled the relative abundance of SO 4 2-', Cl -' and Na +. The estimated fluxes of solutes from the Mekong decrease as follows (Mt/y): TDS (40.4) > HCO 3 -' (23.4) > Ca 2+ (6.4) > SO 4 2-' (3.8) > Cl -' (1.74)∼Na + (1.7) ∼ Si (1.67) > Mg 2+ (1.2) > K + (0.5). The runoff, land cover and lithological composition significantly contribute to dissolved and particulate yields globally. HCO 3 -' and TDS yields are readily predicted by runoff and percent of carbonate, while TSS yield by runoff and population density. The Himalayan Rivers, including the Mekong, are a disproportionally high contributor to global riverine carbon and other solute budgets, and are of course underlined. The estimated global riverine HCO 3 -' flux (Himalayan Rivers included) is 34014 × 10 9 mol/y (0.41 Pg C/y), 3915 Mt/y for solute load, including HCO 3 -', and 13553 Mt/y for TSS. Thereby this study illustrates the importance of riverine solute delivery in global carbon cycling.