CO2 partial pressure and CO2 emission in the Lower Mekong River

Abstract

Summary CO2 evasion from freshwaters is recently included in assessing global carbon budgets, while large uncertainty of global estimates results from incomplete spatial coverage of aquatic carbon emission. Here we examined the dissolved inorganic carbon (DIC) and carbon dioxide partial pressure (pCO2) in riverine water from historical records at 46 stations for the period 1972–1998 in the Lower Mekong River (LMR). The river system presented an exceptional temporal and spatial variability of dissolved inorganic carbon (DIC) species. The alkalinity concentration of the LMR varied from 687 to 3189 μeq/l with an average of 1524 μeq/l (median value: 1586 μeq/l), 1.2 times the global median value. Spatial patterns showed diminishing alkalinity downstream at the main-channel stations along the LMR. Similar to many other Himalayan rivers, alkalinity varied seasonally and inversely related to river runoff with a variation factor of 1.2–1.6, despite a water dilution of 7-fold to 13-fold in the summer flood season. The pCO2 levels ranged from 224 to 5970 μatm with a total average of 1090 μatm and obvious monthly and spatial variations. Under-saturated pCO2 samples (