Spatial and Seasonal Variation in Surface Water pCO2 in the Ganges, Brahmaputra, and Meghna Rivers on the Indian Subcontinent
2015
Manaka, Takuya | Ushie, Hiroyuki | Araoka, Daisuke | Otani, Souya | Inamura, Akihiko | Suzuki, Atsushi | Zakir Hossain, H. M. | Kawahata, Hodaka
Recent studies have remarked on the importance of direct CO₂ release from river water into the atmosphere on the global carbon cycle over a short timescale. In this study, we investigated carbonate systems, including spatial and seasonal variations of pCO₂, in three major Himalayan rivers in Bangladesh: the Ganges, Brahmaputra, and Meghna Rivers, and their potential importance. Although pCO₂ is known to be low in the upper reaches of these rivers, owing to active chemical weathering, we observed pCO₂ values higher than the atmospheric pCO₂ level along their lower reaches, where deep soils have developed and where high air temperatures promote active soil respiration. By a simple mixing calculation, we found that seasonal variations in these river water carbonate systems are controlled by subsurface water flows. In the rainy season, most of the lowlands are inundated, and the contribution of subsurface flow to river water carbonate systems increases, resulting in higher pCO₂ values. In future research, more detailed spatial and seasonal investigations are required to clarify the role of terrestrial ecosystems, including rivers and the CO₂ flux to the atmosphere, in the global carbon cycle and to examine how that role will change under global warming.
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