Low CO2 evasion rate from the mangrove-surrounding waters of the Sundarbans
Anirban Akhand, Abhra Chanda, Kenta Watanabe, Sourav Das, Tatsuki Tokoro, Kunal Chakraborty, Sugata Hazra, Tomohiro Kuwae
Abstract
Abstract Globally, water bodies adjacent to mangroves are considered significant sources of atmospheric CO 2 . We directly measured the partial pressure of CO 2 in water [ p CO 2 (water)] and related biogeochemical parameters with high temporal resolution, covering both diel and tidal cycles, in the mangrove-surrounding waters around the northern Bay of Bengal during the post-monsoon season. Mean p CO 2 (water) was marginally oversaturated in two creeks (470 ± 162 µatm, mean ± SD) and undersaturated in the adjoining estuarine stations (387 ± 58 µatm) compared to atmospheric p CO 2 , and was considerably lower than the global average. We further estimated the p CO 2 (water) and buffering capacity of all possible sources of the mangrove-surrounding waters and concluded that their character as a CO 2 sink or weak source is due to the predominance of marine water from the Bay of Bengal with low p CO 2 and high buffering capacity. Marine water with high buffering capacity suppresses the effect of p CO 2 increase within the mangrove system and lowers the CO 2 evasion even in creek stations. The δ 13 C of dissolved inorganic carbon (DIC) in the mangrove-surrounding waters indicated that the DIC sources were a mixture of mangrove plants, pore-water, and groundwater, in addition to marine water. Finally, we showed that the CO 2 evasion rate from the estuaries of the Sundarbans is much lower than the recently estimated world average. Our results demonstrate that mangrove areas having such low emissions should be considered when up-scaling the global mangrove carbon budget from regional observations.