Exportation of dissolved (inorganic and organic) and particulate carbon from mangroves and its implication to the carbon budget in the Indian Sundarbans

Abstract

Mangroves are known for exchanging organic and inorganic carbon with estuaries and oceans but studies that have estimated their contribution to the global budget are limited to a fewmangrove ecosystems which exclude world's largest the Sundarbans. Here, we worked in the Indian Sundarbans and in the Hooghly river/estuary in May (pre-monsoon) and December (post-monsoon), 2014. Aims were, i) to quantify the riverine export of particulate organic carbon (POC) and dissolved organic and inorganic carbon (DOC, DIC)) of the Hooghly into the Bay of Bengal (BoB), ii) to estimate the C export (DOC, DIC, POC) from the Sundarbans into the BoB by using a simple mixingmodel, aswell as iii) to revise the existing C budget constructed for themangroves. The riverine exports of POC, DOC and DIC account for 0.07 Tg C yr−1, 0.34 Tg C yr−1 and 4.14 Tg C yr−1, respectively, and were largest during the monsoon period. Results revealed that mangrove plant derived organic matter and its subsequent degradation is the primary source of DIC and DOC in the Hooghly estuary whereas POC is linked to soil erosion. Mangroves are identified as amajor source of carbon (POC, DOC, DIC) transported from the Sundarbans into the BoB, with export rates of 0.58 Tg C yr−1, 3.03 TgC yr−1, and 3.69 Tg C yr−1 respectively, altogether amounting to 7.3 Tg C yr−1. This C export from the Indian Sundarbans exceeds the ‘missing C’ of the previous budget, thus necessitating further research to finally resolve themangrove C budget. However, these first baseline data on C exports fromthe world's largest deltaicmangrove improves limited global data inventory and signifies the need of acquiring more data from different mangrove settings to reduce uncertainties