Influence of river discharge on the distribution and flux of methane in the coastal Bay of Bengal

Abstract

Abstract Rivers are known to be strong sources of methane (CH 4 ) to the atmosphere and their discharges may also enhance its flux from the coastal ocean. In order to examine this, CH 4 fluxes to the atmosphere were examined along the coastal Bay of Bengal during peak discharge period. The saturation of CH 4 in the Ganges river was relatively lower (208 ± 7%) than that of Indian peninsular rivers (907 ± 136%). The Ganges discharges into the northwestern (NW) while the peninsular rivers discharge into the central and southwestern (SW) regions of the coastal Bay of Bengal and influence the concentration and saturations of CH 4 in the western coastal Bay of Bengal. Methane was higher (4.4 ± 0.9 nM) and more supersaturated (208 ± 37%) in the SW coastal Bay of Bengal than in the NW region (2.5 ± 0.1 nM and 116 ± 2.6% respectively). The higher concentrations of CH 4 in the SW region were also influenced by mild coastal upwelling. The efflux of CH 4 is estimated as 57.4 ± 19.3 and 14.5 ± 2.3 μmol m − 2 d − 1 from SW and NW regions, respectively, and an average of 38.9 ± 11.3 μmol m − 2 d − 1 . Our study suggests that the western coastal waters of the Bay of Bengal act as strong source of CH 4 to atmosphere. The total flux from Indian coastal waters (estuaries, mangroves and coastal waters) is estimated as 21.9 × 10 9 g CH 4 y − 1 out of which ~ 70% is from the coastal Bay of Bengal and 20% from estuaries.