Land use drives large CH₄ fluxes from a highly urbanized Indian estuary

There is growing awareness of the need to better constrain the contribution of atmospheric methane (CH₄) fluxes from urbanized estuaries due to the high global warming potential of CH₄ and the accelerating growth of urban expansion. This study undertook seasonal sampling campaigns to understand the impact of urbanization on atmospheric CH₄ fluxes and their drivers in a large, tropical estuary in India. Overall, the study found that the Cochin estuary emitted large amounts of CH₄ (398.8 ± 141.6 μmolm^-2d^-1) to the atmosphere with CH₄ hotspots reaching up to 939.7 μmolm^-2d^-1 were identified. The strongest drivers of CH₄ dynamics in different anthropogenically impacted zones were traced. The source of organic matter for CH₄ production was revealed to be terrestrial C3 plants, autochthonous production, marine phytoplankton, and sewage inputs. The study suggests that monsoonal urbanized tropical estuaries may be an important but under-recognized element of the global CH₄ budget.