Methane in Estuarine Discharges to Coastal Ocean – A Study at Ashtamudi Estuary,Kerala,India

Abstract

Wetlands are major natural source of atmospheric methane, a strong greenhouse gas. Methane fluxes from the Ashtamudi Estuary in Kerala, India (Ramsar site no. 1204), to the atmosphere as well as to the coastal ocean were obtained and are reported here. Concentration of methane in water was estimated by extraction and GC analysis. The water exchanges between the estuary and ocean was estimated by LOICZ Modeling Guidelines. Water to air fluxes of methane from the estuary surface was measured by collecting the emissions. Average water to air flux from this estuary with a water cover area of 5500 ha is 0.57 mg/m $^2$ /hr. The estuarine water is super saturated with methane. The average concentration of methane in the estuary is 420 nMol/L. This study indicates that the discharge of methane rich water from estuaries to coastal ocean need be taken into account when methane budgets are prepared.