Spatial and temporal distribution of methane in an extensive shallow estuary, south India

Sedimentary methane (CH4) fluxes and oxidation rates were determined over the wet and dry sea-sons (four measurement campaigns) in Pulicat lake, an extensive shallow estuary in south India. Dissolved CH4 concentrations were measured at 52 locations in December 2000. The annual mean net CH4 flux from Pulicat lake sediments was 3.7 × 109 g yr−1 based on static chamber measure-ments. A further 1.7 × 109 g yr−1 was estimated to be oxidized at the sediment–water interface. The mean dissolved concentration of CH4 was 242 nmol l −1 (ranging between 94 and 501 nmol l−1) and the spatial distribution could be explained by tidal dynamics and freshwater input. Sea–air exchange estimates using models, account only for ∼13 % (0.5 × 109 g yr−1) of the total CH4 pro-duced in sediments, whereas ebullition appeared to be the major route for loss to the atmosphere ( ∼ 63 % of the net sediment flux). We estimated the total atmospheric source of CH4 from Pulicat lake to be 0.5 to 4.0 × 109 g yr−1. 1