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

摘要

Sedimentary methane (CH_4) fluxes and oxidation rates were determined over the wet and dry seasons (four measurement campaigns) in Pulicat lake, an extensive shallow estuary in south India. Dissolved CH_4 concentrations were measured at 52 locations in December 2000. The annual mean net CH_4 flux from Pulicat lake sediments was 3.7 x 10~9g yr~(-1) based on static chamber measurements. A further 1.7 x 10~9g yr~(-1) was estimated to be oxidized at the sediment-water interface. The mean dissolved concentration of CH_4 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 x 10~9 g yr~(-1)) of the total CH_4 produced 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 CH_4 from Pulicat lake to be 0.5 to 4.0 x 10~9 g yr~(-1).