A comparison of CO2 dynamics and air-water fluxes in a river-dominated estuary and a mangrove-dominated marine estuary

The fugacity of CO2 (fCO(2) (water)) and air-water CO2 flux were compared between a river-dominated anthropogenically disturbed open estuary, the Hugli, and a comparatively pristine mangrove-dominated semiclosed marine estuary, the Matla, on the east coast of India. Annual mean salinity of the Hugli Estuary (approximate to 7.1) was much less compared to the Matla Estuary (approximate to 20.0). All the stations of the Hugli Estuary were highly supersaturated with CO2 (annual mean similar to 2200 mu atm), whereas the Matla was marginally oversaturated (annual mean similar to 530 mu atm). During the postmonsoon season, the outer station of the Matla Estuary was under saturated with respect to CO2 and acted as a sink. The annual mean CO2 emission from the Hugli Estuary (32.4 mol Cm-2 yr(-1)) was 14 times higher than the Matla Estuary (2.3 mol Cm-2 yr(-1)). CO2 efflux rate from the Hugli Estuary has increased drastically in the last decade, which is attributed to increased runoff from the river-dominated estuary.