Dynamics and exchange fluxes of methane in the estuarine mangrove environment of the Sundarbans, NE coast of India
M.K. Dutta, C. Chowdhury, T.K. Jana, S.K. Mukhopadhyay
Atmospheric Environment 77 (2013) 631-639
Abstract
The
distribution and exchange fluxes of methane (CH4) were measured in a
mangrove vegetated island and its bordering estuarine system of the Sundarbans
mangrove biosphere from June 2010 to December 2011 on monthly basis. The onset
of methane production is evident in the forest sediment at about 25 cm deep
sediment layer under strong redox condition having an average Eh value of 175.7
mV and showing a 2.8 folds increase in the pore water dissolved methane
concentration at that depth in comparison to the surface layer. The average
diffusive flux of methane from this methane producing layer to surface was calculated
to be 591±106 nmol m -2 d -1. The depth profiles of NO2-
-N, SO4-2-S, acid volatile sulphide, organic carbon
and dissolved methane in the sediment cores from inter-tidal zones showed
distinct trends representing signatures of denitrification, sulfate reduction
and methanogenesis in the sediment layers. The methane emission from the
sedimenteatmosphere interface was observed to be maximum during monsoon and
higher emission rates was recorded from upper littoral zone. The annual average
atmospheric methane mixing ratio was 2.038±0.07 ppmv. This mangrove biosphere
was found to act as source for methane during monsoon while as sink during pre
and postmonsoon seasons. Estuarine surface water showed a very high degree of
super saturation about 2748±730% for dissolved methane at an annual basis and
act as a significant source of methane having an annual average exchange flux
of 408±110 nmol m-2 h-1. A box model approach has been
adopted at annual basis to understand the distribution and dynamics of methane
in this mangrove environment
