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Abstract:We present annual estimates of the net ecosystem exchange (NEE) of carbon dioxide (CO 2 ) accumulated over one annual cycle

We report the initial results of the methane flux measured using eddy covariance method during summer months from the world's largest mangrove ecosystem, Sundarbans of India. Mangrove ecosystems are known sources for methane (CH 4) having very high global warming potential. In order to quantify the methane flux in mangroves, an eddy covariance flux tower was recently erected in the largest unpolluted and undisturbed mangrove ecosystem in Sundarbans (India). The tower is equipped with eddy covariance flux tower instruments to continuously measure methane fluxes besides the mass and energy fluxes. This paper presents the preliminary results of methane flux variations during summer months (i.e., April and May 2012) in Sundarbans mangrove ecosystem. The mean concentrations of CH 4 emission over the study period was 1682 ± 956 ppb. The measured CH 4 fluxes computed from eddy covariance technique showed that the study area acts as a net source for CH 4 with daily mean flux of 150.22 ± 248.87 mg m −2 day −1. The methane emission as well as its flux showed very high variability diurnally. Though the environmental conditions controlling methane emission is not yet fully understood, an attempt has been made in the present study to analyse the relationships of methane efflux with tidal activity. This present study is part of Indian Space Research Organisation-Geosphere Biosphere Program (ISRO-GBP) initiative under 'National Carbon Project'.

In the present study, we report initial results on analysis of carbon dioxide (CO 2), water vapour (H 2 O), and energy fluxes (sensible and latent heat flux) over teak mixed deciduous forests of Madhya Pradesh, central India, during winter (November 2011 and January 2012) and summer (February-May 2012) seasons using eddy covariance flux tower datasets. During the study period, continuous fast response measurements of CO 2 , H 2 O and heat fluxes above the canopy were carried out at 10 Hz and averaged for 30 minutes. Concurrently, slow response measurements of meteorological parameters are also being carried out. Diurnal and seasonal variations of CO 2 , H 2 O and heat fluxes were analysed and correlated with the meteorological variables. The study showed strong influence of leaf off and on scenario on the CO 2 , H 2 O and energy fluxes due to prevalence of deciduous vegetation type in the study area. Maximum amount of CO 2 was sequestered for photosynthesis during winter (monthly mean of −25 μmol/m 2 /s) compared to summer (monthly mean of −2 μmol/m 2 /s). Energy flux analysis (weekly mean) showed more energy being portioned into latent heat during winter (668 W/m 2) and sensible heat during summer (718 W/m 2).

Coastal ecosystems represent a potential additional source of the greenhouse gas methane (CH 4) that has been insufficiently quantified. Thus, to understand the mechanisms controlling greenhouse gas emissions in these ecosystems, this study investigated CH 4 emissions from and the related microbial properties of mangrove soils. Soil and gas samples were collected from several plots at different distances from the seashore in Soc Trang and Ca Mau in Vietnam, and the Sundarbans in India. Soil samples were incubated under different conditions, i.e., anaerobic or aerobic, and the microbial properties of each soil sample with the addition of different amounts of seawater were analyzed. Relatively high CH 4 fluxes and production were detected during the aerobic incubation of samples from the seashore plots in Soc Trang and Ca Mau. However, CH 4 production was reduced under anaerobic conditions [soil electrical conductivity (EC): 179-289 mS m −1 , pH (H 2 O): 7.45-8.10] compared with aerobic conditions [water content: 38.9-109.2%, EC: 187-299 mS m −1 , pH (H 2 O): 6.86-7.72], but it increased with increasing sulfate concentration, soil EC and cellulase activity and lowering soil pH under anaerobic conditions. Furthermore, mangrove soil with a relatively high level of total organic carbon (C) exhibited relatively high CH 4 production when diluted 4-fold with seawater under anaerobic conditions [water content: 38.9-109.2%, EC: 533 mS m −1 , pH (H 2 O): 6.67]. Nearly all of the DNA bands excised from polymerase chain reaction-denaturing gradient gel electrophoresis contained identical sequences related to archaea from the class Halobacteria. The high potential of the seashore plot for CH 4 emissions could be due to the enhancement of cellulase activity under the intermittent oxygen supply, which promotes polysaccharide depolymerization and subsequently increases anaerobic methanogenic activities during tidal flooding. This study also indicates that the major archaea responsible for CH 4 production require a particular hydrospheric salt concentration and soil pH.

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