Characterizing spatial and seasonal variability of carbon dioxide and water vapour fluxes above a tropical mixed mangrove forest canopy, India

The above canopy carbon dioxide and water vapour fluxes were measured by micrometeorological gradient technique at three distant stations, within the world's largest mangrove ecosystem of Sundarban (Indian part), between April 2011 and March 2012. Quadrat analysis revealed that all the three study sites are characterized by a strong heterogeneity in the mangrove vegetation cover. At day time the forest was a sink for CO₂, but its magnitude varied significantly from -0.39 to -1.33 mg m^-2 s^-1. The station named Jharkhali showed maximum annual fluxes followed by Henry Island and Bonnie Camp. Day time fluxes were higher during March and October, while in August and January the magnitudes were comparatively lower. The seasonal variation followed the same trend in all the sites. The spatial variation of CO₂ flux above the canopy was mainly explained by the canopy density and photosynthetic efficiency of the mangrove species. The CO₂ sink strength of the mangrove cover in different stations varied in the same way with the CO₂ uptake potential of the species diversity in the respective sites. The relationship between the magnitude of day time CO₂ uptake by the canopy and photosynthetic photon flux was defined by a non-linear exponential curve (R² ranging from 0.51 to 0.60). Water vapour fluxes varied between 1.4 and 69.5 mg m^-2 s^-1. There were significant differences in magnitude between day and night time water vapour fluxes, but no spatial variation was observed.