# Seasonal Variations of Carbon Dioxide, Water Vapor and Energy Fluxes in Tropical Indian Mangroves
## 5 Conclusions  
This paper presents the first annual assessment of the CO\({}_{2}\) flux of the Sundarbans mangroves ecosystems, India, using the eddy covariance method, and it aids in providing more direct defensible estimates of the carbon sequestration over the Indian sub-continent. The present eddy flux tower is one of the few towers measuring CO\({}_{2}\) fluxes in mangroves across the globe. Eddy covariance-based NEE estimates in the present study area are more reliable in comparison with previously reported estimates due to their continuous measurements throughout the year. The Sundarbans mangroves had proven to be a consistent carbon sink over different months with an annual NEP of 249 \(\pm\) 20 g C m\({}^{-2}\cdot\)year\({}^{-1}\) during April 2012 to March 2013. A seasonal pattern of CO\({}_{2}\) flux has been observed over the study period, indicating higher NEE during October to December 2012 and lower NEE during April to June 2012. Surface energy balance closure, which is a key indicator to the performance of the eddy covariance measurement system [11], is estimated to be 78% in the present study and is in agreement with the reported values [42]. The small bias error estimate obtained after gap-filling the missing NEE values suggests the reliable annual estimates. Our eddy covariance estimates of NEP, GPP and Re were in the range of the globally reported values from different terrestrial ecosystems. PAR was found to be a strong driver for CO\({}_{2}\) sequestration with a maximum quantum efficiency of 0.0398 \(\pm\) 0.0038 (95% confidence) mols CO\({}_{2}\) per mol of absorbed photons in September 2012. It was observed that the partitioning of net radiation into latent and sensible hear flux was uniform throughout the majority of the year, whereas during July to November 2014 the latent heat flux was higher than the sensible heat flux due to the availability of water during the monsoon and post-monsoon months. The total evapotranspiration was estimated to be 715 \(\pm\) 120 mm\(\cdot\)year\({}^{-1}\) over the study period.  
The present study reports a conservative yet reliable NEP estimate of 249 g C m\({}^{-2}\cdot\)year\({}^{-1}\) purely based on half-hourly computed CO\({}_{2}\) fluxes within the fetch of EC instruments and extrapolation of the same over the entire study area with the assumption of uniform homogeneous vegetation. The study does not, however, account for other important elements of aquatic pathways within which factors such as tidal and groundwater CO\({}_{2}\) export and dissolved inorganic and organic carbon (DIC) exports can influence the NEP to a considerable degree ([17; 53]). Information on such holistic factors which drive the carbon fluxes can add value to our current estimates, which the authors envisage in future studies. Long-term research and measurements would help in building continuous and consistent eddy covariance data sets, which will help to understand the ecosystem dynamics (such as seasonal patterns), environment and climate change. Also, the understanding of inter-relationships with bio-physical variables in future studies helps in up-scaling the results the regional scales.  
The present study is funded by Indian Space Research Organisation's--Geosphere Biosphere Program (ISRO--G.B.P). We duly acknowledge [PERSON], Deputy Director, NRSC for his constant support for the study. We also acknowledge the logistic support and necessary permissions extended by [PERSON], [PERSON], D.F.O., and [PERSON], Range Forest Officer, Sundarbans Biosphere Reserve during our field visits to the study site. All authors contributed to the data required for the manuscript. [PERSON] and [PERSON] primarily prepared the manuscript. While [PERSON] and [PERSON] has guided for in correcting, editing and improving the manuscript. The authors declare no conflict of interest.