Eddy covariance and CRDS based techniques of GHGs measurements provide additional constraint in partitioning the net ecosystem exchange

Greenhouse gases such as CO₂ and CH₄ are emitted by various sources. Among the natural ecosystems, forests and wetlands are believed to emit sizeable amount of these gases by means of autotrophic, heterotrophic respirations and bacterial activities. Additionally, a relatively new source has been detected; the emission of CH₄ by trees and plants. A growing evidence suggests that a significant amount of CH₄ is generated especially by the trees in forested ecosystems. Eddy-covariance (EC) based technique is widely used to estimate the GHGs and energy fluxes in natural ecosystems. The net ecosystem exchange (NEE), measured by an EC system, typically represents the net CO₂ fluxes arising due to the biosphere's photosynthetic and respirative processes. The net flux derived by this system, is subsequently partitioned into two components, the respired carbon and the assimilated carbon. However, the partitioning processes may have their own shortcomings which introduce significant errors. To reduce the uncertainty, the NEE needs to be constrained by some additional measurement. We have used a real time GHG analyzer in association with an existing EC system in a tropical forest of north-east India, the Kaziranga National Park, to better constrain the above two carbon fluxes. The GHG analyzer provided CO₂ and CH₄ concentrations as well as their carbon isotopic ratios. The isotopic data were used to partition the EC derived NEE records, which showed a good agreement with the EC measurements within the limits of experimental uncertainty. However, long-term observation is required to establish the potential of this relatively new method in this endeavour. Additionally, the isotopic data provided a strong evidence of plant generated CH₄ , which was apparently not possible to identify by the conventional means. This work will present the three years (2016-2018) of NEE data to demonstrate the unique characteristics of the carbon transfer processes of one of the major forested regions of north-east India, with a special reference to its partitioning by means of the isotopic analysis carried out on a campaign mode observation in Feb 2019.