Carbon dioxide, water vapour and energy fluxes over a semi-evergreen forest in Assam, Northeast India

Abstract

The eddy covariance method is a powerful technique for quantification of CO 2 , H 2 O and energy fluxes in natural ecosystems. Leaf area index (LAI) and its changes are significant drivers of CO 2 and H 2 O exchange in a forest ecosystem due to their role in photosynthesis. The present study reports the seasonal variation of CO 2 and energy fluxes and their relationship with other meteorological parameters of a semievergreen primary forest of Kaziranga National Park, Assam, India during February 2016-January 2017. The diurnal pattern of half hourly average CO 2 fluxes over the forest was found to be mostly dominated by the incident photosynthetically active radiation. During the period of study, diurnal variations of CO 2 flux showed a maximum value of −9.97 µmol m −2 s −1 in the month of June during summer which is also the beginning of the monsoon season. The monthly averaged diurnal CO 2 flux and variation in LAI of the forest canopy closely followed each other. The annual net ecosystem exchange of the forest estimated from the CO 2 flux data above the canopy is 84.21 g C m −2 yr −1. Further studies are in progress to confirm these findings. The estimated average annual evapotranspiration of the semi-evergreen forest is 2.8 ± 0.19 mm day −1. The study of partitioning of energy fluxes showed the dominance of latent heat fluxes over sensible heat fluxes. The energy balance closure was found to increase with an increase in instability and the highest closure of around 83% was noted under neutral conditions.

The effect of Indian summer monsoon on the seasonal variation of carbon sequestration by a forest ecosystem over North-East India

“…According to our analysis, the forest ecosystem at KNP acted as a net source of CO 2 in 2016 which is supported by the findings of Sarma et al [96]. However, it needs to be cross-checked against multi-year observations so that the interannual variations can be pointed out.…”

“…The flora at KNP comprises of eastern wet alluvial grasslands, Assam alluvial plains semi-evergreen forest, tropical moist mixed deciduous forest, Eastern Dillenia swamp forest and wetlands. More details about the floristic composition can be found in Sarma et al [96]. Major plant species around the canopy include Gmelina arborea Roxb.…”

“…A finer scale information is available in Fig. 6 of Sarma et al [96] that shows the mean monthly diurnal variation of NEE in this ecosystem.…”

Observations and Modeling of GHG Concentrations and Fluxes Over India

“…However, due to spatial variability in GHGs distribution and dynamics, this characteristic feature may differ in specific regions. For example, the eddy covariance-based results show that the deciduous forest (Kaziranga in Assam) in the Northeast India acted as a strong sink of carbon during the pre-monsoon period (May-June; Sarma et al 2018). On the other hand, as mentioned earlier, most of the forests in mainland India sequester significant carbon in the monsoon but maximum carbon during the post-monsoon to early winter.…”

“…The Indian Institute of Tropical Meteorology (IITM), Pune, also established a few flux towers over different ecosystems under the aegis of the MetFlux India project, initiated and funded by the Ministry of Earth Sciences (MoES), Government of India. These sites include a semievergreen moist deciduous forest in Kaziranga National Park over Northeast India (Deb Burman et al 2017Sarma et al 2018), a mangrove forest in Pichavaram (Gnanamoorthy et al 2019) on the southeast coast of India by the Bay of Bengal and an evergreen coniferous forest over the eastern Himalayan range in Darjeeling (Chatterjee et al 2018) in Northeast India. In addition to the GHG fluxes, CO 2 concentration in seawater and atmosphere is also measured in two islands, in Agatti in the Lakshadweep Islands over the Arabian Sea (Kumaresan et al 2018) and Port Blair in the Andaman and Nicobar Islands over the Bay of Bengal as part of the MetFlux India network.…”