Influence of seasons and environmental variables on methane dynamics in the Muthukuda Mangrove sediments of Tamil Nadu

Aim: In order to understand the methane biochemistry in the Muthukuda mangrove ecosystem, this study aimed to report on methane production, oxidation, flux, and also to investigate the effect of seasons and environmental variables on methane dynamics. Methodology: Sediment analysis was carried out monthly for a year (2021-2022) from the Muthukuda mangrove, south-east coast of India, which is an unexplored region in terms of methane dynamics. Methane parameters methane concentration, methane oxidation, methane production and methanotrophic enumeration were analysed from the sediment samples collected by a PVC corer from the study site. The methane parameters were analysed using standard methods by gas chromatography. The physiological parameters were analysed on the site using portable probes. Results: The physio-chemical parameters varied with the changing seasons at different depths. The concentrations of organic parameters were higher for carbohydrates, followed by lipids and proteins. LOM was higher in the surface and mid sediments in all the seasons. The concentration of methane was higher during summer in surface sediments. Generally, higher methane oxidation was observed in the mid and bottom sediments during all the seasons. Methanotrophic enumeration ranged from 0.4 ±0.7 to 4.8±2.4 x108 g-1. Interpretation: The results suggest that the bacterial community was involved in both methane oxidation and production, though oxidation of methane was lesser than production contributing to the atmospheric methane, methanotrophic bacteria which oxidizes methane significantly playing a major role in the regulation of methane flux. Key words: Methane oxidation, Methanotrophs, Muthukuda mangrove