Environmental factors influencing methanogenic activity in two contrasting tropical lake sediments

Aim: To investigate the influence of environmental variables on the abundance and activity of methanogenic archaea (MA) in Akkulam-Veli and Vellayani Lake sediments. Methodology: Sediment and overlying water samples (n=5 each) were collected from Veli and Vellayani lakes of Thiruvananthapuram, Kerala. Samples were analysed for environmental variables using standard protocols. Multivariate analysis was done to study the influence of environmental variables on abundance and activity of MA. Results: Environmental variables of overlying water and sediment showed significant variation between the two lakes. Salinity and sulphate were more in Akkulam-Veli than Vellayani, as Akkulam-Veli is a brackish lake and temporarily connected with Arabian Sea. Highly reduced sediments of Akkulam-Veli favoured more population of methylotrophic and acetoclastic MA than Vellayani. A distributional difference of MA with depth was observed in both lakes, which is attributed to availability of more labile organic matter. The methylotrophic MA activity was not significantly different between the two lakes; however, their abundance was significantly different. Nevertheless, methane production was higher in Vellayani than in Akkulam-Veli Lake. PCA revealed that Corg and labile organic matter (LOM) were the important environmental variables influencing methane production potential. Interpretation: Anthropogenic activities like sewage and waste disposal results in increased input of organic matter in lake sediments. The labile organic matter fraction in the sediments favours methanogenic activity thereby resulting in methane production and release from the lakes. Key words: Labile organic matter, Methanogenic archaea, Methane production, Sulphate reduction, Tropical lakes