Tropical Monsoon Climate Influences the Abundance and Vertical Distribution of Methane-oxidizing Bacteria Communities in a Monomictic Lake (Lake Yambo, the Philippines)

Methane-oxidizing bacteria (MOB) reduce the amount of natural methane (CH4) emitted by freshwater lakes to the atmosphere, emphasizing their influence on lake CH4 dynamics and their potential role in mitigating global warming. The study of CH4 dynamics poses interest in the tropical regions as warmer temperatures and climatic factors contribute to higher CH4 production and potential emissions. In this study, the abundance and vertical distribution of three MOB groups (Types I and II, and NC10) in the monomictic Lake Yambo (Laguna, the Philippines) were investigated amid monsoonal changes (stratified and mixed states). MOB were quantified through catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH), and select physicochemical parameters (temperature, dissolved oxygen, pH, chlorophyll, and CH4 concentration) were measured to determine their impact on MOB abundance. During the lake’s contrasting states, the abundance of MOB communities shifted along the water column with significant interaction between depth and season, with NC10 (p = 0.02) indicating abundance variation driven by combined spatiotemporal factors. Type I MOB positively correlated with temperature (r = 0.34; p = 0.05) and pH (r = 0.38; p = 0.03), which suggests their preference for relatively warmer and more basic conditions. This study presents the response of MOB to varying physicochemical characteristics brought upon by monsoonal changes, integrating the implications of tropical lakes, as potent CH4 sinks, on climate change awareness and lake management.