Seasonal Variations in N‐Containing Bacteriohopanepolyols and Their Aerobic Methane Oxidation Implications in a Tropical Lake

Abstract Tropical lakes are significant sources of atmospheric methane. Understanding and reconstructing methane cycling in these systems is critical for constraining its climatic impact. Certain N‐containing bacteriohopanepolyols (BHPs), potentially associated with methane‐oxidizing bacteria (MOB), show promise as biomarkers for aerobic methane oxidation (AMO), yet their behavior in natural settings is not fully understood. Here, we present seasonal variations of BHPs, particularly MOB‐associated BHPs, from the seasonally stratified tropical Huguangyan maar lake (HGY maar lake) in China over a full year. Various BHPs were detected in this study. Bacteriohopanetetrol‐34S (BHT‐34S), 3‐methyl‐bacteriohopanetetrol (3Me‐BHT), and bacteriohopanepentol (BHpentol) peaked in summer, likely associated with bacterial biomass or increased water temperature. Nucleoside BHPs, including adenosylhopane, adenosylhopane HG‐diMe , and Me‐adenosylhopane HG‐Me , were more abundant in deep waters during several months with no relation with soil input, supporting in situ production. Importantly, alongside established MOB biomarkers such as aminopentol and aminotetrol, ethenolamine‐BHhexol and N‐formylated‐aminopentol also show high potential for tracing MOB. Their abundances were significantly elevated in bottom waters from May to September during stratification, with pronounced peaks during October overturn. Methylcarbamate‐aminoBHPs (MC‐aminoBHPs) showed somewhat distinct patterns, being enriched only in deep waters during stratification but without the pronounced October peak, potentially indicating different MOB communities or environmental conditions favoring their production under low‐oxygen and high‐ammonium conditions. MOB‐associated BHPs exhibited strong seasonal patterns aligning with dissolved methane concentrations and AMO variations in most seasonally stratified lakes. This study reveals, for the first time from a BHP perspective, the seasonal dynamics of AMO in HGY maar lake, including intensified AMO in the hypolimnion during stratification and lake‐wide AMO during October overturn. Our findings support the application of N‐containing BHPs as effective biomarkers for tracing AMO in lakes.