Evidence of methanogenic activity associated with past fish farming in Lake Soyang, South Korea

Abstract

In this study, a 54-cm-long sediment core was collected from an area with a history of fish farming to investigate a potential link between methane production and past aquaculture activities in Lake Soyang, a large artificial lake (ca. 2？110 m water depth, 16.08 km2 in area). Along with bulk elements (carbon and nitrogen), we analyzed specific lipid biomarkers, including n-alkanes, sterols, glycerol dialkyl diethers (DGDs), and glycerol dialkyl glycerol tetraethers (GDGTs). Additionally, we measured the compound-specific carbon isotopic composition (δ13C) of specific lipids, excluding GDGTs. Evidence of prior aquaculture activities was indicated by high total organic carbon content (~ 30 wt%) and elevated concentrations of coprostanol and stigmasterol, reflecting substantial deposition of mixed organic matter (OM) from aquaculture practices, such as fish feed and feces. The δ13C values of sterols (？ 28.4 ± 1.4‰) were relatively enriched compared to those of isoprenoid DGDs, such as archaeol and OH-archaeol (？ 40.0 ± 3.2‰). This suggests that increased acetoclastic methanogenic activities may be closely linked to the assimilation of by-products derived from aquaculture-related OM as potential carbon sources. Our findings highlight the potential importance of methane production within aquaculture systems and the environmental factors influencing this process. These results could inform the development of systematic management strategies to mitigate methane emissions from aquaculture systems.