Simultaneous methane mitigation and nitrogen removal by denitrifying anaerobic methane oxidation in lake sediments

Methane (CH₄) is a potent greenhouse gas, with lake ecosystems significantly contributing to its global emissions. Denitrifying anaerobic methane oxidation (DAMO) process, mediated by NC10 bacteria and ANME-2d archaea, links global carbon and nitrogen cycles. However, their potential roles in mitigating methane emissions and removing nitrogen from lake ecosystems remain unclear. This study explored the spatial variations in activities of nitrite- and nitrate-DAMO and their functional microbes in Changdanghu Lake sediments (Jiangsu Province, China). The results showed that although the average abundance of ANME-2d archaea (5.0 × 10⁶ copies g^-1) was significantly higher than that of NC10 bacteria (2.1 × 10⁶ copies g^-1), the average potential rates of nitrite-DAMO (4.59 nmol ¹³CO₂ g^-1 d^-1) and nitrate-DAMO (5.01 nmol ¹³CO₂ g^-1 d^-1) showed no significant difference across all sampling sites. It is estimated that nitrite- and nitrate-DAMO consumed approximately 6.46 and 7.05 mg CH₄ m^-2 d^-1, respectively, which accordingly achieved 15.07-24.95 mg m^-2 d^-1 nitrogen removal from the studied lake sediments. Statistical analyses found that nitrite- and nitrate-DAMO activities were both significantly related to sediment nitrate contents and ANME-2d archaeal abundance. In addition, NC10 bacterial and ANME-2d archaeal community compositions showed significant correlations with sediment organic carbon content and water depth. Overall, this study underscores the dual roles of nitrite- and nitrate-DAMO processes in CH₄ mitigation and nitrogen elimination and their key environmental impact factors (sediment organic carbon and inorganic nitrogen contents, and water depth) in shallow lake, enhancing the understanding of carbon and nitrogen cycles in freshwater aquatic ecosystems.