Xu Tian, Bai Shuang, Sun Jing, Wang Fushun, Ma Shuwen, Ma Jing, Feng Hao, Yang Mengxue, Chen Xue-Ping
School of Environmental and Chemical Engineering, Shanghai University, Shanghai, 200444, China.
School of Environmental and Chemical Engineering, Shanghai University, Shanghai, 200444, China; Department of Ocean Science, The Hong Kong University of Science and Technology, Hong Kong, China.
J Environ Manage. 2025 Sep;391:126587. doi: 10.1016/j.jenvman.2025.126587. Epub 2025 Jul 19.
Methane (CH) dynamics are significantly influenced by thermal stratification in freshwater reservoirs, yet the mechanistic links between stratification-induced redox shifts and sediment-hosted CH cycling remain poorly understood. This study integrates sediment column experiments with molecular analyses to unravel the direct and indirect effects of thermal stratification on CH production and oxidation in Hongfeng Lake, a subtropical reservoir. The results reveal that thermal stratification leads to the formation of unique redox gradients, resulting in two peaks of CH concentration peaks in surface layer (-6 cm) and deeper sediments (19-22 cm), and the fluxes were observed in summer to be 9 times higher than those observed in winter. Isotopic tracing revealed acetate-driven methane increases across the sediment profile, highlighting the impact of algal-derived carbon on promoting methanogenesis. Methane oxidation in surface sediments was promoted by aerobic conditions following the dissipation of thermal stratification. Microbial community analysis showed that methanogenic archaea, particularly Methanocellales and Methanosarciniales, dominated under both conditions, with higher abundances in the presence of labile carbon substrates. The input of organic matter stimulates the decomposition of carbon and the release of methane within the sediment column, posing the risk of a short-term high-concentration methane release. These findings highlight the importance of thermal stratification, algal-derived carbon, and oxygen availability in regulating CH dynamics, providing new insights into the spatial and temporal variability of methane emissions in freshwater reservoirs. It emphasizes the need to quantify the risk of methane release caused by reservoir turbulence in the future and highlights the management through controlling nutrient input and artificially regulating reservoirs.
甲烷（CH）动态受到淡水水库热分层的显著影响，然而分层诱导的氧化还原变化与沉积物中CH循环之间的机制联系仍知之甚少。本研究将沉积物柱实验与分子分析相结合，以揭示热分层对亚热带水库红枫湖CH产生和氧化的直接和间接影响。结果表明，热分层导致独特的氧化还原梯度形成，在表层（-6厘米）和较深沉积物（19 - 22厘米）中产生两个CH浓度峰值，夏季通量比冬季观测到的通量高9倍。同位素示踪显示，整个沉积物剖面中乙酸驱动的甲烷增加，突出了藻类衍生碳对促进甲烷生成的影响。热分层消散后，表层沉积物中的甲烷氧化受到有氧条件的促进。微生物群落分析表明，产甲烷古菌，特别是甲烷杆菌目和甲烷八叠球菌目，在两种条件下均占主导地位，在存在不稳定碳底物时丰度更高。有机物质的输入刺激了沉积物柱内碳的分解和甲烷的释放，带来了短期内高浓度甲烷释放的风险。这些发现突出了热分层、藻类衍生碳和氧气可用性在调节CH动态中的重要性，为淡水水库甲烷排放的时空变异性提供了新的见解。强调了未来量化水库湍流导致甲烷释放风险的必要性，并突出了通过控制养分输入和人工调节水库进行管理的重要性。
