Limnology Oceanography dataset for Detritus hosted methananogenesis.xlsx

Accumulation of methane in oxic waters of lakes and the ocean has been widely reported. Despite the importance for the greenhouse gas budget, mechanistic controls of such “methane paradox” remain elusive. Here, we use a combination of CH₄concentration and isotopic (δ¹³C_CH4, δD_H2O and δ¹⁸O_H2O) measurements, plankton incubations and microbial community assessments to demonstrate the existence of the methane paradox in oxygenated waters of a meromictic lake (Lake Cadagno, Switzerland). Following mass dynamics using water isotopes, we exclude the possibility that the accumulation of CH₄ at the thermocline results solely from lateral transport. Interannual variability in the magnitude of the methane paradox (between 0.5 and 5 <i>μ</i>mol L⁻¹) is associated to stratification patterns, changes in zooplankton biomass and planktonic detritus accumulation along density gradients, as well as fluctuating microbial cell numbers. The links between hydrodynamic conditions, aggregation of planktonic detritus and its microbiome, as well as the accumulation of CH₄ in the water column are further supported by high-resolution echo-sounder measurements revealing backscatter maxima at the top of the thermocline, where detritus is effectively trapped, and by oxic incubations showing that CH₄ is produced in zooplankton detritus (0.046 nmol L⁻¹ to 0.095 CH₄ mg dry mass L⁻¹ d⁻¹). Our results also show that detritus-hosted methanogenesis is stimulated through the addition of methylphosphonate, suggesting that zooplankton-associated microbiomes exploit organic phosphorus compounds to release CH₄. Understanding the variability of the methane paradox in relation to changing hydrodynamics and plankton communities will be crucial to predict the future role of lakes in the global methane budget.

湖泊与海洋含氧水体中的甲烷累积现象已被广泛报道。尽管该现象对温室气体收支具有重要意义，但这类“甲烷悖论（methane paradox）”的机理调控机制仍不明晰。本研究结合甲烷（CH₄）浓度与同位素（δ¹³C_CH₄、δD_H₂O及δ¹⁸O_H₂O）测定、浮游生物培养实验与微生物群落评估，证实了瑞士卡达诺湖（Lake Cadagno）这一半混合湖（meromictic lake）含氧水体中甲烷悖论的存在。通过水同位素示踪质量动力学过程，本研究排除了温跃层（thermocline）处甲烷累积仅由侧向输运导致的可能性。甲烷悖论强度（0.5至5 μmol·L⁻¹之间）的年际变化，与分层模式、沿密度梯度分布的浮游动物生物量及浮游碎屑累积变化，以及微生物细胞数量的波动均存在关联。水动力条件、浮游碎屑聚集及其相关微生物组与水柱中甲烷累积之间的关联，进一步得到了以下证据的支持：高分辨率回声测深仪测量结果显示，温跃层顶部存在背散射峰值，此处恰好是浮游碎屑被有效截留的区域；有氧培养实验则证实，浮游动物碎屑可产生甲烷，产率范围为0.046 nmol·L⁻¹·d⁻¹至0.095 nmol CH₄·(mg干重)⁻¹·L⁻¹·d⁻¹。本研究结果还显示，添加甲基膦酸酯可促进碎屑宿主产甲烷作用，这表明浮游动物相关微生物组可通过利用有机磷化合物来释放甲烷。阐明甲烷悖论随水动力条件与浮游生物群落变化的变异规律，对预测未来湖泊在全球甲烷收支中的作用至关重要。