Freshwaters are important emitters of carbon dioxide (CO₂) and methane (CH₄), two potent greenhouse gases (GHGs). While aquatic surface GHG fluxes have been extensively measured, there is much less information about their underlying sources. In lakes and reservoirs, surface GHG can originate from horizontal riverine flow, the hypolimnion, littoral sediments, and water column metabolism. These sources are generally studied separately, leading to a fragmented assessment of their relative role in sustaining CO₂ and CH₄ surface fluxes. In this study, we quantified sources and sinks of CO₂ and CH₄ in the epilimnion along a hydrological continuum in a permanently stratified tropical reservoir (Borneo). Results showed that horizontal inputs are an important source of both CO₂ and CH₄ (>90 % of surface emissions) in the upstream reservoir branches. However, this contribution fades along the hydrological continuum, becoming negligible in the main basin of the reservoir, where CO₂ and CH₄ are uncoupled and driven by different processes. In the main basin, vertical CO₂ inputs and sediment CH₄ inputs contributed to on average 60 % and 23 % respectively to the surface fluxes of the corresponding gas. Water column metabolism exhibited wide amplitude and range for both gases, making it a highly variable component, but with a large potential to influence surface GHG budgets in either direction. Overall our results show that sources sustaining surface CO₂ and CH₄ fluxes vary spatially and between the two gases, with internal metabolism acting as a fluctuating but key modulator. However, this study also highlights challenges and knowledge gaps related to estimating ecosystem-scale CO₂ and CH₄ metabolism, which hinder aquatic GHG flux predictions.

中文翻译：

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改变源和过程，维持沿热带河流到储层系统的表面CO ₂和CH ₄通量

淡水是二氧化碳（CO ₂）和甲烷（CH ₄）的重要排放物，而二氧化碳是两种有力的温室气体（GHG）。虽然已对水面温室气体通量进行了广泛测量，但有关其潜在来源的信息却少得多。在湖泊和水库中，地表GHG可能源于河水的水平流动，次生水，沿海沉积物和水柱的新陈代谢。通常单独研究这些来源，导致对其在维持CO ₂和CH ₄表面通量方面的相对作用进行零碎的评估。在这项研究中，我们量化了CO ₂和CH _4的源和汇在一个永久分层的热带水库（婆罗洲）中沿着水文连续体的后缘。结果表明，水平输入是 上游储层分支中CO ₂和CH ₄（> 90％的地表排放量）的重要来源。但是，这种贡献沿着水文连续性逐渐减弱，在储层主盆地中可以忽略不计，在该主盆地中，CO ₂和CH ₄脱钩并由不同过程驱动。在主盆地，垂直 CO ₂输入和沉积物CH ₄输入分别贡献了60  ％和23  ％分别到达相应气体的表面通量。水柱的新陈代谢对两种气体均显示出宽幅度和范围，使其成为高度可变的组分，但在任一方向上都有很大的潜力影响地面温室气体的收支。总体而言，我们的结果表明，维持表面CO ₂和CH ₄ 通量的源在空间上以及两种气体之间均发生变化，内部代谢起着波动但关键的调节作用。但是，这项研究还强调了与估计生态系统规模的CO ₂和CH ₄代谢有关的挑战和知识差距 ，这阻碍了水生温室气体通量的预测。