Abstract. Freshwaters are important emitters of carbon dioxide (CO₂) and methane (CH₄) to the atmosphere, two potent greenhouse gases (GHG). 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 processes 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/sinks of CO₂ and CH₄ in the epilimnion along a hydrological continuum in a permanently stratified tropical reservoir (Borneo Island). Results showed that horizontal inputs are an important source of both CO₂ and CH₄ (18 to 100 % 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 the most influential but uncertain component in the epilimnetic gas budgets. Overall our results show that while sources sustaining surface CO₂ and CH₄ fluxes vary spatially and between the two gases, internal water metabolism remains a dominant driver. 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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在热带水库中维持表面CO ₂和CH ₄通量的来源和过程：水柱代谢的重要性

摘要。淡水是向大气（两种有力温室气体）排放的二氧化碳（CO ₂）和甲烷（CH ₄）的重要排放源。虽然已经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。通常对这些过程进行单独研究，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/汇在一个永久分层的热带水库（婆罗洲岛）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的重要来源（地表排放量的18％至100％）。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输入分别平均占相应气体表面通量的60％和23％。水柱代谢对两种气体均显示出宽幅度和范围，使其成为上层气体预算中最具影响力但不确定的成分。总体而言，我们的结果表明，尽管维持表面CO ₂和CH ₄通量的源在空间上以及两种气体之间都存在差异，但内部水代谢仍是主要驱动因素。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。