Artificial channels, common features of inland waters, have been suggested as significant contributors to methane (CH₄) and carbon dioxide (CO₂) dynamics and emissions; however, the magnitude and drivers of their CH₄ and CO₂ emissions (diffusive and ebullitive) remain unclear. They are characterized by reduced flow compared to the donor river, which results in suspended organic matter (OM) accumulation. We propose that in such systems hydrological controls will be reduced and OM accumulation will control emissions by promoting methane production and outgassing. Here, we monitored summertime CH₄ and CO₂ concentrations and emissions on six newly constructed river-fed artificial channels, from bare riparian mineral soil to lotic channels, under two distinct flow regimes. Chamber-based fluxes were complemented with hydrology, total fluxes (diffusion + ebullition), and suspended OM accumulation assessments. During the first 6 weeks after the flooding, inflowing riverine water dominated the emissions over in-channel contributions. Afterwards, a substantial accumulation of riverine suspended OM (≥50% of the channel’s volume) boosted in-channel methane production and led to widespread ebullition 10× higher than diffusive fluxes, regardless of the flow regime. Our finding suggests ebullition as a dominant pathway in these anthropogenic systems, and thus, their impact on regional methane emissions might have been largely underestimated.

中文翻译：

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有机物质积累和水文学作为新开发的人工渠道中温室气体动力学的驱动因素

人工河道是内陆水域的共同特征，已被认为是甲烷 (CH ₄ ) 和二氧化碳 (CO ₂ ) 动态和排放的重要贡献者；然而，其 CH ₄和 CO ₂排放（扩散和沸腾）的强度和驱动因素仍不清楚。与供体河相比，它们的特点是流量减少，从而导致悬浮有机物 (OM) 积累。我们建议，在此类系统中，水文控制将减少，有机物质积累将通过促进甲烷产生和排气来控制排放。在这里，我们在两种不同的流态下监测了六个新建的河道人工河道（从裸露的河岸矿土到流水河道）的夏季 CH ₄和 CO ₂浓度和排放量。基于室的通量还辅以水文、总通量（扩散+沸腾）和悬浮 OM 积累评估。在洪水发生后的前六周内，流入的河水在排放量中占主导地位，而不是河道内的排放量。此后，河流悬浮 OM（≥河道体积的 50%）的大量积累增加了河道内甲烷的产生，并导致广泛的沸腾，其比扩散通量高 10 倍，无论流态如何。我们的发现表明，沸腾是这些人为系统中的主要途径，因此，它们对区域甲烷排放的影响可能在很大程度上被低估了。