Rivers are a natural source of methane (CH₄) into the atmosphere and may contribute significantly to total CH₄ emissions. Even though the details of sources of CH₄ in rivers are not fully understood, weirs have been recognized as a hotspot of CH₄ emissions. In this study, we investigated CH₄ production and consumption in air-exposed river sediments along a cross-channel transect located upstream of a weir. stable carbon isotopes were used for determination of individual methanogenic pathways. In order to understand the relationship between physicochemical and biological processes, additional parameters such as organic matter, grain median size, and carbon and nitrogen content were characterized as well. Generally, samples from the surface sediment layer (0-10 cm) had higher CH₄ production than sediments from the deeper layer (10-20 cm) during the incubation experiments. sediments near the bank zones and in the mid-channel were characterized by the highest organic carbon content (6.9 %) as well the highest methanogenic activity (2.5 mmol g–¹ DW d–¹). The CH₄ production was predominated by H₂/CO₂ dependent methanogenesis in the surface sediment layer (0-10 cm), while the proportion of acetoclastic and hydrogenotrophic methanogenesis in the deeper sediment layer (10-20 cm) was balanced. The CH₄ oxidation potential of sediments showed the same spatial pattern as observed for the CH₄ production. Our results showed high spatial variability of sediment CH₄ production and oxidation in the cross-channel profile upstream of the weir, whereas the highest CH₄ dynamics were observed in the littoral zones. This variability was closely linked with the carbon and nitrogen content in the sediment samples.

中文翻译：

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小河流蓄水池跨河道剖面沉积物中甲烷的形成和消耗

河流是进入大气的甲烷 (CH₄) 的天然来源，可能对 CH₄ 的总排放量产生重大影响。尽管尚未完全了解河流中 CH₄ 来源的详细信息，但堰已被认为是 CH₄ 排放的热点。在这项研究中，我们调查了位于堰上游的跨河道横断面暴露于空气的河流沉积物中 CH₄ 的生产和消耗。稳定的碳同位素用于确定各个产甲烷途径。为了了解物理化学和生物过程之间的关系，还表征了其他参数，例如有机质、颗粒中值大小以及碳和氮含量。一般来说，在孵化实验期间，来自表层沉积物层（0-10 厘米）的样品比来自更深层（10-20 厘米）的沉积物具有更高的 CH4 产量。靠近河岸带和中部河道的沉积物的特征是有机碳含量最高 (6.9%) 以及最高的产甲烷活性 (2.5 mmol g–¹ DW d–¹)。CH 4 的产生主要是表层沉积物层（0-10 cm）中依赖于H 2 /CO 2 的产甲烷作用，而深层沉积物层（10-20 cm）中的醋酸碎屑和氢营养产甲烷作用的比例是平衡的。沉积物的 CH 4 氧化电位显示出与 CH 4 生产所观察到的相同的空间模式。我们的结果表明，在堰上游的跨河道剖面中，沉积物 CH₄ 产生和氧化的空间变异性很高，而在沿海地区观察到最高的 CH₄ 动力学。这种可变性与沉积物样品中的碳和氮含量密切相关。