Greenhouse gas (GHG) emissions from rivers are a critical missing component of current global GHG models. Their exclusion is mainly due to a lack of in-situ measurements and a poor understanding of the spatiotemporal dynamics of GHG production and emissions, which prevents optimal model parametrization. We combined simultaneous observations of porewater concentrations along different beach positions and depths, and surface fluxes of methane and nitrous oxide at a plot scale in a large regulated river during three water stages: rising, falling, and low. Our goal was to gain insights into the interactions between hydrological exchanges and GHG emissions and elucidate possible hypotheses that could guide future research on the mechanisms of GHG production, consumption, and transport in the hyporheic zone (HZ). Results indicate that the site functioned as a net source of methane. Surface fluxes of methane during river water stages at three beach positions (shallow, intermediate and deep) correlated with porewater concentrations of methane. However, fluxes were significantly higher in the intermediate position during the low water stage, suggesting that low residence time increased methane emissions. Vertical profiles of methane peaked at different depths, indicating an influence of the magnitude and direction of the hyporheic mixing during the different river water stages on methane production and consumption. The site acted as either a sink or a source of nitrous oxide depending on the elevation of the water column. Nitrous oxide porewater concentrations peaked at the upper layers of the sediment throughout the different water stages. River hydrological stages significantly influenced porewater concentrations and fluxes of GHG, probably by influencing heterotrophic respiration (production and consumption processes) and transport to and from the HZ. Our results highlight the importance of including dynamic hydrological exchanges when studying and modeling GHG production and consumption in the HZ of large rivers.

中文翻译：

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调节河流的甲烷和一氧化二氮孔隙水浓度和表面通量。

河流中的温室气体（GHG）排放是当前全球温室气体模型的重要缺失组成部分。之所以将其排除在外，主要是由于缺乏原位测量以及对温室气体生产和排放的时空动态缺乏了解，这阻碍了最佳模型参数化。我们结合了在三个调节水位阶段（在上升，下降和下降三个阶段）在一条大型调节河中沿尺度规模同时观察沿不同海滩位置和深度的孔隙水浓度以及甲烷和一氧化二氮的表面通量。我们的目标是深入了解水文交换与温室气体排放之间的相互作用，并阐明可能的假说，这些假说可以指导未来对流变区（HZ）中的温室气体生产，消费和运输机制的研究。结果表明该站点是甲烷的净来源。在三个滩位（浅，中和深）的河水阶段，甲烷的表面通量与甲烷的孔隙水浓度相关。但是，在低水期，中间位置的通量明显更高，这表明低停留时间会增加甲烷排放量。甲烷的垂直剖面在不同深度处达到峰值，表明不同河水阶段的流变混合的幅度和方向对甲烷生产和消耗的影响。根据水柱的高度，该位置充当一氧化二氮的汇或源。在不同的水阶段，一氧化二氮孔隙水浓度在沉积物的上层达到峰值。河流水文阶段可能会通过影响异养呼吸（生产和消费过程）以及往返于高氮区的运输，显着影响孔隙水浓度和温室气体通量。我们的结果强调了在研究和模拟大型河流HZ的温室气体生产和消耗时，包括动态水文交换的重要性。