Abstract The commonly observed heterogeneous and erratic emissions of methane from lacustrine sediments are difficult to quantify. The combined analysis of methane and noble gas concentrations in the pore water opens a novel route to analyse and quantify such emissions and was used in this work to explore the gas dynamics in the sediments of two lakes with different hydro-geochemical settings. In the hypertrophic Lake Rot the microbial activity in the sediment pore water results in a virtually continuous gas bubble formation and emission. By determining noble gas concentration gradients and the maximum methane supersaturation, the minimum methane emission from the sediment was quantified. The gas evolution in the pore water of the sediments of artificial Lake Lungern is strongly affected by annual lake level variations of up to 20 m. Noble gas concentrations allow past gas dynamics at different lake levels to be traced back. At “hot spots” of bubble emission microbial methane from deeper sediments was released in response to the decreasing hydrostatic pressure, i.e. man-induced lake level drop. Within zones of the sediment that seasonally fall dry, the oxygen supply to the sediment was inferred from the noble gas excess observed in the pore water, which is due to dissolving air bubbles which entered the sediment during the dry period. These case studies demonstrate the potential of the combined analysis of noble gas and CH4 concentrations for exploring the gas dynamics in lacustrine sediments. The feasibility of this method under different conditions calls for an application in other aquatic environments, such as wetlands and oceans.

中文翻译：

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稀有气体作为甲烷过饱和湖相沉积物中气体动力学的示踪剂

摘要 湖相沉积物中常见的不均匀和不稳定的甲烷排放难以量化。孔隙水中甲烷和惰性气体浓度的综合分析开辟了一种分析和量化此类排放的新途径，并在这项工作中用于探索具有不同水文地球化学环境的两个湖泊沉积物中的气体动力学。在肥厚的 Lake Rot 中，沉积物孔隙水中的微生物活动导致几乎连续的气泡形成和排放。通过确定稀有气体浓度梯度和最大甲烷过饱和度，可以量化沉积物中的最小甲烷排放量。人工湖 Lungern 沉积物孔隙水中的气体演化受到高达 20 m 的年湖水位变化的强烈影响。稀有气体浓度可以追溯过去不同湖泊水位的气体动态。在气泡排放的“热点”处，来自更深沉积物的微生物甲烷随着静水压力的降低而释放，即人为引起的湖泊水位下降。在季节性干燥的沉积物区域内，从孔隙水中观察到的稀有气体过量推断沉积物的氧气供应，这是由于在干燥时期进入沉积物的溶解气泡。这些案例研究证明了惰性气体和 CH4 浓度的联合分析在探索湖泊沉积物中的气体动力学方面的潜力。这种方法在不同条件下的可行性需要在其他水生环境中应用，如湿地和海洋。