In freshwater lakes, ebullition is an important pathway for biogenic methane (CH4) to escape from sediment and reach the atmosphere. However, the high spatial and temporal variability of ebullition limits our ability to accurately measure or predict CH4 fluxes from lakes. To explore factors controlling the spatial distribution of ebullition, we investigated free gas accumulation in bottom sediment of Lake Kinneret, Israel. Sediment cores were collected from four sites at different water depth and distance from the shore. Sediment porewater was analyzed for dissolved CH4 concentration, pH, DOC, acetate, and sulfate. Anaerobic CH4 production rates in sediment were determined by incubating sediment samples. For characterizing in situ sediment volumetric gas content, hydroacoustic measurements at various frequencies were conducted at the coring sites and along multiple transects across the lake. A minimum in CH4 production was observed in the upper 30 cm of sediment, which coincided with enriched porewater sulfate. The depth-integrated sediment CH4 production provides a robust estimate for long-term ebullition of CH4 from sediment, while short-term variability was associated with seasonal lake level change. Acoustic measurements revealed the absence of free gas in sediments of the littoral zone and low ebullition rates in the shallow water zones. For the first time, this study reports the role of CH4 production in determining the spatial variability of free gas content in freshwater sediments. The results further demonstrate the importance of sediment gas content in explaining spatial variability of gas ebullition in lakes.

中文翻译：

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Kinneret湖沉积气聚集对沸腾空间分布的控制

在淡水湖泊中，沸腾是生物甲烷 (CH4) 从沉积物中逸出并进入大气的重要途径。然而，沸腾的高时空变异性限制了我们准确测量或预测来自湖泊的 CH4 通量的能力。为了探索控制沸腾空间分布的因素，我们调查了以色列 Kinneret 湖底部沉积物中游离气的聚集。从四个不同水深和离岸距离的地点收集沉积物核心。分析沉积物孔隙水的溶解 CH4 浓度、pH、DOC、乙酸盐和硫酸盐。沉积物中的厌氧 CH4 生成速率通过培养沉积物样品来确定。为了表征原位沉积物体积气体含量，在取芯地点和跨湖的多个横断面进行了各种频率的水声测量。在沉积物上部 30 厘米处观察到 CH4 产量最低，这与富集的孔隙水硫酸盐一致。深度整合的沉积物 CH4 产量为沉积物中 CH4 的长期沸腾提供了可靠的估计，而短期变化与季节性湖泊水位变化有关。声学测量表明，沿海地区的沉积物中没有游离气体，浅水区的沸腾率很低。本研究首次报告了 CH4 生产在确定淡水沉积物中游离气体含量的空间变异性方面的作用。