Lake Willersinnweiher located in south-western Germany is a small eutrophic gravel pit lake fed by sulfate-enriched groundwater. The aim of this study was to investigate the total methane (CH₄) mass balance of Lake Willersinnweiher with a particular focus on the interaction of carbon and sulfur cycling within the lake sediments and the redoxcline of the water column. Our results show that Lake Willersinnweiher permanently releases CH₄ to the atmosphere throughout the whole year 2018 at rates ranging from 5 to 120 mol d⁻¹. Sediment data show the presence of intense anaerobic oxidation of CH₄ in the upper sediment layers during early summer. Here, CH₄ is most likely consumed via sulfate in sulfate–methane transition zones (SMTZs) that have been observed for a few specific freshwater environments only. Seasonal dynamics in biogeochemical processes trigger the non-steady state conditions within the sediments and the CH₄ consumption in the SMTZs. In parallel, CH₄ released from the sediments is completely consumed by aerobic oxidation processes in the redoxcline indicated by minimum CH₄ concentrations with high δ¹³C–CH₄ values. This zone acts as an effective barrier, minimizing CH₄ release into the surface water and the atmosphere and thus CH₄ oversaturation along with near-atmospheric isotopic composition indicate the presence of an additional CH₄ source in the epilimnion of Lake Willersinnweiher.

中文翻译：

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季节性硫酸盐-甲烷过渡带对富含硫酸盐的淡水环境中甲烷循环的影响

位于德国西南部的 Willersinnweiher 湖是一个小型富营养化砾石坑湖，由富含硫酸盐的地下水补给。本研究的目的是调查Willersinnweiher 湖的总甲烷 (CH ₄ ) 质量平衡，特别关注湖泊沉积物中碳和硫循环与水体氧化还原反应的相互作用。我们的结果表明，Willersinnweiher 湖在 2018 年全年以 5 到 120 mol d ^{-1 的}速率向大气永久释放 CH ₄。沉积物数据表明，在初夏，上层沉积物层中存在强烈的 CH ₄厌氧氧化。这里，CH ₄最有可能通过硫酸盐 - 甲烷过渡区（SMTZ）中的硫酸盐消耗，这些过渡区仅在少数特定淡水环境中观察到。生物地球化学过程中的季节性动态触发沉积物中的非稳态条件和SMTZ 中的 CH ₄消耗。同时，从沉积物中释放的CH ₄被氧化还原酶中的有氧氧化过程完全消耗，由具有高 δ ¹³ C–CH ₄值的最低 CH ₄浓度指示。该区域充当有效屏障，最大限度地减少 CH ₄释放到地表水和大气中，从而减少 CH ₄过饱和以及接近大气的同位素组成表明在威勒辛威赫湖的表层中存在额外的 CH ₄源。