Dual stable isotope characterization of excess methane in oxic waters of a mesotrophic lake
Dual stable isotope characterization of excess methane in oxic waters of a mesotrophic lake
复制标题
中营养湖含氧水中过量甲烷的双稳定同位素表征
DOI：
10.1002/lno.11566
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发表时间：
2020
影响因子：
4.5
通讯作者：
Maruo Masahiro
中科院分区：
文献类型：
--
作者：
Tsunogai Urumu;Miyoshi Yuko;Matsushita Toshiyuki;Komatsu Daisuke D.;Ito Masanori;Sukigara Chiho;Nakagawa Fumiko;Maruo Masahiro
为了确定淡水环境中常见的含氧地表水柱中过量甲烷的来源，我们测量了日本中营养湖琵琶湖中甲烷的原位浓度和稳定同位素组成（δ13C 和 δ2H）。除了中上层水柱中的值外，还测定了沿岸带和湖底沉积物的值。此外，我们还进行了孵化实验来测量微生物氧化速率和甲烷同位素特征的变化。我们发现在远洋区域测量的甲烷原位浓度和稳定同位素组成存在显着的垂直和季节性变化。我们得出结论，活跃的微生物氧化是远洋水体中甲烷 δ13C 和 δ2H 值变化的主要原因。因此，我们定义了一个新的指标Δ(2,13)来表征溶解甲烷的来源，其中甲烷氧化过程中δ13C和δ2H的变化都得到了纠正。含氧地表水柱中过量的甲烷表现出与沿海地区相似的 Δ(2,13) 值。我们得出的结论是，远洋区域表面的过量甲烷通过横向传输源自沿海区域。沉积物和流入河流附近的缺氧是导致沿海地区水体和远洋地区地表水柱中甲烷富集的原因。
To determine the source of excess methane in oxic, surface‐water columns often found in freshwater environments, we measured the in situ concentration and stable isotopic compositions (δ13C and δ2H) of methane in Lake Biwa, a mesotrophic lake in Japan. The values from the littoral zone and lake‐floor sediments were determined, besides those in the water column of the pelagic zone. Furthermore, we conducted incubation experiments to measure microbial oxidation rates and alterations in the isotopic signatures of methane. We found significant vertical and seasonal variations in both in situ concentrations and stable isotopic compositions of methane measured in the pelagic zone. We concluded that active microbial oxidation was primarily responsible for the variation in δ13C and δ2H values of methane in the pelagic water column. As a result, we defined a new indicator Δ(2,13) to characterize the sources of dissolved methane, in which variations in both δ13C and δ2H during methane oxidation had been corrected. The excess methane in oxic, surface‐water columns exhibited Δ(2,13) values similar to those in the littoral zone. We concluded that excess methane at the surface of the pelagic zone originated from the littoral zone via lateral transport. Anoxic near sediments and inflowing rivers were responsible for methane enrichment in water of the littoral zone and in the surface water columns of the pelagic zone.