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Stable Methane Isotopologues From Northern Lakes Suggest That Ebullition Is Dominated by Sub‐Lake Scale Processes
Journal of Geophysical Research: Biogeosciences ( IF 3.7 ) Pub Date : 2020-09-16 , DOI: 10.1029/2019jg005601
Martin Wik 1 , Brett F. Thornton 1 , Ruth K. Varner 2 , Carmody McCalley 3 , Patrick M. Crill 1
Affiliation  

Stable isotopes have emerged as popular study targets when investigating emission of methane (CH4) from lakes. Yet little is known on how isotopic patterns conform to variations in emission magnitudes—a highly relevant question. Here, we present a large multiyear data set on stable isotopes of CH4 ebullition (bubbling) from three small adjacent subarctic lakes. The δ13C‐CH4 and δD‐CH4 range from −78.4‰ to −53.1‰ and from −369.8‰ to −218.8‰, respectively, and vary greatly among the lakes. The signatures suggest dominant hydrogenotrophic methanogenesis, particularly in the deep zones, but there are also signals of seemingly acetoclastic production in some high fluxing shallow areas, possibly fueled by in situ vegetation, but in‐sediment anaerobic CH4 oxidation cannot be ruled out as an alternative cause. The observed patterns, however, are not consistent across the lakes. Neither do they correspond to the spatiotemporal variations in the measured bubble CH4 fluxes. Patterns of acetoclastic and hydrogenotrophic production plus oxidation demonstrate that gains and losses of sediment CH4 are dominated by sub‐lake scale processes. The δD‐CH4 in the bubbles was significantly different depending on measurement month, likely due to evaporation effects. On a larger scale, our isotopic data, combined with those from other lakes, show a significant difference in bubble δD‐CH4 between postglacial and thermokarst lakes, an important result for emission inventories. Although this characteristic theoretically assists in source partitioning studies, most hypothetical future shifts in δD‐CH4 due to high‐latitude lake area or production pathway are too small to lead to atmospheric changes detectable with current technology.

中文翻译:

来自北部湖泊的稳定甲烷同位素同位素表明,次生化作用主要由次湖规模过程控制

在调查湖泊中甲烷(CH 4)的排放时,稳定同位素已成为流行的研究目标。关于同位素模式如何与排放量变化相一致,人们知之甚少,这是一个高度相关的问题。在这里,我们提出了一个大的多年期数据集,这些数据来自三个相邻的小亚北极湖中CH 4沸腾的稳定同位素(冒泡)。的δ 13 C-CH 4和δD-CH 4湖泊之间的范围分别为-78.4‰至-53.1‰和−369.8‰至-218.8‰。这些特征表明,主要是氢营养型甲烷生成,特别是在深部地区,但也有一些信号表明在某些高通量浅水区可能存在原产于植被的燃料,但在某些高通量的浅水区却出现了反碎屑作用,但不能排除沉积物中厌氧CH 4的氧化。替代原因。但是,所观察到的模式在整个湖泊之间并不一致。它们也不对应于所测量的气泡CH 4通量的时空变化。碎屑和氢营养生产加氧化的模式表明,沉积物CH 4的得失主要由湖底规模的过程决定。δD-CH气泡中的4随测量月份的不同而显着不同,这可能是由于蒸发作用所致。在更大的规模,我们的同位素数据,与那些从其它湖泊相结合,显示出一个气泡差异显著δD-CH 4冰后期和热喀斯特湖泊,用于排放清单一个重要的结果之间。虽然这种特性源理论上有助于分区研究,ΔD-CH最假设未来的变化4,由于高纬度湖地区或生产途径太小导致的大气变化以目前的技术检测。
更新日期:2020-10-11
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