Groundwater discharge from the seasonally thawed active layer is increasingly recognized as an important pathway for delivering methane (CH₄) into Arctic lakes and streams, but its contribution to CH₄ emissions from thaw ponds and its influence on the trophic support and nutritional quality of pond food chains remains unexplored. We quantified the transport of CH₄ from the active layer through groundwater discharge into thaw ponds in a subarctic catchment in northern Sweden, using radon (²²²Rn) as groundwater tracer. We analyzed stable isotopes and fatty acids of pond macroinvertebrates to evaluate the potential effects of groundwater‐mediated CH₄ inputs on the aquatic food chains. Our results indicate that active layer groundwater discharge flows are nontrivial (range 6%–46% of pond volume per day) and the associated CH₄ fluxes (median 339 mg C m⁻²day⁻¹, interquartile range [IQR]: 179–419 mg C m⁻² day⁻¹) can sustain the diffusive CH₄ emissions from most of the ponds (155 mg C m⁻² day⁻¹, IQR: 55–234 mg C m⁻² day⁻¹). Consumers in ponds receiving greater CH₄ inputs from the active layer had lower stable carbon (C) isotope signatures that indicates a greater trophic reliance on methane oxidizing bacteria (MOB), and they had lower nutritional quality as indicated by their lower tissue concentrations of polyunsaturated fatty acids. Overall, this work links physical (CH₄ transport from the active layer), biogeochemical (CH₄ emission), and ecological (MOB‐consumer interaction) processes to provide direct evidence for the role of active layer groundwater discharge in CH₄ cycling of subarctic thaw ponds.

中文翻译：

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活性层中甲烷的运输在维持北极池塘甲烷排放和食物链中的作用

从季节性融化的活动层中排出的地下水日益被认为是将甲烷（CH ₄）输送到北极湖泊和溪流中的重要途径，但是它对融化池中CH ₄排放的贡献及其对池塘营养支持和营养品质的影响食物链尚待探索。我们使用ra（²²² Rn）作为地下水示踪剂，对从活动层通过地下水排泄到瑞典北部亚弧集水区的解冻池中的CH ₄的迁移进行了量化。我们分析了池塘大型无脊椎动物的稳定同位素和脂肪酸，以评估地下水介导的CH ₄的潜在影响水生食物链上的投入。我们的结果表明，活动层地下水的排放量是微不足道的（每天池塘流量的6％–46％）和相关的CH ₄通量（339 mg C m ^-2天^-1的中位数，四分位数范围[IQR]：179– 419 mg C m ^-2 天^-1）可以维持大部分池塘的CH ₄扩散排放（155 mg C m ^-2天^-1，IQR：55-234 mg C m ^-2 天^-1）。池塘中的消费者获得更高的CH ₄来自活性层的输入具有较低的稳定碳（C）同位素特征，表明对甲烷氧化细菌（MOB）的营养依赖性更高，并且由于其较低的组织多不饱和脂肪酸浓度而具有较低的营养品质。总的来说，这项工作将物理过程（从活动层传输CH ₄），生物地球化学过程（CH ₄排放）和生态过程（MOB与消费者的相互作用）联系在一起，从而为活动层地下水排放在亚弧CH ₄循环中的作用提供直接证据解冻的池塘。