Smelting activities at Giant Mine (Yellowknife, NWT, Canada) have resulted in high sulfate and arsenic concentrations in nearby lakes. Here we tested whether historic smelting affects current mercury (Hg) cycling in 35 freshwater lakes over a 2800 km² area around the former gold mine. We sampled lake water and sediment over three consecutive years (2015–2017) using a factorial sampling design that accounted for different environmental variables known to affect the net methylmercury (MeHg) levels in water. Stable Hg(II) and MeHg isotope tracers were used to quantify Hg methylation and demethylation rate constants in sediments, and 16S rRNA gene amplicon sequencing was used to characterize microbial community structure. This study reveals that the fraction of methylated total Hg (% MeHg) found in surface water is positively correlated to the sulfate gradient, while the rate at which Hg is methylated (K_m) in sediments is negatively correlated with total arsenic, and positively correlated with dissolved organic carbon, total phosphorous, and % MeHg in the water. Furthermore, 6 of the 28 lakes that had detectable demethylation rate constants (K_d) also had significantly lower DOC concentrations than lakes with non-detectable K_d. Our results also show that legacy pollution from smelting activities is affecting the structure of microbial communities in lake sediments. This study reveals the complex dynamics of Hg cycling in this northern environment, highlighting the importance of large-scale studies in which the effect of multiple pollution gradients (e.g. arsenic and sulfate) must be taken into consideration.

中文翻译：

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传统金矿开采对北部淡水湖泊甲基汞循环和微生物群落结构的影响

Giant Mine（Yellowknife，NWT，加拿大）的冶炼活动导致附近湖泊中的硫酸盐和砷浓度很高。在这里，我们测试了历史冶炼是否影响了前金矿周围2800 公里²区域内 35 个淡水湖中当前的汞 (Hg) 循环。我们使用因子采样设计连续三年（2015-2017 年）对湖​​水和沉积物进行采样，该设计考虑了已知影响水中净甲基汞 (MeHg) 水平的不同环境变量。稳定汞( II) 和甲基汞同位素示踪剂用于量化沉积物中汞甲基化和去甲基化速率常数，并使用 16S rRNA 基因扩增子测序来表征微生物群落结构。本研究表明，地表水中甲基化总汞的比例（% MeHg）与硫酸盐梯度正相关，而沉积物中汞甲基化的速率（K _m）与总砷呈负相关，正相关溶解有机碳、总磷和水中的 % MeHg。此外，在具有可检测去甲基化速率常数 ( K _d )的 28 个湖泊中，有 6 个的DOC 浓度也显着低于具有不可检测K _{d 的}湖泊_。我们的研究结果还表明，冶炼活动造成的遗留污染正在影响湖泊沉积物中微生物群落的结构。这项研究揭示了北部环境中汞循环的复杂动态，强调了必须考虑多种污染梯度（例如砷和硫酸盐）影响的大规模研究的重要性。