Reservoirs are known to accelerate the mobilization and cycling of mercury and carbon as a result of flooding of terrestrial organic matter, which can lead to environmental concerns at local and broader spatial scales. We explored the covariation of mercury (Hg) and carbon (C) functional pools in natural and recently dammed portions of the aquatic network of the Romaine River watershed in Northern Quebec, Canada, to understand how the fate of these elements varies across systems with contrasting hydrology and environmental conditions. We found that total Hg (THg) concentrations in surface waters were relatively constant along the network, whereas both the concentrations and proportions of MeHg tended to increase in reservoirs compared to surrounding nonflooded systems, and along the cascade of reservoirs. Whereas THg was related to total and terrestrial pools of dissolved organic carbon (DOC), MeHg was weakly related to DOC but strongly linked to surface concentrations of CO₂, as well as to concentrations of iron and manganese. The latter are proxies of cumulative organic matter processing within the network, presumably in anoxic portions of shallow bays, deep reservoir waters, and river sediments, as well as in prior seasons (e.g., under ice). Our results suggest that these deep boreal reservoirs acted more as transformation sites for Hg that was already present than as mobilizers of new Hg, and that under ice metabolism plays a role in MeHg production in these systems as we found strong dichotomies in MeHg patterns between spring and summer.

中文翻译：

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跨过阻塞的北方河道的汞动员和转化与碳加工和水文学有关

众所周知，由于陆生有机物的泛滥，水库会加速汞和碳的动员和循环，这可能导致局部和更广泛的空间尺度上的环境问题。我们探索了加拿大北魁北克省罗曼河分水岭水网中自然和最近受阻的部分中汞（Hg）和碳（C）功能库的协变，以了解这些元素的命运在整个系统中如何变化，而形成对比水文和环境条件。我们发现，沿着网络，地表水中的总Hg（THg）浓度相对恒定，而与周围的非驱替系统以及沿水库级联相比，水库中MeHg的浓度和比例都趋于增加。₂，以及铁和锰的浓度。后者是网络中累积有机物处理的代理，大概是在浅海湾，深水库水和河流沉积物的缺氧部分，以及以前的季节（例如在冰层下）。我们的结果表明，这些深层的北方储集层更多地充当了已经存在的汞的转化场所，而不是新的汞的动员者，并且在冰代谢下，这些系统中的甲基汞生产起了一定的作用，因为我们发现春季之间的甲基汞模式存在强烈的二分法和夏天。