Manganese (Mn), an element sensitive to redox conditions in aquatic environments, plays a role in numerous biogeochemical cycles. Although the speciation of Mn in lakes largely tracks the availability of dissolved oxygen, direct oxidation of Mn by molecular oxygen occurs slowly and, instead, the majority of Mn oxidation occurs via biotic and abiotic mechanisms involving microbes, organic matter, light, reactive oxygen species, and mineral surfaces. While each of these mechanisms is either known or likely to occur in freshwater, the relative balance and interaction among these biogeochemical pathways in an intact plankton system remains uncertain. We investigated potential abiotic and biotic mechanisms contributing to Mn oxide formation in Lake Erie, which experiences seasonal hypoxia and accumulation of Mn during seasonal stratification. Overall, Mn oxidation rates were much higher in the shallow and highly productive western basin (up to 1.5 μmoles L−1 d−1) compared to the deeper and less productive central basin, where we observed very little Mn oxidation over 7 days. Our experiments suggest that abiotic mechanisms involving mineral surfaces played a larger role than biotic mechanisms, particularly in the light where Mn oxidation was highest. Reactive oxygen species exhibited antagonistic roles: hydrogen peroxide acted as a net reductant for manganese oxides and completely masked oxidation of Mn by the superoxide free radical. These findings show that multiple mechanisms may exert control over the fate of Mn and suggest that Mn released from sediments during hypoxia can potentially remain dissolved in the water for an extended period of time. Since the severity of Lake Erie hypoxia has increased in recent years, and we are becoming increasingly aware of the health effects of Mn in drinking water sources, these findings should help inform efforts to predict when and where Mn will accumulate in the lake water.

中文翻译：

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伊利湖锰 (II) 氧化的生物和非生物机制

锰 (Mn) 是一种对水生环境中氧化还原条件敏感的元素，在众多生物地球化学循环中发挥作用。尽管湖泊中 Mn 的物种形成主要跟踪溶解氧的可用性，但分子氧对 Mn 的直接氧化发生得很慢，相反，大部分 Mn 氧化是通过涉及微生物、有机物、光、活性氧的生物和非生物机制发生的, 和矿物表面。虽然这些机制中的每一种都是已知的或可能发生在淡水中，但在完整的浮游生物系统中，这些生物地球化学途径之间的相对平衡和相互作用仍然不确定。我们研究了导致伊利湖中锰氧化物形成的潜在非生物和生物机制，伊利湖在季节性分层期间经历了季节性缺氧和锰的积累。全面的，与较深且生产力较低的中央盆地相比，浅层和高生产力的西部盆地的锰氧化速率要高得多（高达 1.5 μmoles L-1 d-1），我们在 7 天内观察到很少的 Mn 氧化。我们的实验表明，涉及矿物表面的非生物机制比生物机制发挥了更大的作用，尤其是在 Mn 氧化最高的光照下。活性氧表现出拮抗作用：过氧化氢充当锰氧化物的净还原剂，并完全掩盖了超氧化物自由基对 Mn 的氧化。这些发现表明，多种机制可能会控制 Mn 的命运，并表明缺氧期间从沉积物中释放的 Mn 可能会长时间保持溶解在水中。