Arsenic speciation was followed monthly along the spring productivity period (January–June 2021) in the Petit Lac (76 m deep) and in April and June 2021 in the Grand Lac (309.7 m deep) of Lake Geneva (Switzerland/France). Lake Geneva is presently an oligo-mesotrophic lake, and As-unpolluted. The water column never becomes anoxic but the oxygen saturation at the bottom of the Grand Lac is now below 30% owing to lack of water column mixing since 2012. Thus, this lake offers excellent conditions to study As behaviour in an unpolluted, oxic freshwater body. The following ‘dissolved’ As species: iAs(III), iAs(III + V), MA(III), MA(III + V), DMA(III + V), and TMAO were analysed by HG-CT-ICP-MS/MS. Water column measurements were complemented with occasional sampling in the main rivers feeding the lake and in the interstitial waters of a sediment core. The presence of MA(III) and TMAO and the predominance of iAs(V) in lake and river samples has been confirmed as well as the key role of algae in the formation of organic species. While the total ‘dissolved’ As concentrations showed nearly vertical profiles in the Petit Lac, As concentrations steadily increase at deeper depths in the Grand Lac due to the lack of mixing and build up in bottom waters. The evaluation of 25 years of monthly data of ‘dissolved’ As concentrations showed no significant temporal trends between 1997 and 2021. The observed seasonal character of the ‘dissolved’ As along this period coincides with a lack of seasonality in As mass inventories, pointing to a seasonal internal cycling of As species in the water column with exchanges between the ‘dissolved’ and ‘particulate’ (i.e., algae) fractions.

中文翻译：

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日内瓦湖（瑞士、法国）中的砷：长期监测，以及未受污染的寡中养湖中的氧化还原和甲基化形态

在 Petit Lac（76 m 深）的春季生产力期（2021 年 1 月至 6 月）以及 2021 年 4 月和 2021 年 6 月在日内瓦湖（瑞士/法国）的 Grand Lac（309.7 m 深）中每月跟踪一次砷形态。日内瓦湖目前是一个寡中养湖，并且没有受到污染。水柱从未缺氧，但由于自 2012 年以来缺乏水柱混合，Grand Lac 底部的氧饱和度现在低于 30%。因此，这个湖提供了研究 As 在未受污染、有氧淡水体中行为的绝佳条件. 以下“溶解”As 物质：iAs( III )、iAs( III + V )、MA( III )、MA( III + V )、DMA( III +V ), 和 TMAO 通过 HG-CT-ICP-MS/MS 进行分析。水柱测量辅之以偶尔在为湖泊供水的主要河流和沉积岩心的间隙水域中进行采样。MA( III ) 和 TMAO的存在以及 iAs( V)的优势) 在湖泊和河流样本中得到证实，以及藻类在有机物种形成中的关键作用。虽然在 Petit Lac 中总“溶解的”As 浓度显示出几乎垂直的分布，但由于缺乏混合并在底部水中积聚，在 Grand Lac 的更深处，As 浓度稳步增加。对“溶解”砷浓度 25 年月度数据的评估显示 1997 年至 2021 年之间没有显着的时间趋势。观察到的“溶解”砷的季节性特征在此期间与大量库存缺乏季节性相吻合，表明水柱中 As 物种的季节性内部循环，在“溶解”和“颗粒”（即藻类）部分之间进行交换。