Floodplain soils polluted with high levels of mercury (Hg) are potential point sources to downstream ecosystems. Repeated flooding (e.g., redox cycling) and agricultural activities (e.g., organic matter addition) may influence the fate and speciation of Hg in these soil systems. The formation and aggregation of colloids and particles influence both Hg mobility and its bioavailability to microbes that form methylmercury (MeHg). In this study, we conducted a microcosm flooding–draining experiment on Hg-polluted floodplain soils originating from an agriculturally used area situated in the Rhone Valley (Valais, Switzerland). The experiment comprised two 14 d flooding periods separated by one 14 d draining period. The effect of freshly added natural organic matter on Hg dynamics was assessed by adding liquid cow manure (+MNR) to two soils characterized by different Hg (47.3±0.5 or 2.38±0.01 mg kg⁻¹) and organic carbon (OC: 1.92 wt % or 3.45 wt %) contents. During the experiment, the release, colloid formation of Hg in soil solution and net MeHg production in the soil were monitored. Upon manure addition in the highly polluted soil (lower OC), an accelerated release of Hg to the soil solution could be linked to a fast reductive dissolution of Mn oxides. The manure treatments showed a fast sequestration of Hg and a higher percentage of Hg bound by particulate (0.02–10 µm). Also, analyses of soil solutions by asymmetrical flow field-flow fractionation coupled with inductively coupled plasma mass spectrometry (AF4–ICP–MS) revealed a relative increase in colloidal Hg bound to dissolved organic matter (Hg–DOM) and inorganic colloidal Hg (70 %–100 %) upon manure addition. Our experiment shows a net MeHg production the first flooding and draining period and a subsequent decrease in absolute MeHg concentrations after the second flooding period. Manure addition did not change net MeHg production significantly in the incubated soils. The results of this study suggest that manure addition may promote Hg sequestration by Hg complexation on large organic matter components and the formation and aggregation of inorganic HgS_(s) colloids in Hg-polluted Fluvisols with low levels of natural organic matter.

中文翻译：

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受粪肥施用和驱排水循环影响的受污染 Fluviso 中的汞迁移率、胶体形成和甲基化

被高浓度汞 (Hg) 污染的漫滩土壤是下游生态系统的潜在点源。重复洪水（例如氧化还原循环）和农业活动（例如添加有机物质）可能会影响这些土壤系统中汞的归宿和形态。胶体和颗粒的形成和聚集会影响汞的迁移率及其对形成甲基汞 (MeHg) 的微生物的生物利用度。在这项研究中，我们对源自罗纳河谷（瑞士瓦莱州）的一个农业用地的受汞污染的漫滩土壤进行了微观洪水-排水试验。该实验包括两个 14 天的洪水期，由一个 14 天的排水期隔开。通过添加液态牛粪来评估新添加的天然有机物对汞动态的影响（+MNR) 到以不同 Hg（47.3±0.5或2.38±0.01  mg kg ^-1）和有机碳（OC：1.92 wt % 或 3.45 wt %）含量为特征的两种土壤。在实验过程中，监测了土壤溶液中汞的释放、胶体形成和土壤中甲基汞的净产量。在高度污染的土壤（低 OC）中添加粪肥后，Hg 加速释放到土壤溶液中可能与 Mn 氧化物的快速还原溶解有关。粪肥处理显示出快速的 Hg 封存和更高百分比的 Hg 结合颗粒 (0.02–10  µ米）。此外，通过不对称流场-流动分馏结合电感耦合等离子体质谱法 (AF4-ICP-MS) 对土壤溶液的分析表明，与溶解有机物 (Hg-DOM) 结合的胶体 Hg 和无机胶体 Hg (70 %–100 %) 在添加粪肥时。我们的实验表明，在第一个驱油和排水期产生了净甲基汞产量，随后在第二个驱油期后甲基汞绝对浓度下降。添加粪肥不会显着改变培养土壤中的净甲基汞产量。本研究结果表明，添加粪肥可能通过 Hg 络合大有机物组分以及无机 HgS _(s)的形成和聚集来促进 Hg 封存_。 天然有机物含量低的受汞污染的流水溶胶中的胶体。