A 1-D biogeochemical reactive transport model with a full set of equilibrium and kinetic biogeochemical reactions was developed to simulate the fate and transport of arsenic and mercury in subaqueous sediment caps. Model simulations (50 years) were performed for freshwater and estuarine scenarios with an anaerobic porewater and either a diffusion-only or a diffusion plus 0.1-m/year upward advective flux through the cap. A biological habitat layer in the top 0.15 m of the cap was simulated with the addition of organic carbon. For arsenic, the generation of sulfate-reducing conditions limits the formation of iron oxide phases available for adsorption. As a result, subaqueous sediment caps may be relatively ineffective for mitigating contaminant arsenic migration when influent concentrations are high and sorption capacity is insufficient. For mercury, sulfate reduction promotes the precipitation of metacinnabar (HgS) below the habitat layer, and associated fluxes across the sediment–water interface are low. As such, cap thickness is a key design parameter that can be adjusted to control the depth below the sediment–water interface at which mercury sulfide precipitates. The highest dissolved methylmercury concentrations occur in the habitat layer in estuarine environments under conditions of advecting porewater, but the highest sediment concentrations are predicted to occur in freshwater environments due to sorption on sediment organic matter. Site-specific reactive transport simulations are a powerful tool for identifying the major controls on sediment- and porewater-contaminant arsenic and mercury concentrations that result from coupling between physical conditions and biologically mediated chemical reactions.

中文翻译：

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水下沉积物盖的反应性运输模型及其对砷，汞和甲基汞的长期命运的影响。

建立了具有一整套平衡和动力学生物地球化学反应的一维生物地球化学反应性输运模型，以模拟砷和汞在水下沉积物盖中的命运和输运。对带有厌氧孔隙水的纯水和河口情景进行了模型模拟（50年），或者仅通过扩散，或者通过扩散加上通过顶盖的每年0.1m / m的对流通量。在添加有机碳的情况下，模拟了帽顶0.15 m顶部的生物栖息地层。对于砷而言，硫酸盐还原条件的产生限制了可用于吸附的氧化铁相的形成。结果，当进水浓度高且吸附能力不足时，水下沉积物盖对缓解污染物砷迁移可能相对无效。对于汞，硫酸盐的减少促进了生境层以下的辰砂（HgS）的沉淀，并且穿过沉积物-水界面的相关通量很低。因此，盖厚度是关键的设计参数，可以调整以控制硫化汞沉淀在沉积物-水界面下方的深度。在平均孔隙水条件下，最高的溶解甲基汞浓度出现在河口环境的生境层中，但是由于在沉积物有机质上的吸附，预计最高的沉积物浓度发生在淡水环境中。