The Florida Everglades has one of the most severe methylmercury (MeHg) contamination issues in the USA, resulting from factors including high rates of atmospheric mercury (Hg) deposition and sulfate inputs from agricultural lands. Sulfate loading stimulates microbial sulfate reduction and production of toxic and bioaccumulative MeHg. Controls on regional Hg emissions have been successful in reducing Hg deposition and MeHg production in wetlands in other areas, but this has not been the case for the Everglades as the Hg deposited here appears to come from unknown global sources of emissions. We posit that reductions in sulfate loading to the Florida Everglades can be an effective alternative approach used to reduce MeHg production. This study tested this hypothesis (1) by evaluating temporal trends in MeHg concentrations in response to a reduction in sulfate loading at a site in central Water Conservation Area (WCA) 3 and (2) using ecosystem-scale models to predict the effects of reductions in sulfate loading on sulfate concentrations in surface water and MeHg Risk. At the WCA site, we report a decline in sulfate concentrations (from about 9 mg/L in the late 1990s to levels of < 1 mg/L by 2001) due to changes in water delivery as part of Everglades restoration. Concurrent with the decline in sulfate, declines in MeHg concentrations in surface water and fish and wading bird tissues were observed at this site. These results suggest the efficacy of reducing MeHg production and bioaccumulation in the ecosystem through a reduction in sulfate loading. A previously developed model was used to predict the effects of reductions in sulfate loading (97%, 33%, and 10% reduction scenarios) on sulfate concentrations in surface water and MeHg Risk in the Everglades. The model identified areas of the ecosystem where MeHg Risk is most sensitive to the reductions in sulfate loading. Results show that reductions of > 33% in sulfate loading will significantly benefit the Everglades by reducing MeHg Risk.

中文翻译：

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佛罗里达大沼泽地地区硫酸盐和甲基汞分布的生态系统规模模拟和现场观察：对硫酸盐负荷减少的响应

佛罗里达大沼泽地地区是美国最严重的甲基汞（MeHg）污染问题之一，其原因包括大气汞（Hg）的高沉积率和农田的硫酸盐输入。加载硫酸盐可刺激微生物硫酸盐的还原，并产生有毒和生物蓄积性的甲基汞。对区域汞排放的控制已成功地减少了其他地区湿地中的汞沉积和MeHg的产生，但对于大沼泽地而言，情况并非如此，因为此处的汞沉积似乎来自未知的全球排放源。我们认为，减少向佛罗里达大沼泽地的硫酸盐负荷可以是一种有效的替代方法，用于减少MeHg的产生。这项研究检验了这一假设（1）通过评估MeHg浓度随时间变化的趋势，以响应中央水源保护区（WCA）3站点中硫酸盐负荷的减少，以及（2）使用生态系统规模模型预测减少的影响硫酸盐负荷对地表水中硫酸盐浓度和MeHg风险的影响。在WCA站点，我们报告由于作为Everglades恢复的一部分的供水量的变化，硫酸盐浓度下降（从1990年代后期的约9 mg / L下降到2001年的<1 mg / L）。在硫酸盐减少的同时，在该地点观察到地表水和鱼类中MeHg浓度的下降以及涉禽组织的下降。这些结果表明通过减少硫酸盐负荷来减少生态系统中MeHg的产生和生物富集的功效。使用以前开发的模型来预测硫酸盐负荷的减少（减少97％，33％和10％的情况）对地表水中硫酸盐浓度和大沼泽地区MeHg风险的影响。该模型确定了MeHg风险对硫酸盐负荷减少最敏感的生态系统区域。结果表明，减少33％以上的硫酸盐负荷将通过降低MeHg风险而使大沼泽地区受益。