Changes in sulfate (SO₄^2–) deposition have been linked to changes in mercury (Hg) methylation in peatlands and water quality in freshwater catchments. There is little empirical evidence, however, of how quickly methyl-Hg (MeHg, a bioaccumulative neurotoxin) export from catchments might change with declining SO₄^2– deposition. Here, we present responses in total Hg (THg), MeHg, total organic carbon, pH, and SO₄^2– export from a peatland-dominated catchment as a function of changing SO₄^2– deposition in a long-term (1998–2011), whole-ecosystem, control-impact experiment. Annual SO₄^2– deposition to half of a 2-ha peatland was experimentally increased 6-fold over natural levels and then returned to ambient levels in two phases. Sulfate additions led to a 5-fold increase in monthly flow-weighted MeHg concentrations and yields relative to a reference catchment. Once SO₄^2– additions ceased, MeHg concentrations in the outflow streamwater returned to pre-SO₄^2– addition levels within 2 years. The decline in streamwater MeHg was proportional to the change in the peatland area no longer receiving experimental SO₄^2– inputs. Importantly, net demethylation and increased sorption to peat hastened the return of MeHg to baseline levels beyond purely hydrological flushing. Overall, we present clear empirical evidence of rapid and proportionate declines in MeHg export from a peatland-dominated catchment when SO₄^2– deposition declines.

中文翻译：

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泥炭地大气硫酸盐沉积的长期实验控制：甲基汞和相关溶质在溪水中输出的响应

硫酸盐 (SO ₄ ^2– ) 沉积的变化与泥炭地汞 (Hg) 甲基化和淡水集水区水质的变化有关。然而，几乎没有经验证据表明甲基汞（MeHg，一种生物蓄积性神经毒素）从集水区输出的速度随着 SO ₄ ^2–沉积的减少而变化。在这里，我们展示了总汞 (THg)、甲基汞、总有机碳、pH 和 SO ₄ ^2–从泥炭地为主的集水区输出的响应，作为长期（1998 年 - ）改变 SO ₄ ^2–沉积的函数2011），全生态系统，控制影响实验。年度战略目标₄ ^2–实验表明，一半 2 公顷泥炭地的沉积量比自然水平增加了 6 倍，然后分两个阶段恢复到环境水平。添加硫酸盐导致月流量加权甲基汞浓度和产量相对于参考集水区增加 5 倍。一旦停止添加 SO ₄ ^2–，出流水中的甲基汞浓度会在2 年内恢复到添加SO ₄ ^{2–之前的水平。}溪水甲基汞的下降与不再接收实验性 SO ₄ ^{2–的泥炭地面积的变化成正比}输入。重要的是，净去甲基化和泥炭吸附增加加速了甲基汞回到基线水平，超出了纯粹的水文冲洗。_{总体而言，我们提供了明确的经验证据，表明当 SO 4} ^2–沉积减少时，泥炭地为主的集水区的甲基汞输出会迅速且成比例地下降。