Aherne J, Larssen T, Cosby B J, Dillon P J
Department of Environmental and Resource Studies, Trent University, Peterborough, Ontario, Canada.
Sci Total Environ. 2006 Jul 15;365(1-3):186-99. doi: 10.1016/j.scitotenv.2006.02.041. Epub 2006 Apr 17.
Climate-induced drought events have been shown to have a significant influence on sulphate (SO(4)(2-)) export from forested catchments in central Ontario, subsequently delaying recovery of surface waters from acidification. Field and modelling studies have demonstrated that water table drawdown during drought periods promotes oxidation of previously stored (reduced) sulphur (S) compounds in wetlands, with subsequent efflux of SO(4)(2-) upon re-wetting. Although climate-induced changes in processes are generally not integrated into soil-acidification models, MAGIC (Model of Acidification of Groundwater in Catchments) includes a wetland compartment that incorporates redox processes driven by drought events. The potential confounding influence of climate-induced drought events on acidification recovery at Plastic Lake, south-central Ontario (under proposed future S emission reductions) was investigated using MAGIC and two climate scenarios: monthly precipitation and runoff based on long-term means (average-climate scenario), and variable precipitation and runoff based on the past 20 years of observed monthly data (variable-climate scenario). The variable-climate scenario included several periods of summer drought owing to lower than average rainfall and higher then average temperature. Nonetheless, long-term regional trends in precipitation and temperature suggest that the variable-climate scenario may be a conservative estimate of future climate. The average-climate scenario indicated good recovery potential with acid neutralising capacity (ANC) reaching approximately 40 micromol(c)L(-1) by 2020 and 50 micromol(c)L(-1) by 2080. In contrast, the forecasted recovery potential under the variable-climate scenario was very much reduced. By 2080, ANC was forecasted to increase to 2.6 micromol(c)L(-1) from -10.0 micromol(c)L(-1) in 2000. Elevated SO(4)(2-) efflux following drought events (introduced under the variable-climate scenario) has a dramatic impact on simulated future surface water chemistry. The results clearly demonstrate that prediction of future water quality, using models such as MAGIC, should take into account changes or variability in climate as well as acid deposition.
气候引发的干旱事件已被证明对安大略省中部森林集水区的硫酸盐（SO₄²⁻）输出有重大影响，进而延缓了地表水从酸化状态的恢复。实地和模型研究表明，干旱时期地下水位下降会促进湿地中先前储存的（还原态）硫（S）化合物的氧化，随后在重新湿润时会有SO₄²⁻流出。尽管气候引发的过程变化通常未被纳入土壤酸化模型，但MAGIC（流域地下水酸化模型）包含一个湿地模块，该模块纳入了由干旱事件驱动的氧化还原过程。利用MAGIC和两种气候情景，研究了气候引发的干旱事件对安大略省中南部塑料湖（在未来拟议的硫排放减少情况下）酸化恢复的潜在混杂影响：基于长期平均值的月降水量和径流量（平均气候情景），以及基于过去20年观测月数据的可变降水量和径流量（可变气候情景）。可变气候情景包括由于降雨量低于平均水平和温度高于平均水平而出现的几个夏季干旱期。尽管如此，降水和温度的长期区域趋势表明，可变气候情景可能是对未来气候的保守估计。平均气候情景表明恢复潜力良好，到2020年酸中和能力（ANC）达到约40 μmol(c)L⁻¹，到2080年达到50 μmol(c)L⁻¹。相比之下，可变气候情景下预测的恢复潜力大幅降低。到2080年，预计ANC将从2000年的 -10.0 μmol(c)L⁻¹增加到2.6 μmol(c)L⁻¹。干旱事件后（在可变气候情景下引入）SO₄²⁻流出量的增加对模拟的未来地表水化学有显著影响。结果清楚地表明，使用MAGIC等模型预测未来水质时，应考虑气候以及酸沉降的变化或变异性。
