四川盆地地表水酸化现状与趋势

2009～2011年间对四川盆地地表水的酸化现状进行了一次大规模调查.通过对采集的90多个地表水样的pH和主要阴阳离子浓度的分析发现,除了重庆铁山坪溪流的pH低于6.0,万州开县天蛾池、重庆铁山坪溪流和峨眉山金顶池塘等少数地表水的酸中和容量(ANC)低于0.200mmoleL1,从而表明这些地表水体可能已经发生严重酸化之外,其他水体均具有较高的pH和ANC,表明在四川盆地地表水酸化可能并非严重的区域环境问题.这里存在30多年的严重酸沉降污染,部分水体与20多年前的调查结果相比存在明显的酸化趋势,表现为ANC显著下降,同时SO42和NO3浓度显著升高.SO2和NOx排放的增长是地表水酸化的原因,其中SO2的贡献更明显.四川盆地广泛分布的紫色土具有较高的化学风化速率,是地表水具有较强的酸中和容量的原因.而在周边山地分布着黄壤等风化速率较低的土壤类型,严重的酸沉降可能导致个别地表水的酸化.

Current state and trend of surface water acidification in Sichuan Basin

A regional survey of surface water acidification in Sichuan Basin was carried out during 2009–2011. Analysis of more than 90 samples revealed high pH and acid neutralizing capacity (ANC) in most surface waters, indicating that surface water acidification might not be a serious environmental issue in Sichuan Basin. However, some acidified surface water systems were present. Comparison of the results with a survey conducted 20 years ago revealed a significant decrease in ANC and increasing sulfate (SO42 ) and nitrate (NO3) concentrations. Rapid increases in sulfur dioxide (SO2 ) and nitrogen oxides (NOx ) emissions were likely the primary cause of surface water acidification, while high weathering of the purple soil in Sichuan Basin likely enabled strong buffering against acidification of surface water. However, low weathering occurred in areas of yellow earth and yellow-brown earth in the surrounding mountains, indicating that serious acid deposition could lead to acidification of surface water in these areas.