模拟酸沉降对鼎湖山季风常绿阔叶林地表径流水化学特征的影响

通过模拟酸沉降实验,研究了旱季期间(10-3月份)鼎湖山季风常绿阔叶林在4种不同pH模拟酸雨处理(对照、pH 4.0、pH 3.5、pH 3.0)下地表径流水化学输出特征.结果显示:(1)地表径流pH随酸处理强度增强呈“U”型变化模式,酸沉降对地表径流pH的影响不显著(P＞0.05),表明模拟酸沉降尚未引起地表水的酸化.(2)地表径流中NO3-、SO24-浓度随酸处理强度增强略有增加;HCO3-浓度的变化模式与地表径流pH类似.酸根离子浓度与地表径流pH相关性分析表明,SO24-、HCO3-有助于提高地表水抗酸化能力而NO3-则有助于促进地表水酸化.(3)地表径流中盐基离子对酸沉降的响应不尽相同.pH 3.0处理显著提高地表径流中Ca2+、Na+浓度;Mg2+浓度具有随酸处理梯度增强而增加的趋势;K+受模拟酸度的影响小.表明强酸(pH3.0)处理将导致土壤Na+、Ca2+、Mg2+盐基离子流失.(4)酸沉降具有诱发土壤可溶性有机碳(DOC)流失的倾向,增加地表水受有机污染的风险.

Effect of simulated acid deposition on chemistry of surface runoff in monsoon evergreen broad-leaved forest in Dinghushan

The effects of simulated acid deposition on chemical properties of surface runoff were studied in a monsoon evergreen broad-leaved forest in Dinghushan Nature Reserve. Four gradients of simulated acid rain treatments with three replications were designed: control (natural lake water, pH 4.5±0.3), pH 4.0, pH 3.5 and pH 3.0. The surface runoff pH, nitric acid (NO₃^-), sulfuric acid (SO₄^2-), bicarbonate (HCO₃^-), base cations (K⁺, Na⁺, Ca²⁺, Mg²⁺) and dissolved organic carbon (DOC) were detected from October 2011 to March 2012. The result showed that the surface runoff pH was not significantly different among treatments, which exhibited "U" patterns with increasing acid intensity. This suggested the pH was unlikely to decline in a short time. The NO₃^- and SO₄^2- concentrations increased with acid increment, while HCO₃^- exhibited the same pattern as the surface runoff pH. According to the correlation between acid ions concentrations and the surface runoff pH, we found that SO₄^2- and HCO₃^- promoted the ability of anti-acidification, while NO₃^- was adverse. Base cations responded differently to simulated acid treatments. Ca²⁺ and Na⁺ were very sensitive to acid deposition, and their concentrations at pH 3.0 treatment were significantly higher than at other acid treatments. Mg²⁺ concentration increased with the simulated acid intensity, however, there were not significant differences among different acid treatments. K⁺, however, was not sensitive to acid treatment. These results indicated that pH 3.0 treatment led to the loss of Na⁺, Ca²⁺ and Mg²⁺ from the soil. In addition, acid treatments tended to cause dissolved organic carbon (DOC) loss, increasing the risk of organic contamination in the surface runoff.