酸雨胁迫下樟树林降水中无机阴离子变化特征

Variation of inorganic anions in precipitation in Cinnamomum cam forests

对城市大气降水及城市樟树林穿透水、树干茎流、地表径流中的SO2-4、NO-3、Cl-、NO-2、F-、Br-、PO3-47种水溶性无机阴离子进行了定位测定,Br-、PO3-4未检出;主要的阴离子为SO2-4、NO-3,二者占总阴离子含量比例最大,占到75.6%—89.0%,且在水文学各分量中变异系数均值都很稳定,变动幅度在0.40—0.47;在各分量中SO2-4、NO-3、Cl-、NO-2、F-含量变化较大:大气降水、树干茎流中均为SO2-4>NO-3>Cl->F->NO-2,穿透水为SO2-4>NO-3>Cl->NO-2>F-,地表径流为NO-3>SO2-4>Cl->F->NO-2;穿透水SO2-4、NO-3、Cl-、F-、NO-2淋溶系数分别为3.83、2.61、4.18、4.32、16.06,树干茎流SO2-4、NO-3、Cl-、F-、NO-2淋溶系数分别为7.52、3.55、4.29、2.76、3.10,地表径流SO2-4、NO-3、Cl-、F-、NO-2淋溶系数分别为2.60、4.74、5.00、3.01、3.56,表明阴离子在樟树林水文学过程中均表现出不同程度的富集效应;大气降水中PH均值为4.77,SO2-4/NO-3当量比值为1.1,属于硫酸-硝酸混合型酸雨;大气降水SO2-4、NO-3、Cl-、F-与穿透水中SO2-4、NO-3、Cl-、F-对应呈显著性正相关(P<0.01),大气降水NO-3与树干茎流NO-3呈显著性正相关(P<0.01),地表径流中SO2-4、Cl-与穿透水、树干茎流中SO2-4、Cl-对应呈显著性正相关(P<0.01),说明樟树林能够吸附大气中的酸性物,让酸性养分于自身系统内部吸收、迁移、络合,从而起到净化大气的效用;穿透水p H与地表径流NO-3、NO-2呈显著性负相关(P<0.01),与地表径流SO2-4呈显著性正相关(P<0.05),表明NO-3、NO-2有助于促进地表水的酸化,而SO2-4有利于缓解地表水的酸化;穿透水p H均值5.62,对酸雨起到中和作用,树干茎流p H均值4.61,有被酸化趋势,地表径流p H均值7.19,接近中性。

Changes in 7 water-soluble ions including SO4^2-、NO3^-、Cl^-、NO2^-、 F^-、Br^-、PO4^3- of rainwater were investigated in Camphor forest ecosystems in Changsha city, Hunan Province of China. Water samples were taken as rainfall above the forest canopy, throughfall, stemflow and surface runoff in the forests. The result showed that Br^- and PO4^3- were not detected in all water samples. Both SO4^2- and NO3^- were the major inorganic anions in waters under Camphor forests, which accounted for 75.6-89.0% of the total anion contents in the forest ecosystems. The contents of anion decreased in an order： SO4^2- 〉 NO3^- 〉 Cl^- 〉 F^- 〉 NO2^- in rainfall and stemflow; SO4^2- 〉 NO3^- 〉 Cl^- 〉 NO2^- 〉 F^- in throughfall and NO3^- 〉 SO4^2- 〉 Cl^- 〉 F^- 〉 NO2^- in surface runoff. The leaching coefficients were 3.8, 2.6, 4.2, 4.3 16.1; 7.5, 3.6, 4.3, 2.8 3.1; and 2.6, 4.7, 5.0, 3.0 3.6 for SO4^2-, NO3^-, Cl^-, F^-, NO2^- in throughfall, stemflow and surface runoff, respectively. The pH value averaged 4.77 in rainwater and the ratio of SO4^2-/NO3^- was 1.1 in the study area, which indicated that the rainwater was a sulfuric-nitric mixed acid rain. A significant positive correlation was found between rainfall and throughfall for all anions, except for NO2^-. The NO3^- in rainfall was significantly and positively related to that in stemflow. There were a positive relationship of SO4^2- and Cl^- between throughfall and stemflow and surface runoff. The pH was 5.62, 4.61 and 7.19 in throughfall, stemflow and surface rounff, respectively.Our results demonstrated that Camphor forest ecosystems had a relative high ability to purify acid rainfall through adsorbing, uptaking, leaching and neutralizing processes.