中亚热带典型林分不同层次降水的水质变化特征

Precipitation Levels of Typical Forest Stand in Mid-subtropical Zone:Variation Characteristics of Water Quality

为全面调查亚热带森林生态系统各层次降水水质状况,于2013年9月—2014年8月对重庆市缙云山常绿阔叶林大气降雨、林内降雨、地表径流、土壤渗滤液进行了持续1年的水质效应研究。结果表明:缙云山全年大气降雨明显偏酸性(pH 4.75);土壤层和林冠层均能调升降雨的pH值,其中土壤层对pH值的调升幅度最大,其次为森林冠层;森林林冠层对NO_3^-、NO_2^-、Na^+有一定的吸附净化作用,降雨能够淋溶森林林冠层的NH_4^+、SO_4^(2-)、PO_4^(3-)、Mg^(2+)、Ca^(2+)、K^+;另外,枯枝落叶的降解导致构成植物组织的有机物降解为无机物进而促使各离子浓度在地表径流中增加;森林土壤中的官能团以及胶体能够吸附中和渗滤液中的NO_3^-、SO_4^(2-)、NH_4^+、PO_4^(3-)、K^+、Mg^(2+),同时长期处于酸性条件下的土壤层也释放出了部分Na^+、NO_2^-、PO_4^(3-)、Ca^(2+);重金属铅(Pb)、镉(Cd)在该区域大气降雨中的含量较高,经过森林冠层后表现出大幅下降的趋势,说明森林冠层对有害重金属Pb、Cd有较强的拦截净化作用。

To investigate water quality at different levels of subtropical forest ecosystem,we studied water quality effect of precipitation through fall,runoff and soil leachate of evergreen broad-leaved forest in Jinyun Mountain,Chongqing from September 2013 to August 2014. The results showed that： the precipitation of Jinyun Mountain was obviously acidic （pH 4.75）; the soil and canopy could elevate the pH value of precipitation,and the soil layer had the biggest up-grading of the pH value,followed by forest canopy; forest canopy layer had certain adsorption effect on NO_3^-、NO_2^- and Na~＋,the NH_4~＋、SO_4^（2-）,PO_4^（3-）,Mg^（2＋）,Ca^（2＋） and K~＋ on forest canopy could be leached by precipitation; in addition,the inorganic and organic matter produced by the litter degradation increased ion concentration in surface runoff; functional group and colloid in forest soil could adsorb and neutralize NO_3^-,SO_4^（2-）,NH_4~＋,PO_4^（3-）,K~＋,Mg^（2＋） in leachate; at the same time,forest soil under acidic condition for a long term could release part of the Na~＋,NO_2^-,PO_4^（3-） and Ca^（2＋）; the contents of heavy metal lead（Pb） and cadmium （Cd） were relatively high in the atmospheric rainfall in the area,but showed a dramatic drop after going through the forest canopy,indicating that the forest canopy had stronger intercept purification effect on heavy metals such as Pb and Cd.