Abstract:

Forest ecosystem plays an important role in air purification, interception of pollutants and improvement of water quality. In order to evaluate the interception capacity and regulation characteristics of typical forest ecosystems in subtropical regions to nitrogen, phosphorus and heavy metal ions in atmospheric precipitation, three typical forest stands (evergreen broad-leaved forest, coniferous and broad-leaved mixed forest, and coniferous forest) in Xinfengjiang reservoir area of Guangdong Province were selected as the research objects in this paper. The variation characteristics and canopy interception effects of pH, TP, TN, NH₄⁺-N, and NO₃^--N and six heavy metals (Cd, Cr^{6 +}, Pb, Cu, Hg, and Mn) in atmospheric precipitation, throughfall, stemflow, soil infiltration water and stream water were analyzed. The results showed that during the observation period, the pH of atmospheric precipitation was neutral after the output of the three forest streams, and the evergreen broad-leaved forest had strong buffering capacity for acid rain. The acidification of precipitation after coniferous forest was aggravated, and the pH value of stem flow was 3.89. The concentrations of TN, TP, NH₄⁺-N and NO₃^--N in precipitation were 0.977, 0.046, 0.047 and 0.173 mg?L^-1, respectively. The concentrations of Cd, Cr⁶⁺, Pb, Hg, Cu and Mn were 0.041, 8.05, 0.512, 0.014, 1.31 and 16.9 μg?L^-1, respectively. During the precipitation process, the concentrations of nitrogen and heavy metals mostly increased first and then decreased. The peak concentration was mostly in soil infiltration water, and the Hg concentration showed an increasing trend. The concentration of nitrogen and heavy metal ions in soil infiltration water was extremely high, which may be related to the high background value of nutrients and heavy metals in surface litter and soil. The strong acidity of the acidic soil water environment promotes the precipitation of ions. The atmospheric deposition of TN, TP, NH₄⁺-N, NO₃^--N, Cd, Cr⁶⁺, Pb, Hg, Cu and Mn were 13.3, 0.83, 1.66, 2.59, 0.82, 160.9, 10.5, 0.28, 25.9 and 363.5 g?hm^-2, respectively. The ability of typical forest canopy to adsorb or desorb nitrogen, phosphorus and heavy metal deposition was different. The coniferous and broad-leaved mixed forest and coniferous forest had better interception and purification effect on TN, TP, NH₄⁺-N and Cd, and the interception rate was higher than that of evergreen broad-leaved forest. Evergreen broad-leaved forest canopy produced more nitrogen, phosphorus and heavy metal elements, which could effectively absorb air pollution and improve air quality. The coniferous forest and coniferous and broad-leaved mixed forest canopy can better filter and purify the precipitation water quality than the evergreen broad-leaved forest.

Key words: forest ecosystem, pH value, nitrogen and phosphorus deposition, heavy metals, canopy interception

摘要：

森林生态系统在净化空气、截留沉降污染物及改善流域水质等方面具有重要作用。为评价亚热带地区典型森林生态系统对大气降水中氮、磷及重金属离子的截留能力和调控特征，以广东省新丰江库区3种典型林分（常绿阔叶林、针阔混交林、针叶林）为研究对象，分析了大气降水、穿透水、树干茎流、土壤渗透水及溪流水中pH值、总磷（TP）、总氮（TN）、硝酸盐氮（NO₃^--N）、铵态氮（NH₄⁺-N）及6种重金属（Cd、Cr⁶⁺、Pb、Cu、Hg、Mn）含量的变化特征和冠层截留效应。结果表明：观测期间，大气降水经3种林分溪流输出后，均呈中性，常绿阔叶林对酸雨的缓冲能力较强。降水经针叶林后酸化加剧，树干茎流pH值为3.89。大气降水中TN、TP、NH₄⁺-N和NO₃^--N质量浓度分别为0.977、0.046、0.047和0.173 mg?L^-1，Cd、Cr⁶⁺、Pb、Hg、Cu和Mn的质量浓度为0.041、8.05、0.512、0.014、1.31和16.9 μg?L^-1。降水过程中氮素及重金属浓度多呈先升高后下降的趋势，峰值多现于土壤渗透水中，而Hg浓度呈增加趋势。土壤渗透水中氮素和重金属离子浓度极高，可能与表层凋落物、土壤中养分和重金属本底值含量偏高有关，酸性较强的土壤水环境促进了离子的析出。TN、TP、NH₄⁺-N和NO₃^--N的大气沉降量分别为13.3、0.83、1.66和2.59 kg?hm^-2，Cd、Cr⁶⁺、Pb、Hg、Cu和Mn的沉降量为0.82、160.9、10.5、0.28、25.9和363.5 g?hm^-2。典型林分冠层吸附或解吸氮、磷物质和重金属沉降的能力有所差异，针阔混交林和针叶林对TN、TP、NH₄⁺-N和Cd有较好的截留净化作用，截留率均高于常绿阔叶林。常绿阔叶林冠层析出了较多的氮、磷物质和重金属元素，能够有效吸纳大气污染并改善空气质量；而针叶林和针阔混交林冠层相对于常绿阔叶林能更好地过滤、净化降水水质。

关键词: 森林生态系统, pH值, 氮磷沉降, 重金属, 冠层截留