重庆酸雨区缙云山典型林分冠层酸雨淋洗特征

选取重庆缙云山的针阔混交林、常绿阔叶林、毛竹林、灌木林4种典型林分,观测酸性降水过程中林外雨、穿透雨及干流等林内水分转换分量中的主要离子含量变化,分析林分冠层对雨水化学组成的影响,结果表明:(1)降雨中的离子当量浓度大小依次是SO42-＞Ca2+＞ NH4+＞Mg2+＞K+＞Na+＞NO3-;(2)降雨经过林冠层后pH值降低,干流的酸化程度增加最大;(3)降雨经林冠层后离子浓度明显增加(除灌木林),穿透雨中通量增加最大的阴离子和阳离子分别为SO42-(2.19×103～6.47×103 eq·hm-2)和Ca2+(1.41×103～3.39×103 eq-hm-2),离子来源主要为大气沉降和植物分泌物或淋出;(4)同一离子在不同林分的干流和穿透雨中的通量变化不同,反映出不同林分冠层的离子交换性差异.在针阔混交林中,林下降雨净淋溶量大小顺序为SO42-＞Ca2+＞ NO3-＞K+＞NH4+＞Mg2+＞ Na+;常绿阔叶林为SO42-＞ Ca2+＞ K+＞NO3-＞ NH4+＞ Mg2+ ＞Na+;毛竹林为Ca2+＞ SO42-＞ K+＞NO3-＞ NH4+＞Na+＞Mg2+;灌木林为Ca2+＞ NO3-＞ K+＞ Na+＞Mg2+＞ NH4+＞ SO42-.

Canopy Leaching Characteristics of Typical Forests during Acid Rain at Jinyun Mountains, Chongqing

Based on continuous monitoring of precipitation and throughfall in the canopy layer of four typical forests, i.e. mixed coniferous forest, evergreen broad-leaved forest, bamboo forest and shrubbery, at Jinyun mountains in Chongqing Municipality, the change of major ion content in precipitation, throughfall and stemflow was detected, and the characteristics of redistribution and leaching effects of the canopy layer on acid rain were analyzed. The results are as follows. (1) The equivalent concentration of major ions were in the ordered of SO₄^2- > Ca²⁺ > NH₄⁺ > Mg²⁺ >K⁺ >Na⁺ > NO₃^-. (2) The pH value decreased after rainfall passed through the forest canopy, and the stemflow was more acidic compared to throughfall. (3) The maximum concentration of anion and cation are SO₄^2- (2.19×10³ 6.47×10³ eq·hm^-2) and Ca²⁺ (1.41×10³ 3.39×10³ eq·hm^-2) in throughfall. The atmospheric precipitation and plant secretion were the primary ion resources within the study area. (4) The concentration variation of one certain ion varied in different stands, demonstrating the divergence property of canopy exchange within different tree species stands. The crown leaching array of major ions from high to low in mixed coniferous forest is SO₄^2- > Ca²⁺ > NO₃^- > K⁺ > NH₄⁺ > Mg²⁺ >Na⁺, that in evergreen broad-leaved forest is SO₄^2- > Ca²⁺ > K⁺ > NO₃^- > NH₄⁺ > Mg²⁺ >Na⁺, in bamboo forest is Ca²⁺ > SO₄^2- > K⁺>NO₃^- > NH₄⁺ >Na⁺ > Mg²⁺, and in shrubbery is Ca²⁺ > NO₃^- > K⁺ > Na⁺ > Mg²⁺ > NH₄⁺ > SO₄^2-.