珠江三角洲马尾松年轮重金属含量年代变化

采用树木年轮化学分析手段,探讨了肇庆鼎湖山(相对清洁区)和南海西樵山(污染区)马尾松(Pinus massonianaL.)不同时期木质部6种重金属(Cu、Zn、Ni、Cd、Cr和Pb)含量的年代变化。结果表明:西樵山马尾松林地表层土壤Cu、Zn、Cd和Pb含量均超过其在广东省表层土壤环境背景值,鼎湖山马尾松林地表层土壤除Cd外其余重金属含量在背景值范围内;鼎湖山和西樵山马尾松木质部中Cu、Zn、Cr和Pb含量均呈现从心材到边材上升的分布格局,反映了珠江三角洲环境中可供植物利用的重金属在过去有了增加。Cu、Zn、Ni,特别是Cr和Pb的最大含量出现在1990年后形成的木质部中,两地环境(土壤和大气)中重金属含量增加是导致马尾松木质部重金属含量上升的主要原因;在相同时期形成的木质部中,西樵山马尾松木质部Cu、Cr和Pb的含量大于鼎湖山,Zn、Ni和Cd含量则小于鼎湖山,这与环境重金属含量差异有关,也与马尾松对不同重金属的富集能力有关。马尾松年轮化学分析的结果能够提供珠三角地区重金属的历史变化信息。

Historical Changes in Heavy Metals in Tree-rings of Masson Pine (Pinus mossoniana) in the Pearl River Delta, South China

Heavy metals (Cu, Zn, Ni, Cd, Cr and Pb) in the tree-rings of Masson pine (Pinus massoniana) growing in Dinghushan (relatively clean area) and Xiqiaoshan (polluted area) were determined in 5 year increments, respectively. Surface soil beneath the sampled trees at Xiqiaoshan elevated concentrations of Cu, Zn, Cd and Pb compared with their background values in Guangdong Province, whereas at Dinghushan, had lowed metal concentrations in the ranges of the background values except Cd. Contents of Cu, Zn, Ni, Cr and Pb increased steadily in tree-rings from the heart-wood to sap-wood at both sites, reflecting the increase in the bio-availability in the Delta area during the past decades. Peaks in Cu, Zn, Ni and most obviously Cr and Pb, were found in rings formed after 1990. It was suggested that the recent increase of the heavy metals in soil and atmosphere in the Delta was the main source contributed to the elevation of the heavy metals in the pine rings. In the rings formed during the same period, content of Cu, Cr and Pb at Xiqiaoshan were constantly higher, whereas Zn, Ni and Cd, consitantly lower than those at Dinghushan, which was not only related to the difference of the metals content in the environments, but also to the difference of accumulation ability of the metals in the pine. The results indicated that tree ring chemistry of Masson pine could provide information concerning historical changes of heave metals in soil and atmosphere in the Delta.