The Effect Of Migration Regulation On Forest Canopy Leaching To Heavy Metal Pollution In Liquidambar Formosana Plantation

Liquidambar Formosana is one of the main forest tree species in south of China. It is a beautiful landscape tree since its leaves are green in spring and summer, and red in autumn. The experiment took an observation on Liquidambar Formosana plantation for one year in Changsha Tian Jiling forestry centre. This paper systematically studied the impact of leaching effect of canopy layer on concentrations and input of heavy metal in the plantation, which could provide theoretical evidence for not only Liquidambar Formosana management and forestland productivity maintainance, but also for the scientific management of forest resource.The results showed that in the whole year, the total rainfall was 1550.1mm, and the net precipitation inside the forest was accounted for 80.18%, the total rainfall that was intercepted by canopy was accounted for 19.82%, the throughfall inside the forest was accounted for 77.38%, stemflow was only accounted for 2.79%. Both throughfall and stemflow had good positive linear relationship with outside-forest precipitation. Meanwhile, canopy interception and outside-forest precipitation had some associations, though they were not as close as the previouse one. In different seasonal,large fluctuations were found in outside-forest rainfall, the highest precipitation was occurred in summer and the lowest one was in winter. The highest throughfall rate was observed in winter and the lowest one was in summer. The highest stemflow rate was found in autumn and the lowest one was in winter. The highest canopy interception rate was observed in summer and the lowest was in winter. Throughfall, stemflow and canopy interception were increased by the rainfall increasing, and the average throughfall and stemflow rates were also increased by the rainfall increasing. However, the average canopy interception rate was decreased along with the precipitation increasing.There had some little changes in pH values of outside-forest rainfall, throughfall and stemflow. The pH changed not very much between seasons except that dropped obviously in winter. In all waters, the average pH values from low to high was:winter, autumn, spring, and summer; the pH value was raised with rainfall increasing in rainfall reassign process, but the degree was not so great.The highest element mass concentration of outside-forest rainfall and throughfall was Zn, and the lowest two were Cu and Pb. In stemflow part, the highest one is Mn and the lowest one was Pb. In outside-forest rainfall part, the order of mass concentrations of heavy metal elements was:Zn>Fe>Mn>Cu>Pb. In throughfall and stemflow, Cu and Mn showed a raise trend, and the most increment was achieved by Mn; Fe, Zn, and Pb showed a decrease trend, and Zn showed the most reduction. Considerable element mass concentration changes were observed among months, which represented as lower values in the rainy season and higher values in the dry season. In all waters, concentrations of heavy metal reduced obviously by the precipitation increasing. Concentrations of heavy metal had little changes among seasons; they were higher in autumn and winter, and lower in spring and summer. Pb was not detected in the winter precipitation. Concentrations of Fe, Zn and Mn had significant differences (p<0.05) among outside-forest rainfall, throughfall and stemflow. However, the difference between Cu and Pb were not distinct.In the whole year, the total input of five heavy metal elements were 30.580 kg·hm-2,6.013 kg·hm-2, and 0.194 kg·hm-2 in outside-forest rainfall, throughfall and stemflow separately. In inside and outside forest rainfall, the amount of heavy metal input changed with months, which represented as high values in rainy seasons and low values in dry seasons. Input of heavy metal elements increased with rainfall increasing. Seasonal input of waters showed that the highest input of Cu and Fe were in spring, the highest input of Zn and Pb were in summer, the highest input of Mn was in autumn; the lowest input of Cu, Fe, Zn and Mn were in winter, the lowest input of Pb was in autumn. Pb was not detected in the winter. The leaching volume of Cu and Mn were positive, and Fe, Zn, Pb were negative, which demonstrated that Cu and Mn that covered on the surface of Liquidambar Formosana were washed out by the rain, and Liquidambar Formosana adsorpted all the Fe, Zn and Pb in the rainfall.