城市蒙古栎人工林对降雨中金属元素迁移的影响

Effects of Urban Quercus mongolica Plantation on Transformation of Metal Elements in Rainwater

在位于哈尔滨市区的东北林业大学城市林业示范基地蒙古栎(Quercus mongolica)人工林中心区域设置10 m×10 m观测样地,于2015年5—10月份的树木生长季期间,在距离样地150 m处布设翻斗式雨量计(HOBO RG3-M)和3个自制雨量筒测定大气降雨量(作为对照)、在样地内十字交叉布设13个自制雨量筒测定样地穿透雨量、选取5株蒙古栎作为标准观测样木测定样地树干茎流量;将采集的大气降雨、穿透雨、树干茎流样品,使用0.45μm微孔滤膜过滤,经硝酸酸化处理后,应用火焰原子吸收分光光度计(Thermo Scientific ICE-3500,美国)测定样品中K、Ca、Na、Mg、Cu、Fe、Zn、Mn金属元素质量浓度;分析城市蒙古栎人工林伴随降雨分配过程中的金属元素变化特征和输入规律。结果表明:①大气降雨、林内穿透雨、树干茎流中,8种金属元素质量浓度各不相同,但均为树干茎流金属元素质量浓度大于穿透雨金属元素质量浓度;除K、Na元素外,其他6种金属元素的质量浓度,在降雨分配中由大到小依次为树干茎流、穿透雨、大气降雨,即降雨穿过冠层后,金属元素质量浓度增加。②生长季内8种金属元素的净输入量(林内穿透雨+树干茎流-大气降雨)不同,其中K、Ca、Cu净输入量,分别为-1.382、-1.200、-0.031 kg·hm^(-2);Na、Mg、Fe、Mn、Zn净输入量,分别为0.382、1.631、0.254、0.138、0.011 kg·hm^(-2)。③蒙古栎人工林对8种金属元素总体呈现出截留作用(净输入量为-0.197 kg·hm^(-2)),且受K、Ca、Mg净输入量的影响较大。

In order to explore the effect of the forest ecosystem on the transport of metal elements in rainwater,and understand the biogeochemical cycle process in the urban forest ecosystem,we chose the Quercus mongolica plantation in the Urban Forestry Demonstration Base of Northeast Forestry University in Harbin City as the research object.During the 2015 growing season(May-October),a 10 m×10 m observation plot was set up in the central area of Q.mongolica plantation and thirteen self-made rain gauges were set up in the cross of the plot to measure the throughfall of the plot,and five Mongolian oak trees(Quercus mongolica)were selected as standard observation samples to measure the stem flow of the plot.A tipping bucket rain gauge(HOBO RG3-M)and three self-made rain gauges were set up at a distance of 150 m from the observation plot to measure bulk precipitation(as control check).The samples of bulk precipitation,throughfall and stemflow were collected and filtered by 0.45μm microporous membrane.After acidification with nitric acid,we investigated the contents of K,Ca,Na,Mg,Cu,Fe,Zn and Mn in bulk precipitation,throughfall and stemflow by flame atomic absorption spectrophotometer(Thermo Scientific ICE-3500,USA),and analyzed the variation characteristics and input rules of eight metal elements in the process of rainfall distribution.The results show that:(1)The mass concentration of eight metal elements were different in bulk precipitation,throughfall and stemflow,and the mass concentrations in stemflow were higher than in throughfall.Except for K and Na elements,the mass concentrations of the other six metal elements in the rainfall distribution from large to small were stemflow,throughfall and bulk precipitation,indicating that after the rainfall passes through the forest canopy,the contents of the six metal elements in rainwater increased.(2)Over the growing season,the net inputs(throughfall+stemflow-bulk precipitation)of the eight metal elements were different.The net input of K,Ca,and Cu were-1.382,-1.200 and-0.031 kg·hm^(-2),respectively,and the input of Na,Mg,Fe,Mn and Zn were 0.382,0.254,0.138,and 0.011 kg·hm^(-2),respectively.(3)The net input of eight metal elements in Q.mongolica plantation over the growing season was-0.197 kg·hm^(-2).The Q.mongolica plantation exhibited an interception effect on eight metal elements,and was greatly affected by the net input of K,Ca and Mg.