北京城市森林生态系统凋落物汞分布特征及沉降通量

Mercury distribution characteristics and deposition flux of leaf litter in Beijing urban forest ecosystem

大气汞沉降是全球性的环境问题,因其可从城市和工业地区进行远距离传输沉降到偏远地区,并通过食物链富集危害到人类和野生动植物的健康。为了揭示城市森林生态系统中凋落物汞分布特征及沉降通量,本研究选取北京市西北至东南对角线上的公园、街道和居民区3种土地利用类型,收集了29个采样点主要绿化树种的凋落物。结果表明,北京市平均叶凋落物汞浓度为(35.98±14.90)ng·g^(−1);在8个主要绿化树种中,白蜡凋落物汞浓度最高(50.14±31.10)ng·g^(−1),油松凋落物汞浓度最低(12.58±8.69)ng·g^(−1),大部分树种之间存在显著性差异;同一树种在不同土地利用类型中没有显著性差异,但所有树种的平均叶凋落物汞浓度呈现从市中心到郊区下降趋势,说明北京城市森林生态系统中的汞分布受到人为活动影响明显。北京市区森林凋落物汞沉降通量范围是(196.29—438.08)mg·(ha·a)^(−1),北京郊区森林凋落物汞沉降通量范围是(105.98—153.52)mg·(ha·a)^(−1),这些结果为进一步深入评估城市森林生态系统在大气汞循环中的作用提供了基础支撑。

The deposition of atmospheric mercury(Hg)is a global problem,because it can be transported from cities and industrial areas to remote areas through long-distance transportation and endanger the health of humans,wild animals and plants through food chain enrichment.In order to reveal the mercury distribution characteristics and deposition flux of leaf litter in the urban forest ecosystem,this study collected leaf litter samples from 29 sites in parks,streets,and residential areas on the diagonal from northwest to southeast of Beijing.The results showed that the average mercury concentration of leaf litter in Beijing was(35.98±14.90)ng·g^(−1).Among the eight main greening tree species,the highest mercury concentration of leaf litter was(50.14±31.10)ng·g^(−1) from the Fraxinus excelsior,and the mercury concentration of leaf litter in the Pinus tabuliformis Carr.was the lowest((12.58±8.69)ng·g^(−1)).There are significant differences among most tree species and no significant difference was found in the same tree species from different land use.The average mercury concentration in leaf litter showed a downward trend from the city center to the suburbs,indicating that the mercury distribution in Beijing's urban forest ecosystem is significantly affected by human activities.The leaf litter mercury deposition flux in Beijing urban forests are(196.29—438.08)mg·(ha·a)^(−1),and(105.98—153.52)mg·(ha·a)^(−1) for Beijing suburban forests.These results will benefit to the further evaluation of the role of urban forest ecosystems in the atmospheric mercury cycle.