(2.重庆市江津区四面山森林资源管理局, 重庆 402296)
(3.西南大学重庆市农业资源与环境研究重点实验室, 重庆 400716)
【摘要】针对四面山常绿阔叶林中汞的输入/输出量进行了为期1年的监测, 结果显示:四面山大气降雨中总汞 (THg) 和总甲基汞 (TMe Hg) 的浓度分别为 (11.23±2.6) ng/L和 (0.35±0.24) ng/L, 该地区大气降水受到了人为汞污染的影响;大气降水在经过森林林冠层的过程中, 淋溶了沉降在林冠层的大气干沉降, 进而导致林内降雨中的THg浓度升高, 但是林内降雨中的TMe Hg浓度基本保持不变;森林地表径流水中THg的浓度 (4.5±2.0) ng/L相较大气降水明显降低, 说明该森林生态系统对大气降水中的汞具有很强的拦截固定作用.枯枝落叶是该森林生态系统主要的汞输入途径, 其主要通过叶片对大气环境中汞的吸收, 而随着枯枝落叶在地表的积累并分解, 这部分汞被富含高浓度溶解性有机物的表层土壤固定在土壤层中.林地地表/大气界面释汞是该森林生态系统汞流失的主要途径, 地表释汞通量暖季比较大而冷季较小, 其主要受光照、温度、地表汞浓度、土壤含水量等影响.该森林生态系统, 总的汞输入量大于总输出量, 在汞的地球化学循环中起到汇的作用.
【基金资助】 国家“973”项目 (2013CB430003) ; 国家自然科学基金资助项目 (41573105, 41173116) ; 重庆市自然科学基金资助项目 (cstc2016jcyj A1643) ;
Mercury dynamics and mass balance in a subtropical forest in Southwest China
(2.Simian Mountain Forest Resources Administration, Chongqing, China 402296)
(3.Chongqing Key Laboratory of Agricultural Resources and Environment, Southwest University, Chongqing, China 400716)
【Abstract】Forest ecosystem plays an important role in the geochemical cycle of mercury, but it is still not clear which compartment is the major source or sink for mercury cycling in the forest ecosystem. Simian Mountain was selected in our study because it had a subtropical monsoon climate and abundant precipitation ranging from 1 023 mm to 1 586 mm, which is beneficial to the growth of forest vegetation. Moreover, the evergreen broad-leaf forest in Mt. Simian is the most representative vegetation type preserved in the study reserve. Therefore, the input and output of mercury in this forest was monitored for one year. Results showed that THg and TMeHg concentrations in the precipitation were (11.23 ± 2.6) ng/L and (0.35 ± 0.24) ng/L respectively, which were higher than the global background values, probably due to the anthropogenic mercury pollution from ambient cities. The throughfall had higher mercury concentrations than precipitation, which was probably because the precipitation scoured the mercury settled in the canopies by dry deposition. THg concentration [(4.5 ± 2.0) ng/L] in the forest runoff decreased remarkably compared with that in the precipitation, which confirmed that the forest ecosystem had strong interception and fixation effect on mercury from precipitation. The main input pathway of mercury in the forest ecosystem was through litter, because atmospheric mercury can be absorbed by tree leaves. Moreover, when the tree leaves fell on the ground, the mercury in litter was released to the soil during its decomposition. Finally, this part of mercury was accumulated in the top soil due to the high concentrations of dissolved organic matter, leading to higher THg concentration in the top soil. Mercury emitted from the surface forest ground was the main way of output in this forest, which was affected by solar radiation, temperature, mercury concentration in top soil, soil moisture and so on. For the studied forest ecological system, the total amount of mercury input was greater than its total output, so it acted as a “sink” in the biogeochemical mercury cycle.
【Keywords】 mercury; methylmercury; forest ecosystem; Simian Mountain; output/input;
【Funds】 National Basic Research Program of China (2013CB430003); National Natural Science Foundation of China (41573105, 41173116); Chongqing Natural Science Foundation (cstc2016jcyjA1643);
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