Sedimentation Characteristics And Sources Of Mercury Under The Typical Evergreen Broad-leaf Forest In Mid-subtropical Forest Ecosystem

Mercury-the metal which is liquid at room temperature, due to its high vapor pressure is easy to volatile into the atmosphere. Mercury is one of the most toxic heavy metal pollutants. Gaseous elemental mercury which accounted for more than 90% of the total gaseous mercury can follow the atmosphere for long distance migration, because GEM is stability to stay in the atmosphere for 1 year. All forms of mercury in the atmosphere have experienced the process of moving into the atmosphere, transforming and eventually moving out of the atmosphere, wet and dry deposition is the main way of atmospheric mercury removal from the atmosphere.As the largest ecosystem in the land, the atmosphere is the main source of the mercury of the forest ecosystem. The cycle of Hg in the forest ecosystem is an integral part of the global cycle of mercury. At present, the research on the migration and transformation of mercury in atmosphere and dry and wet deposition of Hg has been carried out at home and abroad, but the relative research on forest ecosystem is still relatively small. Therefore, choose the Chongqing Jinyun Mountain National Nature Reserve as the monitoring points, by measuring the concentrations of total Hg, particle mercury and methyl mercury in the precipitation and throughfall of Mt. Jinyu to analyze the mercury deposition. Through the long-term online monitoring of atmospheric mercury concentration in Jinyun Mountain National Nature reserve, exploring the relationship of mercury deposition and atmospheric mercury pollution in the typical date, and ultimately to explore the relationship between sources and the migration mechanism of mercury under the Typical Evergreen Broad-leaf Forest in Mid-subtropical Forest Ecosystem. In order to provide basic data for establishing the global mercury deposition database, improve the mechanism and model of global biogeochemical cycling of mercury.The results are as follows:(1) The average concentration of THg and Me Hg of Mt. Jinyun in the throughfall and precipitation was the same as local place Gagong and Leigong, but 3times higher than North America. The average concentration of THg was(11.9±7.6) ng·L-1 and the average concentration of Me Hg was(0.20 ±0.013) ng·L-1 in the precipitation. The average concentration of THg was(20.1 ±12.3) ng·L-1and the average concentration of Me Hg was(0.55 ±0.24) ng·L-1 in the throughfall.(2) The average concentration of DHg in the throughfall was higher then that in the precipitation, and the average concentration of PHg in the throughfall was significantly higher than that in the precipitation, The average concentration of DHg was 6.83 ng·L-1 and the average concentration of PHg was 2.97 ng·L-1 in the precipitation. The average concentration of DHg was 7.95 ng·L-1 and the average concentration of PHg was 11.88 ng·L-1 in the throughfall. The percentage of Me Hg accounted for THg was 0%~17.07%, the average value was 3.66% in Mt. Jinyun, which was higher than other regions.(3) During the entire monitoring period(March 2012 to February 2013), the annual concentration of TGM in Jinyun Mountain was(4.71 + 1.92) ng·L-1, which was higher than the northern hemisphere background value1.5~1.7 ng·m-3. Compared with the domestic and foreign background, urban monitoring and the same latitude region, the atmospheric mercury content in Jinyun Mountain is high, that is to say the atmospheric of Jinyun Mountain has been polluted to some degree. The order of the average concentration of TGM in Mt. Jinyun was: summer(June to August) > winter(December to February) > spring >(March to May)> autumn(September to November). Summer and winter TGM concentration fluctuations larger, there was high concentration of DHg and PHg in precipitation and throughfall, the concentration of DHg was 65.5ng·L-1 but the concentration of TGM in April was(4.09±0.71)ng·m-3. This shows that during the monitoring period, the mercury pollution in the surrounding areas of the monitoring points is serious. In July 2012 TGM appears annual maximum(7.05±1.79) ng·m-3, in October 2012 TGM appears annual minimum(3.52±0.83) ng·m-3. TGM concentration in summer is similar in nighttime and daytime, the other three quarters the TGM was higher in the daytime, the four seasons’ TGM concentration have a peak value between 12:00 to 14:00.(4) The Jinyun Mountain is affected by a certain amount of atmospheric mercury pollution from different directions in the four seasons. Mercury source analysis of typical pollution process shows that the high content of particulate mercury pollution in April mainly from the Chongqing and high concentration of atmospheric mercury pollution in July is more likely due to the long distance migration of atmospheric mercury from Guizhou and other regions. The result of backward trajectory analysis using HYSPLIT shows that the main source of the TGM in Simian Mountain mainly comes from the local coal combustion, and long distance transportation by the Indian monsoon may plays a role for the increasing TGM level.