| Comparative study of sediment records located at different distances from pollution sources is of great significance to reveal the source and evolution of regional pollution.By comparing sediment records from Lake Dali and Lake Kulunnao on southeastern Inner Mongolia Plateau,the main sources,evolutionary history and influence mechanism of atmospheric heavy metals over the past two hundred years were investigated.The results show that:(1)The heavy metals in the sedimentary sequences of two lakes can be divided into two groups.One group is Cr,Co,Ni and Cu,with small coefficients of variation and enrichment factors;The other group is Pb,Zn,CD and Hg,whose coefficients of variation and enrichment factors are significantly higher than those of the first group,and the changes are significantly related to socioeconomic development,implying that they have been influenced by anthropogenic factors.(2)The trends in anthropogenic deposition fluxes of Pb,Zn and Cd in two lakes differ significantly from those of Hg,suggesting the existence of different sources of pollution.The earlies atmospheric heavy-metal pollution event in the region was found at the end of the 19 th century,followed by another in the 1930 s and 1940 s.After the founding of the People’s Republic of China,atmospheric heavy metals in the region quickly reached a temporary peak in the 1950 s,a slight decline in heavy metal pollution in the two lakes due to the decline in national economic development in the 1960 s and 1970 s.After the Reform and Opening-up in 1978,the atmospheric heavy metals started to increase rapidly,which was the largest increase in the past 100 years.After entering the 21 st century,Pb in the atmosphere in the region stopped increasing due to the phasing out of leaded gasoline,but Zn and Cd still increased fluctuatingly.Combined with the records of two lakes and backward trajectories,it was found that atmospheric Pb,Zn and Cd in this region were mainly influenced by atmospheric pollution from the southern Beijing-Tianjin-Hebei region;the influence of Guyuan County on Lake Kulunnao gradually began to emerge after 2005.(3)Changes in Hg indicate that the region was very limitedly affected by atmospheric Hg pollution before 1900;the anthropogenic sediment flux of Hg in two lakes gradually increased after 1900;a small peak in Lake Kulunnao occurred in the 1950 s under the influence of the overall development of China.In the next two decades,under the influence of national economic policy adjustment,the anthropogenic sediment flux of Hg recorded in Lake Kulunnao showed a significant decline;and Lake Dali continued to rise under the influence of the former Soviet Union.After the reform and opening up,Hg of the two lakes increased rapidly.The 1990 s saw a decline in Hg in both lakes,mainly influenced by the break-up of the Soviet Union;after 2005,Lake Kulunnao was influenced by the economic development of Guyuan County,and rate of increase in Hg anthropogenic sediment flux accelerated;while rate of increase in Lake Dali was slower.Lake Kulunnao was mainly influenced by Beijing,Tianjin and Hebei,and after 2005,the influence of Guyuan County on Lake Kulunnao gradually increased;while Lake Dali was mainly influenced by former Soviet Union before 2000,and was mainly influenced by atmospheric pollution in Beijing,Tianjin and Hebei after 2000.(4)The evaluation of the potential ecological risk indices of heavy metals in two lakes showed that Cd was at a moderate ecological hazard level,the ecological hazard level of other heavy metals was low,and the comprehensive pollution index(RI)was at a moderate ecological hazard level.In recent years,heavy metal pollution in two lakes has been increasing,which needs to draw the attention of the relevant authorities. |
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