| The sediments in lake where the basin material collected together reflect the natural environment, human activities, evolutionary trends and other information of the lake. Through the research of the lake sediments'geochemistry characteristics, we can rebuild soil erosion, human activities, lake evolution history and the process of lake evolution.Songhua Lake which mainly supplied by the Songhua River, Huifa River, Jiao River and other tributaries is the major fresh water lake in the upstream of the Songhua River. The Songhua Lake is the source of domestic and industrial water in Changchun and Jilin City in JiLin province besides the power generation, flood control, irrigation of agriculture, and other functions. The study about the geochemical characteristics of heavy metals and its evolution trends is important to understanding the law of transportation and transformation of the elements during rock weathering, identifying the heavy metal pollution in Songhua Lake and protecting the ecological environment of the Songhua Lake. The concentration distribution and evolution feature of heavy metals in the sediment of the Songhua Lake were studied scientificly in this article, and the material sources of Cd, Hg and other elements were also investigated.The contents of rock-forming elements in sediment of Songhua Lake: SiO2, Al2O3, Ti, TFeO, Mn, MgO, CaO, Na2O and K2O come up to approximate normal distribution, and Cd, Hg, Cu, Pb, Zn, As, Cr, Ni, Mo, La, Ce and Y come up to approximate lognormal distribution. The coefficient of variation of Cd, Hg is 47.4 and 49.4 respectively. It is higher than other elements.The contents of Cd, Hg in the sediment of Songhua Lake increased gradually from deep to shallow. It represents surface enrichment especially Cd. Generally, the content of Hg showing a rising trend in depth from about 60cm to 22cm, from 20cm to the overall surface concentration decreased, with large range fluctuations.Based on the average sedimentation rate and the calibration of sediment column age of Songhua Lake,it is only a little change in sediment Cd content,about 0.10.1×10-6,which is equivalent to the average of A-layer soil in Jilin area,and also close to the average of soil around the whole country,and the content of Cd decreased slightly only in the late 50's. Before 1983, the content change of Hg in accordance with Cd, but from 1983, the content of Hg increased rapidly, peaked in the mid-90s, and then began to decline by a certain degree of inhibition and fluctuate between the 0.07～0.09×10-6.Based on the gray-system-theory, we put time-series data for 1-AGO (accumulated generating operation), then used GM (1, 1) modeling method make a first order differential equation model.Through systematic research and filter, because the model made by data of Cd, Hg during 2000-2007 have a higher accuracy, one generated mathematical model was built by it as follow:According to the formula we will get value of Cd and Hg, then the data can be obtained ,now the content of Cd in surface sediment of Songhua Lake has exceeded the second standard of national soil environmental quality, the content of Hg was low, no more than the first standar. after reduction of the forecasts of Cd, Hg. Forecast results are that the content of Cd in the surface sediments of Songhua Lake will be close to the national marine sediment first standard, but the content of Hg decreased. So we should focus on the situation of Cd-pollution in Songhua Lake to take measures to prevent the Cd-pollution from increasing.Suspended contents are different in different rivers, and the suspended content of Huifa River is higher. In rivers, contents of metal elements which exist in the form of suspended solids changed obviously, and contents of metal elements in dry season was quite huge. The content of the suspended matter is generally higher in wet period than in dry season.In Songhua Lake suspended solids, the content of Cd, Hg was always higher than the upper reaches of the river into the lake no matter what season it was. It means the lake enriching Cd, Hg, and this has a direct impact on the content of Cd, Hg in Songhua Lake suspended.In major rivers of Songhua Lake upstream, suspended solids removal rate of Huifa River is the fastest, the second are Erdao Songhua River and Toudao Songhua River, and the slowest is Jiao River. The transporting rate of suspended solids of Erdao Songhua River and Toudao Songhua River sharply declined after passing the White Mountain Power Dam. The removal rate and flux in one year of the suspended of Cd and Hg were highest in Huifa River.Atmospheric deposition will induce the elevation of Cd, Hg–content in soil, but the rate of increase is small. Content change of Hg, Cd in Songhua lake sediment is the result of river material handling.In Songhua Lake sediment, the source material of Cd is primarily basin of Huifa River, it may be closely related to nickel smelting of Hongqiling and the discharge of waste and polluted water. The evolutionary trend Cd in Songhua Lake sediments showd that Cd pollution has been growing from the last 60s. The main source of Hg is closely related to gold mining in basin of Erdao Songhua River. The evolutionary trend of Hg showed that the content of Hg topped in the early 90s, and then it decreased with fluctuations in a certain range. The pollution of Hg had been inhibited. |
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