| Located in northern Jiangxi Province, Poyang Lake is the largest freshwater lake in China as well as one of the important international wetlands of protection. In recent years, with the development of economic society, the pollution of heavy metals in Poyang Lake has increased both in scope and extent. Moreover, associated industries are springing up in urban agglomeration around Poyang Lake, such as photoelectric industry, new energy industry, biological industry, copper smelting and intensive processing industry, the high quality steel products processing industry, petroleum refining and chemical industry, aviation industry, automobile and automobile parts industry, etc. New crucial challenges come when we try to control the level of contamination with heavy metals. Therefore, it is an urgent subject to study the characteristics, impact factors and the maximum capacity in certain environment objective of heavy metals pollution in Poyang Lake.Based on analyzing the water of lake region and main river estuaries as well as the sample of surface sediment and columnar sediment, the content level and space distribution of heavy metals are studied comprehensively. The method of correlation analysis and principle component analysis is applied to further discuss the source of heavy metals. Analysis of the seasonal characteristics of heavy metals in Poyang Lake was combined with hydrology cycle. And health risk assessment model and the potential of the ecological risk index model are applied to evaluate the heavy metal pollution of water and surface sediments, respectively. The main input and output channels of heavy metal within Poyang Lake are analyzed and the corresponding flux calculation method is used to estimate the flux. Take Class II surface water as environmental standard target, the environmental carrying capacity of Poyang Lake is estimated. The main conclusions have been summarized as follows:In the water of Poyang Lake, the content of Fe, Mn, Zn is relatively higher which varied in descending order, while the content of Cu is minimum; Pb, Cu, Zn and Cr have the same pollution source---atmospheric sedimentation; According to the correlation between Cu and Mn, the natural factor is one of the sources of Cu pollution; Besides, Zn and Fe, Cd and Pb, Cu and Zn maybe antagonistic. Principal component analysis shows that, the cumulative contribution rate of the first three principal components is about 78.853%, which could largely reflect the basic source of heavy metals pollution in Poyang Lake Basin:based on the first principal component, Pb, Cu, Fe, Mn show higher positive-load, indicating that the first principal component represents the effect of various pollution sources.In the surface sediment of Poyang Lake, the total average value of seven heavy metals which is Fe>Mn>Zn>Cu>>Pb>Cr>Cd have different degree of changes compare with the situation at the end of the last century. Most heavy metals have the same human homology---industrial waste water, sanitary wastewater and atmospheric sedimentation, except for Fe and Mn which mainly come from the release of dissolved lithospheric mineral. According to the result of principal component analysis, the cumulative contribution rate of the first two principal components---about 70%, could largely reflect the changes of the basic source of pollution:Zn, Cr, Cu, Pb, Cd in the area showed higher positive-load in the first principal component, indicating that the first principal component mainly represents the effect of pollution by human beings; And Pb, in the second principal component, shows a higher positive-load which represents the influence of atmosphere sedimentation; Fe and Mn, with higher load in the third principal component, represent the effect of runoff, rock weathering and natural erosion.In the columnar sediment of Poyang Lake, the average content of heavy metal varies in descending order of Fe, Mn, Zn, Cu, Pb, Cr, Cd as well as in the lake of Du Chang. Take Hukou as an example, the content of heavy metal elements change irregularly with the irregular jagged vertical distribution, but most elements are in an upward trend. The elementary peak appears in different depth, Cr and Cu appeare in-2cm which shows that pollution is serious; Zn, Mn, Cd and Pb appeared in-20cm while Fe appeare in the most shallow layer. Zn, Mn, Cr, Cd and Pb from surface to-32cm are multi-peak sawtooth-shaped, indicating that this period of time within the space, the major pollutants is diversified and has large heterogeneity; While Cu and Fe appeared between-6cm and-18cm which have a relatively stable content, stating that the deposition of Cu and Fe are stable and accept little pollution outside. According to correlation analysis and principal component analysis, heavy metals in columnar sediment mainly come from mining, smelting, discharge of sewage from chemical industries, natural weathering and erosion, atmospheric sedimentation.Heavy metals obviously have seasonal characteristics in Poyang Lake. In the wet period, the concentration of Zn, Pb and Cu is the highest. The maximum value of Cd appears in the normal river flow period. According to the result of health risk assessment, the health risk level is Cd>>zn>Cu>Pb and the health risk of Cd is 2-4 orders of magnitude higher than Zn, Cu and Pb; The heavy risk level in the period ranks as:the normal river flow periodl>dry season>the normal river flow period2>wet period. Heavy metals in Poyang Lake are low harm. Its level of health risk is lower than the maximum acceptable level of risk--- (5.00×10-5a-1) which is recommended by ICRP. After the ecological risk of sediment in Poyang Lake was evaluated, the results show that ecological risk of heavy metal in sediment is also relatively low.The characteristics of heavy metal pollution are the result of natural and man-made factors. As far as natural factor, the water temperature tended to raise, in addition, the adsorption of heavy metal for suspended matter tends to increase in the condition of global climate change. Meanwhile, the eluviation of rain on heavy metal in the tailings will also increase; The effect of intensive rainfall not only increase atmospheric heavy metal wet deposition in Poyang Lake region but as well aggravate urban non-point source pollution and heavy metal pollution in mining area; Strong wind wave action also promote the release of heavy metal in surface sediment through disturbing. As far as man-made factors, the water conservancy project is artificially changing the biogeochemical behavior of heavy metal pollution in Poyang Lake, mining could be a mainly source of heavy metal, the effect of eluviation also make heavy metal from tailings into water. Sand excavation caused the pollution by agitating the sediment. The pollution is exacerbated for the activities and operation of vessels. On the one hand, artificial adjustment reduces the health risks of drinking water, on the other hand, it causes the relatively backward of administrating and controlling, which might make more difficulties in later work.According to the flux of heavy metal, the total inflow flux of Zn, Cu, Pb,Cd is decreasing in order, in general, the flux of suspended heavy metal is lower than the dissolved. Affected by the upper reaches of the river, the flux of heavy metals' inflow among five rivers is dramatically different, the flux of four heavy metals is Ganjiang>Rao River>Xinjiang River>Xiushui>Fu River; The flux of certain kind of heavy metal in five rivers have been analyzed concretely. For the flux of Pb: Ganjiang>Xinjiang>Xiushui>Rao River>Fu River, for Cu and Cd: Ganjiang>Xinjiang>Rao River>Xiushui>Fu River, for Zn:Ganjiang>Rao River>Xinjiang>Xiushui>Fu River; The total flux value varies in the descending order of Zn, Cu, Pb, Cd, which mainly come from fiver rivers. As far as the outflow flux around the year, heavy metals mainly exist in suspended form and the total flux of four heavy metals is Zn>Cu>Pb>Cd.Take ClassⅡsurface water as environmental standard target, based on the result of estimation, the environmental capacity of Pb, Cu, Zn, Cd in Poyang Lake are 0.63t/a,66.86t/a,66.59t/a,0.33t/a, respectively. With obvious seasonal differences, the environmental carrying capacity is wet period>flow period>dry season. The environmental carrying capacity increases first and decreases afterwards around the year which shows a single peak pattern.
|
PDF Full Text Request