| Heavy metal pollution has been increasingly concerned as the hotest research point by the world. Water environmental quality has been seriously worsened by the large number of heavy metals input from various sources. Heavy metals are inorganic pollutants, of great toxicity, difficult to be degraded, easily enriched in the organism and would cause chronic influence on biologies. Therefore, to research the characteristics and to evaluate the influence of heavy metals in the water is of great significance. In this study, Pengxi River, one tributary of Yangtze River in the Three Gorges Reservoir, was selected as the study area, the water and sediment samples were collected to determine the content and fractional characteristics of six metal elements including Fe, Mn, Cr, Pb, Cu and Cd. Moreover, the simulation experiments were conduceted in the laboratory to research the influence of water level fluctuation on migration and transformation of heavy metals in the sediments, and the effects of Cd release from sediments on the growth of algae in water body. The primary conclusions from the present study are as follows:①Contents of heavy metals in water of Pengxi River in the low water season were higher than those in the normal river season and aboudant season, and kept stable in the normal river season. Generally, heavy metal contents were ordered as Fe > Mn > Cu > Cr > Pb > Cd. Only two elements contents of heavy metals(Pb and Cu) in the low water season exceed the class II and calss I limit of the Environmental Quality Standards for Surface Water(EQSSW) of China, respectively.②Contents of heavy metals in sediments were ordered as Fe > Mn > Pb > Cu > Cr > Cd. Content values of element Cu had a maximum variation coefficient, indicating much serious effect of human activities on this metal than other heavy metals. For the fractions of these six heavy metals studied, Cr, Pb and Cu mainly existed in the residual fraction, with less harmness to the environments. According to the analytical result of Geo-accumulation Index(I-geo) Method, sediments were found to be polluted by three elements of Cd, Pb and Cu.③The simulation experiment of water level fluctuation showed that, the order of heavy metal contents in sediments submerged under water was Fe > Mn > Pb > Cr > Cu > Cd, and the I-geo values indicated the heavy metal pollution degree order was Cd > Pb > Mn > Cu > Cr > Fe. When the water level declined half, heavy metal contents in sediments exposured aerially were in the order of Fe > Mn > Pb > Cr > Cu > Cd, and the pollution degree order was Cd > Pb > Mn > Cu > Cr > Fe according to the calculated I-geo values. Research also showed that the content of heavy metals in sediments reduced after the occurance of the water level fall, and chemical fraction order of metal element Cr, Pb and Cu remained the same.④The simulation experiment of Cd release from sediments showed the N/P ratio of overlying water was over 100, indicating strong eutrophic conditions and phosphoru being a limit factor for the growth of algae. For the overlying water samples without shading, the ensemble downtrend of total algae and the chlorophyll a(Chl a) was similar to the trendency of total nitrogen and total phosphorus content. While the algae difficultly grew and reproduced for the shaded samples, and the content of nitrogen and phosphorus was increased. The correlation analysis of Cd, total algae and Chl a showed that there was weak correlation or antagonism among them, and Cd stimulated the growth of some alage in water. |
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