Speciation And Release Behavior Of Iron And Manganese In The Sediments Of Wangquan Reservoir, Qingdao

With the acceleration of industrialization and urbanization process, internal pollution in sediments has been one of the most important environmental problems that affect the water resources and human life. There exists tightly and strongly interaction between sediment and water column. So it is vital and significant to research on the distribution, chemical forms and release characteristics of internal pollutants and further to control and reduce these pollutants. Based on a large number of domestic and foreign literature, the pollution characteristics, ecological risk and release rules of nutrients, iron and manganese in Wangquan Reservoir sediments were studied comprehensively and systimatically by the means of long-term field monitoring, laboratory experiment analysis and static simulation and multivariate statistical analysis.The main research includes:the temporal and spatial distribution of nutrients, iron and manganese; the correlation between each index; the form characteristics and ecological risk assessment of iron and manganese; the analysis of release rules under different environmental conditions. The main results and conclusions of this study are listed as follows:1. On the whole, the nutrients, iron and manganese average contents in the surface sediments of downstream sections near the Wangquan Reservoir dam are slightly higher than those of upstream sections. The pollution is more serious on the middle thread of reservoir than nearshore. The contents of TP and Mn change with water season, while there are little variations on TN, organic matter and Fe. Moreover, Mn has an obvious seasonal release features.2. The correlation between nutrients and heavy metals suggest:there is a significant linear relationship between Fe and Mn and a strong correlation between organic matter and other pollutants; the average particle size of the sediments themselves has a good negative correlation with TN, Fe, Mn and water capacity, but water capacity shows a significant positive relation with TP, TN, OM, Fe and Mn. In the interstitial water, the concentrations of TN, NH3-N and Mn performs a good positive correlation with the total contents of TN, Fe and Mn in sediments, and a negative correlation with the physical and chemical indicators of overlying water.3. The results of seasonal analyzing forms of iron and manganese in surface sediment of Wangquan reservoir shows that:the main fractionation of iron and manganese is residual form and sulfide-organic-bound form, respectively. The contents change of iron’s carbonate-bound and sulfide-organic-bound form is basically same as manganese’s, which decrease in lower water season(2012.3) while manganese’s increases. In contrast to that the content of manganese’s exchangeable form is higher in common water season(2011.11), the content of iron’s is higher in winter.4. The data of assessing the heavy metal pollution from two perspectives of the total content and each forms content of iron and manganese are compared. All results show that the danger of manganese in Wangquan reservoir surface sediment is greater than iron. But some results are opposite:the manganese pollution is less serious on the middle thread of reservoir than nearshore, and it is more serious in lower water season than in common water season on the middle thread of reservoir.5. In order to clarifying the exchange of contaminants on the sediment-water interface, static laboratory experiments are performed, which, to some extent, reflect the release behaviour of sediment pollutants when environmental conditions change. The results indicate that:iron, manganese and organic matters can release to overlying water easily in the neutral pH and anaerobic conditions; the concentration of dissolved oxygen has no obvious effect on Mn; but the release of phosphorus is promoted under alkaline conditions due to its forms; higher temperature could further promote the release flux of manganese and iron; high DO and pH value has more effects on the release of Fe, while temperature has more significant impact of the release of Mn.