| Wetland, formed by the interaction between water and land, is the specialecological environment in the earth. These years, pollution and destruction of thewetland ecological system has become more and more serious due to misuse thewetland resources and lack of protection. As a result, wetland ecological systemprotection and pollution prevention has become the core and hotspot of current wetlandresearch. Sediments are the major environmental elements of the wetland ecologicalsystem, the main accumulation reservoir of nutrients and heavy metals. When theenvironmental condition changed, nutrients and heavy metals will release from thesediments. The sediments become the source of water pollution. Therefore, research onthe pollution of wetland sediments has important scientific significance.Taking the Zhalong Wetland as the research object, and using GIS technique andmany statistic methods, this dissertation systematically analyzes the spatial distribution,sources, controlling factors, and pollution features of nutrients and heavy metals. Inaddition, this dissertation analyzes the biological availability of heavy metals in thesediments, selects plants which are good at absorbing heavy metals, and explores thetransferring model of heavy metals in the sediments and reed. The results can besummarized as followings:The average values of OM，TN and TP were34554,1371, and404mg·kg-1respectively, all above their values in the deep part of the sediments. It indicates thatthere is obvious accumulation by the order of TN> OM> TP. The evaluation ofbiological toxic effect indicates that the sediments have been polluted by nutrients,especially by OM and TN which should be paid attention to.The analysis of speciation of N and P indicates that TN mainly exists as Org-N.The concentration of IP is relatively higher than OP, both has almost the equal share ofTP. Their spatial distributions were distinctly different. The concentration of nutritivesalt in the north was higher than that in the south and the west was higher than the east.The high value zone of OM and TN is in the southeast and the high value zone of TP isin the northeast. Org-N, OP and OM have significant correlations. They have similarspatial distribution. The high value zone is in the southwest. While IP is different fromOP, the high value zone of IP is in the northeast. The coupling analysis of C, N and P shows that OM and N have the same sourcewhich is from aquatic biology and land input. N and OM have different source. In thesouthwest area and partial core zone, N/P is bigger than10. And the concentration of Nand P are high. These areas have big potential of eutrophication. In order to controleutrophication, it should cut the concentration of N, and put the concentration of P in areasonable scale. In the north part, it should pay attention to the concentration of N. Inthe other hand, the risk of entrophication in the south part is still relatively low.The concentrations of Hg, Cd, As, Cu, Pb, Zn and Cr were0.065,0.198,10.26,18.20,21.35,52.08and46.47mg·kg-1respectively, which were all above the soilbackground values of Songnen Plain. Their spatial distributions were distinctly different.Except Pb and Hg, Cd、As、Cu、Cr and Zn are mainly from industrial and agriculturalwaste water. The concentration of heavy metals in the north was higher than that in thesouth, and the east was higher than the west. And in the core zone, the concentrationwas relatively low. Particularly in the eastern region, the concentrations of Hg and Cdwere extremely high which should be treated as the major heavy metal pollutionprevention sites.The dominant proportion of Pb, Zn and Cr were in the residual fraction, suggestingthat they were environmental stable. The concentrations of Cu and Hg in the reduciblefraction were relatively high, indicating they had greater environmental effects. Thespeciation of heavy metals is related with not only the total quantity, but also thephysical and chemical features of the sediments such as pH and OM. Except for As, theconcentration of oxidizable fraction of heavy metals has significant correlation with OM.Currently the trend of salinization (of soil) in the wetland is becoming serious, meaningthat the risk of heavy metal release becomes bigger, which should be gain enoughattention by the local authority.The level of pollution of the7heavy metals in the sediments is different based ontwo different evaluation methods. Cd belongs to middle-serious pollution. Hg belongsto light-middle pollution. And As、Cu、Pb、Zn、Cr belong to none-light pollution. Ingeneral, the ecological risk of the heavy metals and metalloid by zone wereexperimental zone> buffering zone> ecological tourism zone> core zone.Among all the plants, reed, bulrush, bald weeds and edible amaranth haverelatively better ability of absorbing heavy metals. Their root is better than their leaf to absorb heavy metals. Especially for edible amaranth, its root has best absorbing ability. Iuse the multiple regression analysis to simulate the quantitative relations betweentransferring accumulation, biological availability, and speciation distribution and thesoil physical and chemical features. The result indicates that the transferring model ofreed heavy metal is log-linear model. The model has a better simulation result to Cd、Hg、Cu、Pb and Zn. However, it is weak to simulate As. The log-linear transferring model ofthis research can predict the accumulation of heavy metals in sediments-reed system. Inthe meanwhile, the model still has disadvantages, which should be put into futureresearch agenda. |
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