| Sediment is an important sink and source of nitrogen, phosphorus, heavy metals and otherpollutants in the lake environment. Endogenous sediment pollution load have a significantimpact on lake water, especially in the case of the external source pollution reduction, andreleasing of the potential within the sediment pollution may increase. Sediment-dredging iswidely adopted for removal of contaminated sediment layer. It has been carried out expendingfor many years at home and abroad. However, studies show that not all of the dredging are valid,and the different areas of the lake should be analyzed differently. Laboratory control simulationis necessary before dredging. With the surrounding economic development, eutrophication andheavy metal pollution in Nansi Lake are aggravating gradually. Nanyang zone in the northern ofNansi Lake were polluted worse as a number of major rivers flow into it. In this article, alaboratory experiment was carried out through a six-month incubation of undredged (control) and dredgedcores to study comparatively the effect of sediment dredging on nitrogen, phosphorus and heavy metalsrelease from the sediment between the estuary of Si River and the district in Nanyang Zone of NansiLake. The inter-relationship of metal fractions and their correlation with sediment physicochemical propertieswas studied. And the cycles of nitrogen and phosphorus in newborn surface layer was studied too.The main results and conclusions are as follows:(1) The physical and chemical indicators of sediments in estuary and lake are significantdifferences. The indicators of lake sediments gradually decreases with depth mostly, while anumber of indicators in estuary sediments were relatively close at45cm above with notsignificant changing, but45cm below were increased significantly. There were "inversionphenomenon" in sedimentary sequence between central lake and Estuary.(2) The total content, exchangeable form content, organic and sulfide binding form contentand residual form of Cu, Pb, Cd, Cr and Hg in sediments had positive correlation with sedimentporosity and organic matter and negative correlation with grain size of sediment, while thecarbonate binding form had no significant correlation with them.(3) The physical and chemical indicators of Nanyang lake sediments trended to decreasedwith the depth increasing30cm above, and lower values appear near30cm. Summing up all thephysical and chemical indicators and economic factors,30cm simulation depth of sedimentdredging was more reasonable.(4) The control effects for phosphorus, nitrogen and heavy metals of sediment in30cm dredging are significantly. After static simulation180days in central lake core, dredgedsediment release rate is negative, becoming the sink for phosphorus, nitrogen and heavy metalsof overlying water sinks. Sediment dredging can effectively reduce release potential of NH4+-Nand heavy metals, as sediment organic matter and porosity decreased. The proportion ofphosphorus speciation in the sediments was changed after dredging. LP, Fe/Al-P and org-Pwhich are more easily released were decreased obviously compared with undredged overall,reducing the cycle rate of sediment-water interface phosphorus. There were more better controldredging in30cm on lake than estuary for phosphorus, nitrogen and heavy metals. Whethersediment dredging depth reasonable is critical, as determined improper, there are still likely topromote the release of pollutants. The release rate of phosphorus, nitrogen and heavy metals withdredged higher than the undredged initial, continuing for several days later, the release rate ofdredged core decline rapidly and lower than that undredged.(5)The trend of diffusion fluxes by FICK diffusion law was consistent with the release rateof static culture for nitrogen, phosphorus and heavy metals. But the former closed to theory ofdiffusion more and deviation with static release rate. The F-values of PO43--P and heavy metalsare generally smaller than the R-values, while F-values of NH4+-N is greater than R-values. |
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