Distribution And Release Characteristics Of Pollutants In Sediments Of Downstream Nansi Lake And Estuary Of Its Inflows

This study sets the sediment of downstream Nansi Lake and its inflows as the research object, and carries out the research of phosphorus distribution and its chemical forms as well as the phosphorus content of overlying water. The content of heavy metals in the surface sediment were analysed, and then carried out environmental quality and potential ecological risk assessment. The simulation experiments of the heavy metal elements release from sediment were carried out under laboratory conditions. The main results were given as follows:There was no significant regularity in the horizontal distribution of phosphorus species, but there existed obvious variances in contents. Bio-available phosphorus (BA-P), sum of exchangeable P(Ex-P), Al bound P(Al-P) and iron bound P(Fe-P), accounted for 41%～65%of the total extracted phosphorus in the sediments, suggesting a high bio-availability in the surface sedimentary phosphorus. There was large content of bio-available phosphorus in sediment cores, which was mainly consisted of Ex-P and Fe-P. Inorganic phosphorus was the overwhelmingly dominant species in both surface sediments and sediment cores, indicated that sediments in Nansi Lake mainly deposit by inorganic phase. Anthropogenic inputs such as domestic sewage and industrial waster water was the mainly pollution source of the sediments in the research area.The spatial distribution characteristics of heavy metals in sediment of the research area were showed as follows:The content of Fe was high in all samples with its average concentration of 24.20mg/g. The content of Cu gradually increases from south to north of Nansi Lake. There was a large magnitude of changes of the Pb in all samples, which the maximum to the minimum value of 78.21 times. The content of Pb were seriously exceeded the standard among all samples except 8# sampling site. Elements of Mn, Zn, Cd changed in a large scope. Contamination of the Old Canal sampling site was obviously higher than other monitoring sites while contamination of the Dajuan sampling site was lower than other monitoring sites. The seasonal distribution characteristic of Fe, Cu in sediments of Nansi Lake presents in this order March>June>December while Mn presents in the order of June> December> March and Cd, Cr present in the trend of June> March> Decembere. Pb shows the seasonal distribution characteristic in the order of March> December> June.On this basis, three methods were applied to evaluate the pollution of heavy metals in sediment. The results showed that the heavy metals contaminated the superficial sediment Nansi Lake in this order:Pb> Cd> Zn> Cu> Cr> Mn. However, in the whole, the result based on Index of Geoaccumulation (Igeo) and the result of integrate pollution evaluation based on Potential Ecological Risk Index (RI) was different. The pollution was light to moderate based on the value of Igeo while the integrated pollution evaluation results for the high pollution levels.The result of ecological risk assessment based on RI was quite different from the evaluation according to the Sediment Quality Guidelines (SQG) quite different. To evaluate according ecological risk assessment based on RI, the harmful effect on ecology of Cd was greater than Pb in each sampling site, while Mn, Cu, Zn, Cr of the potential ecological hazards were at a very light level. According to the value of RI, the ecological risk level of each sample site was moderate to heavy levels. The evaluation according to SQG showed that Cd in most sampling sites were clean and won't produce toxic to the sediment, but the pollution of Cr was heavily to more heavily polluted level.This study selected Cd, Cu, Pb, Zn to carry out the simulation experiments of the heavy metal elements release from sediment and its result were showed as follows: the release of heavy metals sharply decreased with the increase of pH; and the release of heavy metals was increased with the salt and ionic strength increased; temperature and water turbulence intensity were apparently influence on the release of heavy metals in contaminated sediments. The release kinetics of Heavy metals can be divided into two phases:the rapid release phase and phase to release of balance. Cd, Cu, Pb, Zn release kinetics can be described by pseudo second order kinetics reaction better.