Study On Phytoremediation Of Heavy Metals In Dredged Hongfeng Lake Sediments

With the development of social and economy, most of the lakes in our countries affected to different degrees of pollution. The pollution of heavy metals in lake sediment became the important factor which has affected the lake water quality. Although the dredged sediment, as a kind of effective treatment of the water ecological environment recovery method, due to it was piled up may cause secondary pollution of soil and groundwater in the process of dehydration. so the reasonable disposal of dredged sediment is particularly important.As one of the effective methods for pollution dredged sediment treatment, phytoremediation technology has been obtained more attentions recently, mainly for its low cost, friendly to the environment.Hongfeng Lake is one of drinking water resources for Guiyang City. It is playing an important role in the process of social and economic development. Studies have reported that there is a certain degree of heavy metals pollution in Hongfeng sediments and indicated potential hazard to humans and aquatic ecosystems. Due to forage grass had good adaptability, fast growing, large biomass, good resistance and strong soil stabilizing. Meanwhile it had certain ability to absorb and tolerate the heavy metals.Those made it became a hot research subject in Using plants to remedy heavy metals polluted dredged sediments of lake. So this paperchose Hongfeng sediments as research object, a pot experiment in natural environment was conducted to study the phytoremediation efficiency of Lolium perenne, Medicago sativa, Festuca arundinacea, Trifolium pretense, Cichorium intybus, Purus frumentum, Sorghum bicolor×S.Sudaanense to heavy metals contaminated dredged sediments of Hongfeng lake.After planting coatinuous stubbles Lolium perenne, the characteristics of its absorption and transportion of heavy metals in the sediments and rhizosphere effect of Zea mays. At the same time, effects of different concentrations of EDDS on the plant absorption of heavy metals. In order to provide the scientific basis and theoretical basis for plants to remedy heavy metals contaminated dredged sediments of Hongfeng lake. It also provides the other lakes, rivers dredging sediments of phytoremediation with experiences that can be referred to. After the research work,the following conclusion was got:(1) A pot experiment was conducted to study the phytoremediation of seven kinds of plants to heavy metals compound contaminated dredged sediments of Hongfeng lake and select the suitable plants.The result showed Lolium perenne, Medicago sativa, Festuca arundinacea, Trifolium pretense, Cichorium intybus could germinate and grow in Hongfeng lake sediments and accumulation and tolerance of heavy metals were different in this five plants.The concentration of Pb, Cu, Cr in the Lolium perennewere the highest. The concentration of Zn, Ni in the Festuca arundinacea were the highest; The bioaccumulation factor of Cd in Cichorium intybus, Lolium perenne, Festuca arundinacea, Medicago sativa were higher than one, which suggested that they were Cd accumulator plants species; The translocation factor of Lolium perenne, Festuca arundinacea and Cichorium intybus were higher than one, which showed they had high endurance to Cr, Zn and Cd, espectively. All in all, the ability of Lolium perenne and Festuca arundinacea to repair heavy metals in Hongfeng dredged sediments was higher than other plants. It suggested that these two kinds of forage plants had potentials in phytoremediation of heavy metals in Hongfeng dredged sediments.(2) To explore the influence on the same plants to repair heavy metals in Hongfeng dredged sediments by different planting patterns. Planting three stubbles Lolium perenne was conducted. The results showed that the accumulated amounts of heavy metals in the first crop shoot was greater than the second crop, the second crop greater than the third crop.After planting three crops, Lolium perenne absorded the amount of heavy metals in the roots was greater than the amount of in the shoots. The concentration of heavy metals in Hongfeng dredged sediments was reduced. The content of Zn, Cu, Cr from original sediments to first crop andsecond crop sediments were declining obviously. But from second crop sediments to third crop became mild.After three crops, the concentration of Pb, Cd, Ni in the dredged sediments decreased a little.(3) In order to find the influence on rhizosphere effect in phytoremediation processes. The investigations were conducted on the number of microbes and enzyme activities from rhizosphere soils.The results of rhizosphere effect of Zea mays presented that the number of microorganism increased and bacteria in the rhizosphere sediments increased significantly.It was 5.22 times of non-rhizosphere sediments; The activities of urease and alkaline phosphatase increased. The activity of urease increased more obviously.(4) A pot experiment was conducted to explore the influence on different concentrations of EDDS on the plant absorption of heavy metals. The results showed that low concentration of EDDS had no significant effect on Festuca arundinacea growth. With the increase of concentration, the biomass of Festuca arundinacea reduced.It exhibited the toxicity of EDDS for Festuca arundinacea increased obviously, and especially for the roots at high concentration. Compared with not adding a chelating agent processing in the late growth stage, added low, medium and high three levels(1 mmol/kg,5 mmol/kg, 10 mmol/kg) of EDDS made the p H value of the sediment had no significant change.The amount of microorganisms increased.The activity of urease increased obviously and Alkaline phosphatase activity increased slightly; The accumulation quantity of Zn, Cu, Pb, Cd, Ni, Cr in the shoots and roots of Festuca arundinacea increased. And the 5 mmol/kg of EDDS effect was the most significant.