Study On The Remediation Effect And Mechanism Of Cd And Pb Polluted Sediments In Nansihu Lake

Nansi Lake is an important storage lake for the east route of the South-to-North Water Diversion Project.After the 1970s,with urbanization and industrial development,a large amount of heavy metal pollutants were discharged into the lake,and heavy metals were deposited in the bottom mud in the form of sediments.Heavy metals have become an important threat to water quality due to their extremely high toxicity and hard-to-degradability.The remediation methods of heavy metal contaminated sediment are mainly physical remediation,chemical remediation and phytoremediation.Phytoremediation has become a widely used heavy metal repair method due to its low cost and environmental friendliness.Alternanthera philoxeroides is an aquatic plant widely distributed in the basin of Nansi Lake.It has the characteristics of large biomass,fast reproduction speed and strong resistance to stress.Therefore,this study selected Alternanthera philoxeroides and studied the effects of Alternanthera philoxeroides through laboratory planting experiments.The enrichment performance of Cd and Pb,the influence of Cd and Pb on the growth indexes of Alternanthera philoxeroides,the changes of active oxygen content,antioxidant non-enzyme content and antioxidant enzyme activity in Alternanthera philoxeroides are analyzed,and the effect of Alternanthera philoxeroides on Cd The enrichment mechanism of Pb provides technical support for the remediation of Cd and Pb polluted sediments in Nansi Lake.The results of this study are as follows:(1)There are differences in the effects of different concentrations of heavy metals on the growth indicators of Alternanthera philoxeroides.With the increase of Cd and Pb concentration,the increase in fresh weight and root length of Alternanthera philoxeroides showed a trend of first increasing and then decreasing,while the increase of plant height showed a downward trend.A small amount of Cd and Pb can promote the increase of plant fresh weight and root length.High concentration of Cd and Pb can inhibit the increase of fresh weight,root length and plant height.When the concentration of Cd and Pb is 0.8mmol/L and 2.0mmol/L Compared with the control group,the increase in fresh weight of Alternanthera philoxeroides decreased by21.8%and 19.8%,the increase in plant height decreased by 44.2%and 54.3%,and the increase in root length decreased by 33.5%and 42.3%.With the increase of Cd and Pb concentrations,the content of photosynthetic pigments in plants showed a downward trend.Chlorophyll a/chlorophyll b increased first and then decreased with the concentration of Cd and Pb.When the Cd and Pb concentrations were 0.05mmol/L and 0.2mmol/L,chlorophyll a/chlorophyll b reached the maximum,and then decreased,indicating that the chlorophyll a pair The sensitivity of Cd and Pb is stronger than that of chlorophyll b.As the concentration of Cd and Pb increases,Fv/Fm,F'v/f'm,?psii and ETR all show a downward trend,indicating that the photosynthetic capacity decreases.(2)Alternanthera philoxeroides has a strong ability to accumulate Cd and Pb.Alternanthera philoxeroides can absorb two heavy metal elements,Cd and Pb,into the body and store them through the roots,and as the concentration of Cd and Pb increases,the absorbed content increases linearly.When the Cd concentration is0.8mmol/L and 2.0mmol/L,the Cd content in leaves,stems and roots are 16.17?g/g,29.62?g/g and 224.47?g/g respectively;when the Pb concentration is 2.0mmol/L,The Pb content in leaves,stems and roots were 163.71?g/g,402.58?g/g and2583.22?g/g,respectively.The content of Cd and Pb in the roots of Alternanthera philoxeroides accounts for more than 75%of the total,indicating that Alternanthera philoxeroides stores two heavy metals in the roots and is difficult to transfer to the leaves and stems.Alternanthera philoxeroides has a strong ability to accumulate Cd and Pb.The maximum BCF for Cd is 4.12,and the maximum BCF for Pb is 8.84.Because the BCF of Alternanthera philoxeroides to Cd and Pb>1,the biomass is huge and the reproduction speed is extremely fast,Alternanthera philoxeroides can be used as a heavy metal hyperaccumulator to participate in the phytoremediation of Cd and Pb.(3)The process of Alternanthera philoxeroides accumulating Cd and Pb triggers changes in the content of active oxygen and changes in the content or activity of antioxidant system substances in the plant.During the process of Cd and Pb enrichment in Alternanthera philoxeroides,excessive Cd and Pb accumulation in Alternanthera philoxeroides caused oxidative stress,and the content of H₂O₂and MDA increased rapidly,showing an increasing trend.With the increase of the concentration of Cd and Pb,the content and activity of each substance in the antioxidant system showed a trend of increasing first and then decreasing.When the concentration of Cd and Pb is low,the content of ROS increases rapidly,causing the content and activity of various substances in the antioxidant system to increase,and the rapid elimination of ROS.When the concentration of Cd and Pb is high,plant life activities are inhibited,the enzyme structure is destroyed,resulting in decreased activity or even inactivation,and the production of non-enzymatic substances also decreases.Therefore,the content of ROS rises rapidly,which inhibits plant growth and even death.