Study On The Remediation Of Heavy Metals Polluted River Sediment At Shallow Area By Submerged Plants Incold Zone

In this study, the Surface sediment, from Songhua River of Harbin section near Sun Island was selected as the main research object. We used the researching model simulating river conditions, controlled the water temperature at 22℃±2℃,to explore the enrichment effects of Vallisneria natans and Elodea nuttallii for Cd, Zn and Pb in sediment,as well as the changes in rhizosphere sediment environment before and after the restoration of submerged plants, respectively under high flow rate of 0.022 m/s, low flow rate of 0.011cm/s, strong light of 60mol/(m2·s) and weak light of 30mol/(m2·s)conditions. The purpose of the study is to provide some scientific references for the feasibility and screening predominant plant species for using Submerged Macrophytes to restore the heavy metals polluted sediment in shallow area of Songhua River of Harbin section and other cold zone.The heavy metals polluted sediments have repaired 60 days by Vallisneria natans and Elodea nuttallii.,the results show that:(1) Both Vallisneria natans and Elodea nuttallii can grow healthily, and there are no obvious heavy metal stresses. All of them have accumulation capacity of Cd, Zn and Pb in polluted sediment, and the average enrichment amount sequence of each period was Zn > Pb > Cd.(2) The two kinds of Submerged Macrophytes basically show rising trends of the average enrichment amount for Cd and Zn. The accumulation of Vallisneria natans and Elodea nuttallii for Pb both increase gradually in the weak light, but all increase first and then decrease, in high and low velocity conditions, and the maximum of them reach respectively at 45 days and 30 days.(3) The average enrichment amount of Vallisneria natans and Elodea nuttallii for Cd, Pb and Zn in each period are basically manifested: high velocity group are higher than low velocity group, strong light group are higher than weak light group.(4) Under the same light intensity, The average enrichment amount of Vallisneria natans for Cd and Zn are both higher than those of Elodea nuttallii. But In high velocity condtion, Vallisneria natans’ s average enrichment amount for Cd, Pb and Zn are all lower than those of Elodea nuttallii.(5) The laws of BCF, in all Conditions conducted in this study, are basically the same as those average enrichment amount regularities of Vallisneria natans and Elodea nuttallii for Cd, Pb and Zn.(6) Correlation and regression analysis show that there are good linear negative correlations for the contents of Cd, Pb and Zn between Submerged Macrophytes and rhizosphere sediments. In other words, the contents of Cd, Pb and Zn in rhizosphere sediments have been reduced in their own ways, as them were continuously enriched by Vallisneria natans and Elodea nuttallii.The rhizosphere sediment environments have changed obviously after restoration by Vallisneria natans and Elodea nuttallii under different conditions:(1)The basal respiration rates of rhizosphere sediment are significantly higher than those of original sediment and non-rhizosphere sediment, which means phytoremediation has enhanced the quantity and activity of microorganisms in rhizosphere sediment.(2) The contents of Organic Matters(OM) in rhizosphere sediments restored by Submerged Macrophytes, excluding the high velocity group of Elodea nuttallii, have been decreased compared with original sediment.(3)After repairation, the contents of TP(Total phosphorus), IP(Inorganic phosphorus), OP(Organic phosphorus) and NAIP(Non-apatite inorganic phosphorus) in the rhizosphere sediment have been decreased differently, but the amount of AP(Apatite phosphorus)is not changed. The reduction of TP is mainly caused by IP reduction, which is mostly caused by NAIP, and OP reduction also has a greater contribution. The sequences of TP, IP and NAIP decrease among different groups of Vallisneria natans and Elodea nuttallii are low flow rate group > high flow rate group, strong light group > weak light group,which is the same as those of OP among Vallisneria spiralis groups. The differences of OP among Elodea nuttallii groups are not significant. In the same condition, reductions of TP, IP, NAIP and OP in Vallisneria natans groups are all greater than those in Elodea nuttallii groups.(4) After restoration, accumulation index evaluation shows that the pollution levels R of Cd in sediments of all groups have been reduced to 5, although the pollution levels of Pb and Zn were not changed, but their Igeos have been decreased differently.