The Restoration Effect Of Common Submerged Macrophytes On Cd, Cu, Pb, Zn, In Sediments Of Aqutic System

Heavy metal pollution in water is the process that heavy metals are discharged into water body exceed the self-purification capacity of water, resulting in a change in the composition and properties of water body. In this case, the waters biological growth conditions deteriorate, and human life and health has been adversely affected. Heavy metals are diffuclt to dissolve into the water. When the heavy metals are discharged into water body, majorities of heavy metals change quickly into solid phase from water phase and eventually deposite into the sediment in the water. The main sources of heavy metal pollution are industrial-agricultural waste and domestic waste. Sediment is an important part of many aquatic ecosystems, such as rivers and lakes, and it plays an important role in the aquatic environment. If the environment changes, the heavy metals in the sediment will release into the water again and cause secondary pollution. so it is badly needed for us to carry out the research on restoration technology of the heavy metal polluted water environment.Aiming at the problems of heavy metal pollution in the sediments of water bodies, We try to purify water quality by using four common submerged macrophytes for the enrichment of cadmium, copper, lead, zinc in contaminated sediment in simulated conditions. In this study, we carried out two aspects of the work. The fist one was carried in winter and spring. Potamogeton crispus, which flourishes in winter and spring, was used to accumulate the cadmium, copper, lead, zinc in contaminated sediment in simulated conditions in three different planting densities. The density gradient are30plants/aquarium,45plants/aquarium,60plants/aquarium, respectively. The enrichment and biota-sediment accumulation factor (BSAF) are calculated to know the effects of accumulating cadmium, copper, lead, zinc. And then the better planting density for enrichment of various heavy metal. is filtered out. At the same time we monitored the dynamics of the plants absorbing heavy metals process in order to discover the law of plant accumulating heavy metals. The second part was conducted in spring and summer. Three common submerged macrophytes are choosed as the experimental material. The plants are Vallisneria natans, Hydrilla verticillata and Ceratophyllum demersum. The heavy metal enrichment experiment was performed in the same planting density in the analog staticly simulated water. The enrichment amount and biota-sediment accumulation factor (BSAF) are also calculated to find out the effects of the plants accumulating cadmium,copper, lead, zinc. We try to select the better species for concentration of various heavy metal.The results of our study as follow:1. The enrichment effects of Potamogeton crispus on the same heavy metal are different in different planting densities. The Cd enrichment effect sequence is45plants/aquarium group>60plants/aquarium group>30plants/aquarium group. The Cu enrichment effect sequence is45plants/aquarium group>30plants/aquarium group>60plants/aquarium group. The Pb enrichment effect sequence is45plants/aquarium group>60plants/aquarium group>30plants/aquarium group. The Zn enrichment effect sequence is30plants/aquarium group>45plants/aquarium group>60plants/aquarium group. According to our experimental results, we speculate that45plants/aquarium is the best planting density for Potamogeton crispus accumulating Cd, Cu, Pb. And30plants/aquarium is the best planting density for Zn.2. Potamogeton crispus showed significant enrichment for Cd, Cu, Pb, Zn in sediment. Potamogeton crispus have different enrichment amount and BSAF in different planting densities. The four heavy metals enrichment ability sequence in the30plants/aquarium is Zn> Cu> Pb> Cd. The four heavy metals enrichment ability sequence in the45plants/aquarium is Zn> Cd> Cu> Pb. The four heavy metals enrichment ability sequence in the60plants/aquarium is Zn> Pb> Cu> Cd. It suggested that planting density can affect the absorption of havy metals. As for Potamogeton crispus, the Zn enrichment ability is the strongest in whatever density of the three.3. Compared biomass, enrichment amount and BSAF between these three submerged macrophytes in the same experiment condition, it was knew that the breeding capacity sequence of three plants is Vallisneria natans>Hydrilla verticillata> Ceratophyllum demersum. For Vallisneria natans, the enrichment amount sequence is Zn> Pb> Cu> Cd, and the enrichment ability sequence is Cd> Zn> Pb> Cu. For Hydrilla verticillata, the enrichment amount sequence is Cu> Pb> Zn> Cd, and the enrichment ability sequence is Cu> Cd> Zn> Pb. For Ceratophyllum demersum, the enrichment amount sequence is Pb> Cu> Zn> Cd, and the enrichment ability sequence is Cd=Cu> Zn> Pb.4. All the three submerged plants have strong bioaccumulation capacity of Cd, Cu, Pb, Zn. The biota-sediment accumulation factor is greater than1. The one submerged plant has different enrichment characteristics for accumulating Cd, Cu, Pb. Zn.5. The three submerged plants have different accumulation ability for the same element. The Cd, Pb, Zn enrichment ability sequence is Vallisneria natans>Hydrilla verticillata> Ceratophyllum demersum. But the Cu enrichment ability sequence is Hydrilla verticillata> Ceratophyllum demersum> Vallisneria natans. Vallisneria natans can be a pioneer plant for ecological restoration of Cd, Pb, Zn composited pollution sediments. Hydrilla verticillata can be used as a species of copper single pollution in ecological restoration.6. There are a significant negative correlation (p<0.01) beween the heavy metals of the submerged macrophytes and sediments.Curve estimated by regression analysis, we can see that the heavy metal content (y) in the submerged macrophytes and sediment heavy metal content (x) is a linear regression relationship. The general formula of the regression equation is y=-ax+b. The determination coefficient R2is close to1, and the regression model have reached a very significant level (p<0.01).