Study On Bioremediation Using Eichhornia Crassipes As Dominant Aquatic Macrophyte In Copper Polluted And Eutrophic Water

In the last 30 years, with economy and living conditions fastly developing,abaundant nutrient and organic pollutants were poured into water bodies such as river,lake and reservoir with effluent discharge. Large area aquatic ecological systems aredegraded, and especially the problem of water eutrophication becomes increasinglysevere. Copper and other potential toxic metals are often contained in some waste water,and copper salt is also usually used to control algae and improve water quality in themanagement process of eutrophic water. Under high concentration exposure of copper,aquatic organism may be damaged to death and copper may come into food chain, andsafety and health of human and animal also may be impacted seriously by copper throughfood web. In present, aquatic macrophytes have attracted extensive attention around theglobe in bioremediation of heavy metal-polluted and eutrophic water. To provide sciencetenability for bioremediation of copper contamination and its toxicity, copperaccumulation and the adaptation of Eichhornia crassipes to copper stress wereinvestigated in this study. Further study was carried out for copper-removal of acopper-resistant strain isolated from the root of E. crassipes, and improving effect of theisolated strain in detoxification of Potamogeton crispus to excessive copper. For theeutrophication of Yanghe Reservoir in Hebei Province of China, the polluting process andcurrent situation of nitrogen and phosphorus in the reservoir and its upper reaches of WestYanghe were analysed. By simulating the open water area of the reservoir, ecologicalenclosers of single aquatic plant and combination ecological system consisted of differentlife-form plants were studied to explored the application of E. crassipes,and other aquaticplants in improving eutrophic water quality of Yanghe Reservoir.Under moderate concentration of copper (0.5-5 mg/L of Cu²⁺), E. crassipes hadstrong copper-accumulated ability, and the plant also could detoxificate copper stress tosome extend. The average copper content in different tissues of E. crassipes was as highas 314 mg kg^-1 dry weight (14 d). The accumulated copper was mainly distributed in theroot, and the highest copper content in the root was more than 1800 mg kg^-1 dry weight (8d). When exposed to moderate concentration of copper, three pigment concentration in leaf of the plant showed a down-up regulation, which due to the protection of threeantioxidase including SOD, POD and CAT defensing from lipid peroxidation damageinduced by copper toxicity. For exposure to high concentration of copper, although somestress parameters such as pigment concentration and lipid peroxidation product wereimpacted seriously, the plant showed high potential capability of copper accumulation,which was demonstrated by that the average copper content in the plant reached 300 mgkg^-1 dry weight at least, but the plant died at 6 d. The appearance of the root haddegenerated under the stress induced by copper accumulation, while the plant could stillremain growing at a longer time (30 d). When observed under contrast microscope, therewere many bacteria in the rhizosphere of E. crassipes. It was indicated that some of theserhizospheric bacteria played an important role in detoxification of the root to excessivecopper.Further study demonstrated that a copper-resistant strain, ACU, isolated from theroot of E. crassipes had strong copper-tolerant ability and copper-removal capability.ACU is a new species of bacteria in the family of Enterobacteriaceae, which suggestedby the detection of its 16S rDNA sequence (GenBank EF 151985). Result of SDS-PAGEanalysis showed that the copper-removal mechanism of ACU may be dued to secretprotein, through which copper was binded to become complex or precipitation. Byinoculation with ACU on the surface of P. crispus, the increase rate of the plant biomasssignificantly showed ascending trend, when exposed to low or moderate concentration ofcopper. Even for exposure of high concentration of copper, the lethal time of the plantcaused by copper toxicity was delayed from 4 d to 8 d in ACU inoculation treatment.When observed by contrast microscope, the structures of the root and the leaf of P.crispus treated with inoculation of ACU were relative integrity in moderate concentrationof copper stress. These findings indicated that ACU played a significant role indetoxicfication of P. crispus to stress of excessive copper, and even accelerated growthand development of the plant to some extend.When tested by artificial ecological encloser, all tested aquatic plants grew well andimproved water quality and transformed the trophic state of the reservoir, and so did theircommunities combined with several aquatic plants such as E. crassipes and P. crispus. Results of artifical enclosers experiment showed that all tested aquatic plants decreasedthe nutrient level of nitrogen and phosphorus in eutrophic water of the reservoir,moderated organic pollutant load, and also improved dissolved oxygen concentration.During 50 d of monitoring period, water trophic state of all tested enclosers except thecontrol was transformed from eutrophic state to moderate trophic state. On this base, E.crassipes and other aquatic plants with inlay combination and combination in series wereused to remediate the eutrophic water of Yanghe Reservoir by stepwise method under thesimulation of open and flowing condition. By construction of artificial complexecosystem (ACE), the inlay combination of E. crassipes and other aquatic plants pulssingall combination in series showed efficiant removing ability for nitrogen and phosphorus,and the inlay combination of E. crassipes, Trapa manshurica and Nymphaea tetragonashowed better removal efficiency for redox organic pollutants than the inlay combinationadding other combination in series. The trophic state of water in the engineering was alsotransformed from primary eutrophic level to moderate trophic level after treatement withACE.As showed above, E. crassipes had important application value in bioremediation ofmoderate copper-polluted water, and its rhizospheric copper-resistant strain ACU had alsoa promising application in copper-removal and detoxification of P. crispus to copperstress. Additionally, E. crassipes and other aquatic plants could play an active role inecological remediation of eutrophic water in Yanghe Reservoir.