Ecological Restoration Of Eutrophic Water By Daphnia Magna And Aquatic Plants

According to the characteristics of eutrophication water in China,the establishment of a rapid and effective ecological restoration system can greatly improve the efficiency of eutrophic ecological restoration.The study combined with Biomanipulation technology and Phytore mediation technology to study the combined restoration effects of Daphnia magna,phytoplankton(Scenedesmus Obliquus)and hydrophyte combination(Thalia dealbata.-Alisma plantago-aquaticaLinn.-CyperusalternifoliusL.)on eutrophic water respectively,in order to provide theoretical basis for the restoration of eutrophic water.The main conclusions are as follows:(1)In the experiment on the purification of eutrophicated water by Daphnia-Algae system,the addition of Daphnia magna could significantly control the growth of Scenedesmus Obliquus.The concentrations of COD and BOD in Daphnia-Algae system water were lower than those in control group without Daphnia.Daphnia magna can reduce the organic pollutants in water by grazing on Scenedesmus 0bliquus.(2)In the experiment on the purification of eutrophicated water by hydrophyte system,all kinds of hydrophytes grew well.The average growth rate of height and the longest root length of the three emerged plants from high to low were Alisma plantago-aquaticaLinn.>Thalia dealbata>CyperusalternifoliusL.Alisma plantago-aquaticaLinn average growth rate of height and the longest root length were 27.45%and 73.67%.Thalia dealbata growth rates of two indexes were 20.82%and 48.97%.CyperusalternifoliusL.growth rates of the two indexes were 19.30%and 24.29%.The removal rates of TN,TP and COD in the hydrophyte system composed of Thalia dealbata-Alisma-plantago-aquaticaLinn.-CyperusalternifoliusL.were76.02%,59.58%and 60.87%.The system can remove TN,TP and COD in water.(3)In the experiment on the purification of eutrophicated water by Daphnia-Algae-hydrophyte system showed that all kinds of plants could still grow well under the initial algae density of 5×10~5cell/mL.The average growth rate of height and the longest root length from high to low were Alisma plantago-aquaticaLinn.>Thalia dealbata>CyperusalternifoliusL.The growth of these two indicators indicators follows:Alisma plantago-aquaticaLinn.increased by 10.34%and 9.38%;Thalia dealbata rose by 5.53%and 7.40%;CyperusalternifoliusL.rose by 5.13%and 4.32%.In the Algae-Hydrophyte co-culture group.The growth rates of the two indexes of Alismaplantago-aquaticaLinn.Were 6.32%and 5.88%;The growth rates of the two indexes of Thalia dealbata were 5.56%and 8.23%;The growth rates of the two indexes of CyperusalternifoliusL.were 5.05%and4.26%.The average growth rate of plant height from high to low was Alisma plantago-aquaticaLinn.>Thaliadealbata>CyperusalternifoliusL.;The average growth rate of the longest root length from high to low was Thalia dealbata>Alisma plantago-aquaticaLinn.>CyperusalternifoliusL.The average height of Alisma plantago-aquaticaLinn.and Thaliadealbata in Daphnia magna group increased significantly,which indicated that Daphnia magna had a positive effect on plant growth.(4)In the experiment on the purification of eutrophicated water by Daphnia-Algae-hydrophyte system showed that the removal rates of TN,TP and COD in water were47.69%,47.59%and 71.93%respectively.The addition of Daphnia magna can maintain the pH value at the optimum level,which is beneficial to the purification.(5)In the experiment on the purification of eutrophicated water by hydrophyte system and Daphnia-Algae-hydrophyte system,the turbidity and odor of the water were found before the experiment.After the experiment,the transparency of the water body increased significantly and the odor of water disappeared.The results showed that the combination of Daphnia magna and hydrophyte had strong purification efficiency for eutrophic water.(6)In the closed water environment,Daphnia magna releases nutrients during its metabolic activities.Therefore,it should be salvaged in time and can be used as bait for aquatic fishes to realize win-win benefits and economic benefits.