Influence Of Elodea Nuttallii-Nitrogen Cycling Bacteria On Nitrogen Cycling Of Shallow Eutrophic Taihu Lake, China

With the rapid development of economy in recent years, water pollution of lake has become serious gradually. In our country, lake eutrophication has become one of serious environmental problems. Lake ecosystem degradation, high frequency of algae bloom occured and water qulity deteriorated in entrophic lake. All these have caused a great threat to drinking water safety. The water column of Taihu lake was mesotrophication, and58.4%water quality was worse than level V in2011.Undisturbed sediment cores were collected from Gonghu Bay and Meiliang Bay, Taihu Lake in the present study. And intergrated Elodea nuttallii-nitrogen cycling bacteria technology was applied as a restoration method. Four groups of restoration incubation were carried out by adding Elodea nuttallii and immobilized nitrogen cycling bacteria (INCB) into the simulation ecosystems. The difference of nitrogen transformations between Gonghu Bay and Meiliang Bay in different ecological restoration measures was investigated. And the influence of Elodea nuttallii-IHCB mutualism system on nitrogen cycling was also discussed. Elodea nuttallii-INCB assemblage was also applied in Gonghu Bay near the drinking water souces to researched water purification effect. The experiment results could be theoretical Basis and technical Support of water restoration. Through the study, the primary conclusions are as follows: (1)After incubations of adding Elodea nuttallii and INCB, the denitrifications of Gonghu Bay and Meiliang Bay were enhanced, and sediment with Elodea nuttallii-INCB assemblage reached the highest denitrification rate among all treatments. Submerged plants roots O2release lead to promote nitrification and then stimulated Dn rates. Besides, added nitrogen cycling bacteria facilitated Dw rates. The comnined effect of Elodea nuttallii-INCB enhanced the total denitrification rates.(2) Among the four treatments, sediment added with INCB showed the higher emission rate of N2O. And the highest N2O fluxes occurred in sediment with Elodea nuttalli-INCB mutualism system applied.(3)The presence of macrophytes enhanced the oxygen penetration depth. O2profiling showed that oxygen penetration in vegetated sediments increased to30mm approximately. But the penetration depths of oxygen in the bare sediment and added INCB sediment were merely10mm.(4) The abundance of nirS, nirK, nosZ genes were dramatically influenced by adding INCB and Elodea nuttallii. Compared to the bare sediment, the copy numbers of nirS, nirK and nosZ genes in sediments with restoration treatments increased. And the abundance of nosZ gene was markedly augmented.(5) The combine effect of Elodea nuttallii and INCB enhanced the denitrification of Elodea nuttallii or nitrogen cycling bacteria. Nitrogen cycling bacteria play a leading role in denitrification and submerged plants would promote the denitrification process.(6) The technology of ecological suspended bed was applied in situ pilot-scale lake restoration test. And this technology had stable effect for water purification:TN concentration reduced40%, NH4+concentration reduced50%, NO3-concentration reduced44%, NO2-concentration reduced49%. The average of N2O flux was12.83μg m-2h-1, which increased obviously after applying the ecological suspended bed. The denitrifying bacteria quantities were found2～3order of magnitude higher than the comparison water. The results indicated Elodea nuttallii-INCB technology can efficiently decrease nutrient loading in water colum and is helpful to improve the water quality.