Influence Of Macrophytes-Immobilized Nitrogen Cycling Bacteria Assemblage As A Ecological Restoration Measure On Denitrification Rate In The Sediment Of Gonghu Bay, Taihu Lake And In Situ Applied Purification Study

With the rapid development of our country’s economy, a great amount of N load was discharged into nature water column, caused serious lake eutrophicarion. The total water level of Taihu Lake was worse than V, and the water column was mild eutrophicated in2010. As the common water source shared by Wuxi and Suzhou city, Gonghu was constently suffered by the excessive N input in recent years. The water quality deteriorated, blooms of algae frequently occurred and large area of macrophyte meadows vanished in Gonghu Bay. All these has caused a great threat to drinking water safety.Bare zone without macrophytes of Gonghu Bay in northen Taihu Lake was chose as sampling site for the present study. Sediment cores were sampled and four groups of restoration incubation were carried out by accurately adding Elodea nuttallii and immobilized nitrogen cycling bacteria (INCB) into the microcosms. The influence of macrophyte-INCB assemblage on sediment denitrification rates and mechanisim of sediment-water interface (SWI) N cycling were also investigated by appling isotope pairing technique (IPT). Elodea nuttallii-INCB assemblage as a in situ restoration method, was also applied in the lake water column in autumn and winter. The rejointed effect of water purification was significant and it supplied a feasible choise for eutrophic lake restoration. Main conclusions are summarized as follows:(1) Denitrification of sediment with Elodea nuttallii-INCB assemblage reached the highest rate among all treatments. The effects of plant roots O2exertion and benthic nitrogen cycling bacteria enrichment caused great influence on sediment O2penetration and porewater inorganic nitrogen characteristics and contents. The increase of oxic-anoxic interface lead to a stimulation of total denitrification. Due to different nitrate sources be used during coupled and uncoupled denitrification processes, Dn was mainly enhanced by deeper O2penetration in the rhizosphere of vegetated sediment, while the Dw was mainly influenced by the increased nitrate concentration in SWI and porewater.(2) According to the measurement of dissolved O2microoptode in sediment, the02exertion of macrophytes led to a deeper O2penetration and an altemess of aedox conditions in rhizosphere. Compared to the bare sediment, the O2penetration depth was increased from4mm to20mm in vegetated sediment. While the richment of nitrogen cycling bacteria in the upper layer showed no significant influence to the sediment O2profile.(3) Denitrifier in upper layer of sediment was effectively enriched through INCB diffusing. The quantity of denitrifier in E-INCB sediments (within-2cm) showed a significant increasing trend from18×105to350×105cells/g wet weight (ww). Increased quantity of denitrifying bacteria was one of the key factors enhancing the sediment N cycling, especially the denitrification process.(4) According to the5-month long in situ river purifying experiment, the TN concentration reduced6%～61%, NO3-concentration reduced6%～68%and COD concentration reduced4%-78%. The result showed nitrogen bacteria quantities increased markedly after releasing INCB, and the MPN values of denitrifying bacteria in the enclosure was3-4order of magnitudes higher than the comparison water. Furthermore,9-month long in situ pilot-scale lake restoration test showed that the TN concentration reduced39%, NH4+concentration reduced46%, NO3-concentration reduced52%, NO2-concentration reduced57%and COD concentration reduced45%in average respectively.Two in situ water purification experiments showed Elodea nuttallii-INCB assemblage technique can efficiently decrease nutrient loading in water coloum and is helpful to lake water source eutrophication control.