Approaches to the Ecological Recovery Engineering in Lake Shishahai, Beijing

什刹海是北京市一个小型浅水城市风景游览的富营养湖泊.生态恢复试验工程以物理除藻为前提,通过实施基底修复而后开展水体充氧等手段,达到恢复水生植被的根本目的.应用的修复技术有:(1)臭氧/超声波除藻;(2)基底修复;(3)水下曝气充氧及冬季冰下底部充氧;(4)上游区复合生物浮床;(5)水下光补偿技术;(6)高等水生植物栽植与优化配置;(7)水生植物调控与机械割草;(8)水质净化与保洁管理.工程实施近1年(2001年8月-2002年6月)后效果明显,总氮、总磷分别下降了4.74mg/L和0.45mg/L,去除率达到79%和91%,什刹海的水质也由Ⅴ类上升为Ⅳ类.;Shishahai Lake is a scenic and sightseeing lake in central Beijing.Before the ecologic recovery testing, it was under heavy eutrophication.Indexes of B0D5;NH3-N, Permanganate Index and TP were over Y-Class of Chinese Environmental Quality Standards For Surface Water with dominant alga of bellamya microcystis.Several technologies were used in the ecological recovery for Lake Shishahai, i.e., ozone/supersonic algae removal, aeration, floating bio-bed technology, lake bottom recovery, hydrophyte planting and recovering and biological adjustment and control.After more than ten months' testing of ecological recovery, the ecological environment has improved obviously.TN and TP content are 1.26mg/L and 0.046mg/L, which were reduced 79% and 91% separately for TN and TP.Meanwhile, the chlorophyll.a content was decreased with notable deeper transparency in the lake.The general evaluation of water quality is IY Class.