A physic-ecological engineering ( PEEN) for aqua-eco-remedialion was performed in a local area ( enclosed water with surface area of 1.33 ha) with depth round 10 m and variation of water level of 7 m in Lake/Reservoir Hongfeng. Results showed that the construction, abundance and biomass of the phytoplankton may be regulated by PEEN, when the ratio of the Him area of floating islands with plant to the total enclosed area is above 1/5 -1/3 (as the threshold). The dominant phytoplankton populationrnshifted from Cyanophyta (Microcystis), Pyrrophyta (Ceratium hirundineUa) and Cyanophyta (Dactylccoccopsii ackularti) in surrounding algae-type water to Bacillariophyta (Melosira) after the construction of engineering. Species of Cyanophyta in plant-type water were less than that of surroundings at 17.6%-29.4% (especially the species with microcystin, such as Micracystis, Anabae-na, Oscillaloria, Aphanizomenon, were detected in surroundings algae-type water did not been detected in plant-type water); while the species of Bacillariophyta increased to 120.0% in comparison with that in the surroundings. The abundance and biomass of Cyanophyta in the plant-type area of the PEEN decreased by 55.5% and 57.9% in comparison with those in surroundings, respectively. Meanwhile, the abundance and biomass of Bacillariophyta in the plant-type area of the PEEN increased by 56.4% and 60.3% in comparison with those in surroundings, respectively. The total phytnplankton abundance and biomass decreased by 53.6% and 39.1% , respectively in comparison with those of the surroundings. All these facts benefited the increase of transparency in plant-type water, where the water quality improved obviously and the seechi depth is stably observed at 120 - 220 cm and higher than that in surrounding algae-type water in dozen centimeters. The engineering area appears as the " green island" in the algae bloom occupied surroundings frequently. The eutrophication in local area of Lake Hongfeng with surface area of 57.2 km2 at normal water level is controlled without algae bloom. The PEEN including floating eco-islands, which can be used for culturing various water surface plant, including aquatic plant, wetland plant, terrestrial plant ( Vetiver Crass, salix integra linn. , etc), for relieving high wind-driven wave, suppressing blue algae, improving water quality and transparency and other techniques is important for guaranteeing the remediation of submerged vegetation in shallow lakes and preventing algae bloom under severe environmental pressure at present.%利用物理生态工程在水深10m左右,水位变幅7m左右的贵阳红枫湖/水库(正常水位时57.2 km2)右二湾富营养水体进行局部(围隔水体面积1.33 hm2)生态修复.对工程前后和内外水体浮游植物的群落结构、丰度、生物量等进行比较,结果表明,当植物浮岛覆盖率超过1/5 ～ 1/3时(可视为阈值),物理生态工程可以调控浮游植物种群结构和丰度,浮游植物优势种群由生态修复前的微囊藻属、角甲藻属及同期外环境的蓝藻 门蓝纤维藻属转变为硅藻门的直链藻属.工程内与工程外比较,种属数减少了29.4％,特别是减少了蓝藻中可能释放藻毒素的微囊藻、鱼腥藻等属,蓝藻丰度和生物量分别减少了55.5％和57.9％；而硅藻的种属数则增多120.0％,且其丰度和生物量分别增加了 56.4％和60.3％.从藻类总体统计资料看,工程内与工程外比较,藻类丰度减少53.6％,生物量减少39.1％.透明度提高了数十厘米以上,稳定在120～220 cm.当工程区外浮游植物优势种群是蓝藻,暴发蓝藻水华,且可释放藻毒素的种属有多次检出时,工程区内仍然以硅藻为优势种,未曾检测出可释放藻毒素的种属,从而在红枫湖局部水体实现了水质改善和富营养化控制.在目前高污染负荷下恢复浅水湖泊沉水植被时,本项目发展的可全年镶嵌式种植包括香根草、杞柳等高杆植物在内的多种水面植物的浮岛可作为防浪削浪、遏制蓝藻、改善水质、提高透明度的先锋性措施,以保障局部水面植被覆盖面积超过上述阈值,成为保护沉水植物生长、遏制暴发蓝藻水华的可操作途径.
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