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我国幅员辽阔,湖泊众多,全国1 km2以上的湖泊有2 759个,总面积达91 019 km2,占国土面积的0.95%[1]。近年来,随着社会发展和人们生活水平的不断提高,城市建设越来越强调生态元素及理念,因此建设了大量的水体景观工程,即人工湖[2]。城市小型湖泊及人工湖能够影响城市微气候,促进物质和能量循环并参与生物修复过程,还具重要的美学和娱乐价值[2-3],以及重要的生态意义[4-5]。然而,这类湖泊通常水域面积较小、水深较浅、流速小、污染源受纳量较高且自净能力有限,容易出现水体富营养化[6-9]。近5年来,我国城市湖泊富营养化日趋严重,浮游藻类大量繁殖会破坏湖泊原有的自然景观,限制城市旅游业的发展,也降低了人民群众的幸福感[5]。
富营养化城市湖泊的治理已成为国内外学者广泛关注的焦点。自20世纪80年代初开始,国内外学者就开展了湖泊生态治理的实践研究。经过近40年的发展,底泥疏浚、人工曝气、水生植物种植等[10-13]生态治理技术得到广泛应用,且均取得了一定成效。但在实际应用中还需要依据每个湖泊的特点,因地制宜地选择相应的某种或者多种生态治理技术对湖泊进行治理。
温州大学明心湖是一个小型人工湖,占地面积约20 000 m2,平均水深0.50 m,因在湖中养有黑天鹅等水禽,又称“天鹅湖”。近年来,明心湖水体富营养化问题日趋严重,湖水透明度低且TN、TP、COD等多项指标高于地表Ⅴ类标准,浮游植物大量繁殖聚集而形成水华。为提升明心湖景观、改善水质,学校于2020年4~5月实施了疏浚、曝气以及水生植物种植等多项生态治理措施。为探究此次生态治理工程的治理效果,本研究分别对工程治理前后的水质及浮游生物群落结构变化进行了为期6个月的连续监测,对明心湖的主要水源温瑞塘河河道进行了同步监测并以此作为对照进行对比分析;在对生态治理工程治理前后明心湖水质及浮游生物群落结构变化的监测分析的基础上,评估生态治理工程对小型富营养化湖泊的治理效果,旨在为此类小型人工湖的日常维护与生态治理治理提供参考样本和数据支持。
富营养化浅水湖泊生态治理措施及效果
——以温州大学明心湖生态治理工程为例Effects of ecological restoration measures on eutrophic shallow lakes
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摘要: 温州大学明心湖长期以来水体透明度偏低且近岸时常出现水华现状,文章于2020年4~5月对该湖实施了底泥疏浚、水生植物种植、曝气等生态治理工程,并通过对治理前后其水质及浮游生物群落结构定期监测。结果表明:治理后5个月,明心湖水体的TN、TP和COD显著下降,分别从3.31、0.17和51.03 mg/L降至0.81、0.05和25.26 mg/L;SD、DO和pH平均值显著升高,分别由0.14 m、7.06 mg/L、7.28升至0.31 m、10.53 mg/L和8.10;浮游生物的丰度均显著下降,浮游植物中绿藻的相对丰度显著上升,而浮游动物中枝角类和轮虫类的相对丰度显著下降。综上,生态治理工程实施后,明心水体透明度显著提高,营养盐水平、叶绿素a浓度及浮游生物丰度显著下降。Abstract: Mingxin Lake, a small, eutrophic and shallow lake located in the campus of Wenzhou University, has a long history of low transparency and frequent occurrence of algal blooms near the shore. To improve the situation, the ecological restoration projects including dredging, cultivation of aquatic plants and aeration were performed in the Mingxin Lake from April to May in 2020, and the effects of these ecological restoration projects were evaluated by the regular monitoring of the water quality and the plankton community of the Mingxin Lake before and after the treatment. The results showed that levels of TN, TP and COD in the Mingxin Lake significantly reduced after the implementation of the ecological restoration projects. In 5 months, the average concentration of TN, TP and COD in the Mingxin Lake decreased to 0.81, 0.05 and 25.26 mg/L from 3.31, 0.17 and 51.03 mg/L, respectively. On the other hand, the SD, DO and pH of waters increased significantly. The average SD increased from 0.14 m to 0.31 m in 5 months, the average concentration of DO increased from 7.06 mg/L to 10.53 mg/L, and the average pH value increased from 7.28 to 8.10. After implementation of the ecological restoration projects, the plankton abundance in the Mingxin Lake decreased significantly. The relative abundance of green algae in total phytoplankton increased significantly, while the relative abundance of cladocerans and rotifers in total zooplankton decreased significantly. In conclusion, the water quality in the Mingxin Lake improved significantly after the implementation of the ecological restoration projects, the transparency significantly improved, the nutrient level and the chlorophyll a concentration as well as the plankton abundance significantly decreased.
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表 2 治理前后明心湖和温瑞塘河浮游动物优势种及其优势度的变化
门类 优势种 治理前 治理后 明心湖 温瑞塘河 明心湖 温瑞塘河 轮虫 矩形龟甲轮 Keratella quadrata 0.05 0.06 0.04 0.20 针簇多肢轮 Polyarthra trigla 0.12 0.20 0.13 0.05 壶状臂尾轮 Brachionus urceus 0.20 - 0.02 0.03 晶囊轮 Asplanchna 0.06 0.08 0.06 0.11 真翅多肢 Polyarthra euryptera - 0.08 0.03 0.06 截头皱甲轮 Ploesoma truncatum - 0.04 0.02 0.11 长三肢轮 Filinia longiseta - - 0.04 0.05 脾状四肢轮 Tetramastix opoliensis - - 0.11 0.04 圆筒异尾轮 Trichcerca cylindrica - - 0.05 - 萼花臂尾轮 Brachionus calyciflorus 0.02 0.04 0.03 0.11 独角聚花轮 Conochilus unicornis - - - 0.06 枝角类 长肢秀体 Diaphanosoma leuchtenbergianum 0.08 0.07 0.03 0.04 微型裸腹 Moina micrura - 0.04 0.17 - 多刺裸腹 Moina macrocopa 0.03 0.03 0.04 0.03 长额象鼻 Bosmina longirostris 0.02 0.09 0.06 0.08 平突船卵 Scapholeberis kingi 0.21 - - - 桡足类 近邻剑水 Cyclops vicinus 0.02 0.03 0.03 0.03 广布中剑水 Mesocyclops leuckarti 0.02 0.06 0.03 0.06 注:“-”表示优势度未达到0.02。 表 1 治理前后明心湖和温瑞塘河浮游植物优势种及其优势度的变化
门类 优势种 治理前 治理后 明心湖 温瑞塘河 明心湖 温瑞塘河 硅藻门 脆杆 Fragilaria sp. 0.04 0.07 0.02 0.09 针杆 Synedra sp. 0.03 0.06 0.02 0.04 桥弯 Cyclotella sp. 0.02 0.03 - - 异极 Gomphonema sp. 0.03 0.02 0.02 - 变异直链 Aulacoseira varians 0.04 0.06 0.03 0.03 小环 Cyclotella sp. 0.04 0.06 0.04 0.03 舟形 Navicula sp. 0.04 - - 0.02 颗粒直链 Aulacoseira granulate 0.09 0.09 0.09 0.09 绿藻门 衣 Chlamydomonas sp. 0.02 0.04 0.03 0.03 空球 Eudorina sp. 0.03 - 0.09 - 弓形 Schroederia sp. 0.02 - 0.02 - 小球 Chlorella sp. - 0.03 0.02 0.02 针形纤维 Ankistrodesmus acicularis 0.03 0.03 0.02 - 单角盘星 Pediastrum simplex 0.06 - 0.09 0.05 二形栅 Scenedesmusdimorphus 0.02 0.04 0.02 - 二尾栅 Scenedesmus bicauda 0.02 0.03 - - 四尾栅 Scenedesmus quadricauda 0.04 0.05 0.03 0.03 四足十字 Crucigenia tetrapedia 0.03 - - - 新月 Closterium sp. 0.03 0.03 0.02 - 纺锤 Elakatothrix sp. - - - 0.02 鼓 Cosmarium sp. 0.04 0.03 0.02 0.02 隐藻门 隐 Cryptomonas sp. 0.05 0.05 0.03 - 裸藻门 裸 Euglena sp. - 0.07 - 0.03 梭形裸 Euglena acus - 0.06 - 0.08 裸囊 Trachelomonas sp. 0.02 0.04 - 0.04 蓝藻门 隐球 Aphanocapsa sp. - 0.05 - 0.04 注:“-”表示优势度未达到0.02。 -
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