| 摘要: |
| 五里湖是太湖西北部一个小型浅水湖湾,是无锡市的饮用水源和主要风景游览区。50年代时,该湖基本保持着原始状态,全湖以大型水生植物占优势。湖水清澈见底,水质为中营养水平,溶氧接近饱和,对外来的N、P污染冲击具有很强的缓冲能力。底泥的氧化程度较高,磷和有机物含量仅为0.023%和0.75%。浮游藻类受到了大型水生植物的强烈抑制,年均数量为26.7×104个/L,以硅藻和隐藻为主;从春季至秋季,随着大型水生植物的增长,浮游藻类数量大幅度减少。浮游动物多达190种,年均数量为5660ind./L。大型底栖动物较多,以日本沼虾和螺、蚌类为主。鱼类资源十分丰富,63种鱼中以凶猛性鱼类占优势,并有较多的底栖性鱼类。自50年代以来,大约有1/2的湖面被围垦,沿岸带生态条件被破坏,失去了最适合于大型水生植物生长的浅水区。加之60年代后期在全湖放养草鱼,水生植被遭到彻底毁灭。外源污染加剧,引起了水质的严重富营养化。围垦和修建水闸隔断了五里湖与太湖间的通道,限制了两个水体间的水流交换,妨碍了污染物的稀释扩散,使得来自无锡市区的污水成了五里湖的主要补给水源,加速了富营养化的进程。五里湖水质已达重富营养水平,透明度小于0.5m,缺氧较为严重。营养物在底泥中大量积累,TP和TOC含量分别增高了4.17倍和1.87倍。在春末夏初,由于底泥中污染物的释放而引起水质严重污染。浮游藻类大量繁殖,年均数量达4174×104个/L,是1951年的156倍,蓝藻水华极为严重。浮游动物数量明显减少,年均数量902ind./L,仅是1951年的16%。大型底栖动物基本消失,耐污的水丝蚓和摇蚊幼虫占据优势。凶猛性鱼类几乎绝迹,全湖只放养链、鳙鱼,密度约为600-750kg/hm2。五里湖富营养化治理势在必行。我们虽不能完全恢复五里湖的全貌,但可以对现有的湖面进行彻底的污染治理和生态恢复。重建水生植被是实现其生态恢复的重要途径,但较深的湖水和低的透明度成了限制水生高等植物生存的主要环境因子,改善这种环境条件将成为重建水生植被的关键。五里湖是众多浅水富营养湖泊的典型代表,污染、放养草鱼、围垦、水利控制、修建人工湖岸等多重人为干扰是导致这些湖泊富营养化的共同根源,因而具有相似的生物和环境特征,研究五里湖富营养化及其治理途径对其它同类湖泊具有广泛的指导意义。 |
| 关键词: 五里湖 富营养化 环境演变 |
| DOI：10.18307/1996.sup06 |
| 分类号: |
| 基金项目: |
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| Biological and environmental succession in wuli bay of taihu lake along with the eutrophication processes |
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Li Wenchao
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Nanjing Institute of Geography & Limnology, Chinese Academy of Sciences, Nanjing 210008
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| Abstract: |
| Wuli Bay, a small and shallow bay of Taihu Lake in the northwestern comer, is a drinking water source and famous scenic spot. In the 1950's, Wuli Bay still remained its original beauty. It was covered by aquatic macrophyte and the lake water was clear enough to see the bottom. The water was in mesotrophic level and nearly saturate with oxygen. The system had very strong buffering capacity to nitrogen and phosphorous pollution. The sediment was well-oxidized and had low content of TP(0.023%) and TOC(0.75%). Phytoplankton was intensely suppressed by aquatic macrophyte to an annual mean density of 26.7×104 ind./L with diatom dominated. More than 190 species of zooplankton was found with a mean density of 5 660 ind./L. Abundant large benthic animals was dominated by Macrobrachium nipponens, Stenothyra glaloroa and Corbicula fluminea in the bay. It was rich in fishery resource and piscivorous fish took the dominance. Since 1950, about half of the lake surface has been diked and the littoral zone environment, the best living habitat for aquatic macrophyte, has been destroyed. In the late 1960's, grass carp was introduced to Wuli Bay which led to the disappearance of macrophyte, and eutrophication occurred with increasing pollution. The dike-dam and sluice broke the connection between Wuli Bay and Taihu Lake. So, the waste water from Wuxi City became the main inflow of Wuli Bay and eutrophication was enhanced. The lake water in Wuli Bay is now in hy-pereutrophic level with low secchi depth(<0.5m) and serious oxygen shortage. TP and TOC has accumulated in the sediment to 5.17 and 2.87 times as high as in 1951, and heavy "bot-tom-up" effect was found in the late spring of 1993 and 1994. Algal-bloom occurred over the year with a mean density of 4 174*104 ind./L, which was 156 times as high as in 1951. Zooplankton decreased to 902 ind./L(16% of that in 1951) and very few large benthic animals found alive. The whole bay was used as a fish pond for silver carp and big head, pisciverous fish disappeared from the bay. Wuli Bay is still the important drinking water source and scenic spot of Wuxi City although the water is eutrophic and the environment is terrible. We could not return Wuli Bay to its original condition, but it is possible to control the pollution and restore the present lake area to clear water and mesotrophic state. It is an efficient way to restore the Wuli Bay by recovering aquatic vegetation, but the deep water and low transparency made it difficult for the macrophyte to live. It is very important to improve water transparency before recovering vegetation. Wuli Bay is a typical sample of shallow eutrophic lakes, and the achievements in research on eutrophication and restoration of Wuli Bay could be used to other similar lakes. |
| Key words: Wuli Bay eutrophication environmental succession |
