东太湖水生植物群落结构的演变及其沼泽化

Evolution of community structure of aquatic macrophytes in East Taihu Lake and its wetlands

2002年东太湖水生植被调查结果表明,沉水植被和浮叶植被是该湖水生植被的主要生态类型,分布面积分别占全湖总面积73.6%和18.3%。东太湖水生植被主要有9个群丛,其中沉水植被主要的5个群丛是伊乐藻(外来种)群丛、金鱼藻群丛、伊乐藻+微齿眼子菜群丛、菜-伊乐藻+微齿眼子菜群丛、苦草+竹叶眼子菜+黑藻群丛,其分布面积分别占东太湖植被总面积的30.7%、17.2%、16.7%、15.8%、9.3%。随着对东太湖的不断改造和资源的不断利用,20世纪60年代东太湖人工种植沼泽植被菰群丛,20世纪80年代初环湖水陆交错带被围垦而芦苇群丛消失,微齿眼子菜替代竹叶眼子菜而占据东太湖40%的水面。近10a来,东太湖网围养蟹迅速发展,占全湖总植被面积25.6%的沼泽植物——菰群丛及其占40%的微齿眼子菜群丛被清除,外来种伊乐藻和无根植物金鱼藻分布面积达90%的湖区。东太湖水生植被由20世纪50年代的原生演替到现在的次生演替,群落演变激烈,同时东太湖沼泽化进程加剧。

Two groups of aquatic plants dominated in East Taihu Lake during the field survey in 2002. The submersed macrophytes covered 73.6% of the lake surface, while the floating-leaved macrophytes covered 18.3%, respectively. After detailed classification, five mainly macrophyte asssemblages such as Elodea nuttalli （non-native species） association （30. 7 % of the total vegetation area of the waterbody）, Ceratophyllum demersum association （17.2%）, Elodea nuttalli-Potamogeton macckianus association （16.7%）, Nyrnphoides peltata-Elodea nuttalli-Potarnogeton rnacckianus association （15.8%） andVallisneria spiralis-Potamogeton malaianus-Hydrilla verticillata association （9.3%） were set up to describe the macrophytes community structure in the lake. Previous studies showed that significant changes in the macrophyte community structure started in the 1960s after the introduction of Zizania caduciflora; Phragrnites australis in the littoral zone disappeared at the beginning of the 1980s; Potarnogeton malaianus was replaced by Potarnogeton rnacckianus, which then occupied 40% of the water area, and became the dominant species of submersed macrophytes in the lake. In the past 10 years, enclosure aquaculture of crabs developed rapidly in East Taihu Lake. As a result, the marsh plant Zizania caduciflora （which was covering 25.6% before） and Potarnogeton rnacckianus （which was covering 41% before） disappeared. They were replaced by the introduced species Elodea nuttalli and the rootless plant Ceratophyllurn dernersurn, which covered over 90% of the lake in 2002. The macrophyte communities in the lake have changed markedly since the primary succession status in the 1950s towards the secondary succession status observed in this study. Despite the substantial economic benefits from the crab culture, the aquatic environment in East Taihu Lake is getting worse, especially resulting in water pollution and the acceleration of its swampiness.