近2000年来杭州西湖藻类种群的演替与富营养化的发展过程

Algae Species Succession and Trophic Developing Process During the Past 2000 Years in the West Lake, Hangzhou

于 1991年在西湖湖底作 15个深度 1m左右的钻孔 ,根据其内微化石藻的垂直分布探索西湖近 2 0 0 0年藻类种群的演替 ,并藉此反映湖泊的古生境及其富营养化发展的历程 ,结果显示淡水西湖形成后藻类的垂直分布由下而上可分为 3带 :( 1)附生藻带 (短缝藻 -桥穹藻 -异极藻组合 ) :- 85cm至 - 4 5cm,以喜酸性及真酸性的附生藻为主 ,适应于当时的沼泽生境 .( 2 )附生藻向浮游藻过渡带 (水花束丝藻 -直链藻组合 ) :通常在 - 30 cm至 - 4 0 cm层段 ,以不定性成分为主 ,并有少量喜碱性藻种出现 ,湖体显示中营养状态 .( 3)浮游藻带 (缢缩脆杆藻凸腹变种 -四尾栅藻-螺纽鞘丝藻组合 ) :- 30 cm以上 ,以喜碱性藻种为优势 ,藻量增大进入富营养化时期 .到 - 10 cm上下层段喜碱性藻种藻量形成峰值 ,显示进入超富营养化时期 .- 10 cm以上残骸量略有降低趋势 ,这与 2 0世纪 80年代之后对西湖富营养化采取截污。

Fifteen One meter deeped cores were drilled in West Lake, Hangzhou, in 1991. The vertical distribution of microfossil algae in the sediment were analyzed, in order to study the algae succession and trophic developing process of West Lake. Three zones were divided as follows: (1) Epiphytic algae zone ( Eunotia spp. Cymbella spp. Gomphonema spp. assem.):-85cm to -45cm deep, mainly made up of acidobiotic and acidophilous species which were suitable for the bog stage in 2000 years ago. (2) Transitive zone from epiphytic algae to phytoplankan ( Aphanizomenon flos aquae Melosira spp. assem.):usually existed in a depth between -30cm to -40cm, consisted of indifferent species combining with some alkaliphilous species, indicating that the lake had entered into mesotrophic stage. (3) Phytoplankton zone ( Fragilaria construens var. venter Scenedesmus quadricauda Lyngbya contorta assem.): At the depth of -30cm and above alkaliphilous species became the dominant species and its density were increased indicating that the lake had been entered into eutrophic stage. Around the depth of -10cm, the density of microfossil algae reached the peak value, representing a hypertrophic stage of West Lake. At the depth of -10cm and above, the density of microfossil algae were decreased, which maybe relative to the government's comprehensive control of eutrophication after 1980.