|关键词: 太湖 水华 微囊藻 风集作用 水华控制
|Algal bloom in Taihu Lake and its control
Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008
|In Taihu Lake, algal bloom is caused by blue-green algal microcystis, occuring in summer and autumn, and distributing mostly in the northwestern area.This lake has nutrient loading of 12-0 g N/(m2·a)and 0.85g P/(m2·a), and a nutrient store of 62.3 g N/(m2·a)and 41.0 g P/(m2·a)m in the 5 cm surface layer of sediments.Due to its shallowness and strong disturbance of wind-waves, the lake provides sufficient nutrients for the algae-In summer, the algae has a daily P/B ratio of 0.92, a net productivity equal to 20960 t/d of fresh algae, and consumes as much as 167.3 t N and 15.85t P every day.Wind-crowding effect of the buoyant algae results in heavy alage bloom in the northwestern area, and it forms a Special biological nutrient filter' which prevents nutrients in the lake water from being brought out by the outflow currents and enhances nutrient accumulation in the lake.Strong disturbance of wind-waves can break algal bloom and limit the light availability of algae.Sharp decrease of macro-zooplankton may enhance algal bloom in the lake.The algal community developed following Logistic Equation dN/dt=N·r(1—N/K) (r=0.0215 /d, K=60000t) from Feb.to Aug.in 1991-Although it is difficult to reduce K by nutrient control in a short rime, it may be possible to reduce N or r by algal removal or by regulating some ecological factors in the lake.By harvesting algae, not only can the amount of algae in the lake be effectively controlled, but also large amount of nutrients be removed.By elevating water level, r may be reduced because the net productivity may be.decreased by adding a respiratory layer in the bottom.Protecting zooplankton to increase its grazing pressure on algae may be a good way to reduce r; but it needs further studies to prove if silver carp can be used to contol blue-green algae in this lake.
|Key words: Taihu Lake algae bloom microcystis wind-crowding water bloom