南亚热带大型贫营养水库浮游植物群落结构与季节变化——以新丰江水库为例

Phytoplankton assemblage and seasonal dynamics in the large oligotrophic Xinfengjiang reservoir in southern China

新丰江水库是我国第四大的水库，也是广东省最大的水库和重要的水源地。于2004～2005年2月一次调查了新丰江水库水文、水质和浮游植物分布，分析了浮游植物群落季节动态特征。新丰江水库浮游植物生物量比较低，在0．037—1．497mg·L^-1之间变化。浮游植物种类较多，11次采样共检到158种。在丰度上，水库浮游植物主要以小环藻、蓝纤维藻、小球藻和纤维藻等优势种为主，而在生物量上则以微小多甲藻为优势。浮游植物组成随季节变化而不同，春季以硅藻、甲藻和绿藻为优势类群；夏季以蓝藻、绿藻和硅藻为优势类群；秋季蓝、绿藻减少而硅藻和甲藻增加。2004年的浮游植物季节性变化更为明显，有从硅藻-绿藻优势（2月和4月份），到蓝藻-绿藻优势（6月和8月份），到混合优势（10月份）和金藻优势（12月份）这样一个变化过程。2005年硅藻的相对丰度比2004年高出很多。两年浮游植物组成的差异与两年的降水量有关。水动力学对丰水期（6～8月份）浮游植物组成结构有较大影响，导致硅藻和绿藻相对丰度的增加。与温带贫营养型水库相比，新丰江水库的浮游植物群落具有春季和秋季种类多、夏季的蓝藻种类丰富的特点。从细胞大小分布上看，小于20μm浮游植物是生物量的主要贡献者，其次是大于45μm的浮游植物。在粒径小于20μm的浮游植物中，微小多甲藻是最主要的贡献者。浮游植物群落的大小分布受水动力学条件和营养盐浓度动态的影响。

Xinfengjiang reservoir is the largest reservoir in Guangdong Province and an important regulator of regional water resource. In the years 2004 to 2005, phytoplankton （ species composition and total biomass） and environmental variables were monitored in this oligotropical water body every two months. The phytoplankton biomass varied from 0. 037 - 1. 497 mg·L^-1, and 158 species were observed. Dominant phytoplankton were Cyclotella meneghiniana, Dactylococcopsis rhaphidioides, chlorella vulgaris and Ankistrodesmus sp. , but Peridinium pusillum was the greatest contributor to biomass. The specific composition of phytoplankton community displayed a seasonal pattern. Diatoms, and Dinoflagellates dominated in the early spring and together with Chlorophyta, they dominated in late spring. Cyanophyta, Chlorophyta and Bacillariophyta dominated in summer. In autumn, the abundance of blue-green and green algae decreased while diatoms and dinoflagellates increased. The seasonal variation of dominant phytoplankton groups was greatbr in 2004 than in 2005. Diatom and green algae dominanted in February and April; Cyanobacteria and green algae dominanted in June and August; diatom, Cyanobacteria and green algae were abundant in October, and Dinobryon in Chrysophyta dominanted in December. There existed a recognizable annual difference in phytoplankton community. Relative abundance of diatioms was much higher in 2005 than in 2004. It is likely the difference in yearly precipitation levels accounted for the differences in yearly phytoplankton abundance and biomass patterns; Hydrodynamics especially in the flood season （June to August） is likely the cause of the increase in diatoms and green algae,. Phytoplankton species having a diameter less than 20 m were the main contributors to total biomass, and those having a diameter greater than 45μm were the secondary contributors. Peridinium pusillum was the dominant species when diameters were less than 20μm. Xinfengjiang Reservoir can be characterized as having more cyanobacteria species （Microcystis and Psuedanabeana ） than other oligotropical temperate reservoirs. Biomass sized composition of the phytoplankton community displayed a seasonal dynamics following hydrodynamics and nutrients.