高州水库水位上升期坝前深水区浮游植物群落的响应特征

Responses of phytoplankton community to increasing water level in the lacustrine zone near the dam of a large tropical reservoir: Gaozhou Reservoir,South China

我国南亚热带地区从5月初开始进入汛期,充沛的降雨导致入库和出库流量发生较大变化,水位升高,从而显著地改变水库的水文和水动力状态,进而影响水库水质和浮游植物群的结构.以位于广东西部(粤西)的大型水库——高州水库为对象,于2012年5-10月对水库供水区进行逐月分层采样,分析水库水位上升时期浮游植物在垂直方向的群落结构特征及其动态变化.结果显示,6-7月份为水位主要的上升期,一个月内水位上升4 m,经历了从低水位到高水位的快速转换,7月份之后水位趋于平稳.快速的水位上升改变了水体的温度结构和分层,导致混合层变浅且湖下层深度增加,进而改变光和营养盐可获得性及水体垂直pH值分布.水位上升前和上升后水体pH值、透明度、营养盐(氮、磷)浓度有显著差异(P<0.05).浮游植物生物量主要由硅藻和绿藻门的种类所贡献,优势种由硅藻的种类向绿藻的种类演替:由梅尼小环藻(Cyclotella meneghiniana)、模糊直链藻(Melosira ambigua)转变为亮绿转板藻(Mougeotia laetevirens Wittrock),再到钝角角星鼓藻(Staurastrum retusum),pH值、溶解态磷和光的可获得性是影响浮游植物群落结构的主要因子.水位上升前、上升期间、稳定后的优势功能群分别为B、T和NA功能群,水体混合及其导致的光可获得性的改变是浮游植物功能类群发生改变的主要原因.研究表明,浮游植物群落对大幅的水位上升有明显的响应,因生境的改变出现明显的群落演替,而对小幅(<1 m)的水位波动响应不明显.

Abstract The Gaozhou Reservoir is an important water body located in the western region of Guangdong Province. High precipitation in the catchment leads to significant fluctuations of inflow, outflow and water level in wet seasons. To understand the responses of phytoplankton community to such strong fluctuations, structure of phytoplankton community and its dynamics in epilimnion and hypolimnion were investigated monthly from May to October 2012 when water level rapidly shifted from low to high level. Our investigation showed that water level quickly rose by 4 m in one month from June to July, and became stable since July. This scenario influenced the vertical profile water temperature and stratification, with shrinking mixing lay and expanding hypolimnion, and induced the variation in pH and availability of nutrients and light intensity. There existed a significant difference in pH, SD total nitrogen and total phosphorus concentration （P 〈 0.05） before and after water level rising. The phytoplankton community was mainly dominated by diatom and chlorophyta, and the dominant species changed from Cyclotella meneghiniana and Melosira ambigua to Mougeotia laetevirens Wittrock, then to Staurastrum retusum with increasing water level. The primary factors for modifying phytoplankton community structure were pH, phosphorus and light availability. The representative functional groups of phytoplankton before, during and after water level rising were B, T and NA, respectively. The variation of mixing pattern and availability of light was the primary explanation for succession of functional groups. In conclusion, phytoplankton community actively responds to the high water level increasing with observable succession, and weakly responds when water level rising is below 1 meter. Highly increasing water level changed the ecological condition （i.e. niche）, then lead to a clear succession of phytoplankton community.