三峡水库小江夏初水华暴发特征及原因分析

2013年5月对三峡水库小江回水区的水华发生过程进行了连续的动态监测与分析,以期了解水华过程中浮游植物群落结构的变化情况、小江夏初水华暴发特征及其主要的影响因素。期间共鉴定出浮游植物8门80属136种(含变种),以绿藻类为主(35属48种),蓝藻类(10属31种)和硅藻类(18属30种)次之,水华发生后期浮游植物及其蓝藻类的种类数少于初期和中期。浮游植物群落组成表现为蓝藻-绿藻型,且蓝藻门微囊藻占绝对优势,细胞丰度最高可达90%以上。浮游植物数量最高达10⁷cells/L以上,表层水体大于中层和底层水体。水华过程中,总氮处于重富营养水平,总磷处于轻-中富营养水平,不同水层的流速变化规律不同,其中中层与底层水体理化因子的变化特征基本一致,与表层水体有显著差异。冗余分析结果表明,浮游植物细胞总数与蓝藻数量及其微囊藻数量密切相关,与溶解氧、氮磷比等呈正相关,与总磷、流速等呈负相关,氮磷比及流速是水华发生的主要环境影响因素。

CHARACTERISTICS OF BLOOMS OUTBREAK CHARACTERISTICS AND ITS CAUSE ANALYSIS DURING EARLY SUMMER IN XIAOJIANG RIVER OF THREE GORGES RESERVOIR

Since the impoundment of Three Gorges Reservoir, Xiaojiang River has frequently occurred in the alternation of spring-summer and summer- autumn. Continuous monitoring bloom not only helps to understand the change characteristics of bloom and its influence factors, but also reflects the gradient change of water environment, which is important to understand the occurrence mechanism of bloom and the change status of the water quality. In order to understand phytoplankton community structure, blooms outbreak characteristics and their influencing factors during the progress of water bloom in early summer, the phytoplankton and physicochemical environment were monitored continuously in Xiaojiang River of Three Gorges Reservoir in May 2013. There were abundant phytoplankton with identified 136 phytoplankton species (including varieties) belong to 80 genera and 8 phyla. The main proposition of community was the species of chorophyta with identified 48 species belong to 35 genera. It was followed by the species of cyanophyta (31 species belong to 10 genera) and bacillariophyta (30 species belong to 10 genera). Comparing with the early and middle stages of water bloom, the terminal stage had less species number of phytoplankton and cyanophyta. The community of phytoplankton was characterized by cyanophyta and chorophyta during water bloom, and Microsystis were far superior numerically and the abundance up to more than 90%. The phytoplankton density could reach to 10⁷ cells·L^-1, and the density of surface water was more than the middle and bottom water in the spatial distribution. For environmental factors, total nitrogen (TN) was in heavy eutrophic level and total phosphorus (TP) was in light-moderate eutrophic level, flow velocity (FV) was varied in different layers. The physicochemical factors in the middle layer were similar with the bottom, but had significant difference with surface. Redundancy analysis (RDA) on phytoplankton and environmental factors showed that the total cell density of phytoplankton was closely related to cyanophyta and microcystis, and they were positively related to dissolved oxygen (DO) and TN/TP, and negatively related to TP and FV. This revealed that TN/TP and FV played an important role during the occurrence of water bloom of Xiaojiang River.