三峡水库神农溪2014年春季浮游藻类演替成因分析

Causes of succession of planktonic algae in Shennong bay of Three Gorges Reservoir in spring in 2014

摘要:

[目的]研究三峡水库神农溪库湾春季水华期间浮游藻类演替及其成因分析。[方法]2014年3-5月在神农溪库湾布置了6个断面（SN01-SN06），在神农溪汇入长江干流河口附近水域设置1个断面CJBD，对浮游藻类、相关环境因子及水动力因子进行了同步监测，据此分析了水体层化结构及水动力特性。[结果]神农溪在监测时段内共检测到浮游藻类6门38种（属）；库湾浮游藻类生物量时间上差异显著（ANOVA，P<0.05）。春季浮游藻类群落结构具有明显的演替规律，3月份暴发大面积的硅藻水华（藻密度>100×10⁵ cells/L），小环藻（Cyclotella spp.）为优势藻种；4月在SN02-SN06暴发以小球藻（Chlorella spp.）为主要优势种、衣藻（Chlamydomonas spp.）为次优势种的绿藻水华（藻密度>100×10⁵ cells/L），5月份受水位大幅消落影响，浮游藻类生物量降低且无明显优势藻种。[结论]在具备充足的营养盐的水体中，水体层化结构与水动力特性对浮游藻类演替影响重大。三峡水库水位处于快速消落阶段时，流速成为抑制神农溪库湾藻类生长的主要因素。

Abstract:

[Objective] Algal blooms occurred in some sections of Shennong bay after impounding of Three Gorges Reservoir. [Methods] Related environmental and hydrodynamic factors were monitored during the period of algal blooming season in 2014 (March 20, April 13, May 23) in Shennong bay, Three Gorges Reservoir. To study succession of planktonic algae, water stable coefficient, euphotic depth and mixed layer depth were used to analyze stratification and hydrodynamic characteristics. [Results] We identified 6 phyla, 38 species (genera) planktonic algae. The sensitive area of algal bloom was at SN05 (677.677×10⁵ cells/L) and SN06 (716.761×10⁵ cells/L), and the planktonic algae biomass during this period was significantly different (ANOVA, p<0.05). Moderate water temperature, adequate nutrients, weak stratification and poor mixing promoted the rapid growth and breakout of the diatom bloom with Cyclotella spp. as the dominant species in March. Further increase of water temperature, stronger stratification and decrease of dissolved silicate and mixing layer restricted the diatom growth. Chlorella spp. and Chlamydomonas spp. grew better in shallow mixed layer with rich nutrients and evident stratification. Then Chlorophycean bloom broke out with Chlorella spp. as the dominant species and Chlamydomonas spp. the next-dominant species. High biomass maintained in April. In May, algal bloom gradually vanished due to sharp fluctuation of water level and increase of velocity. Monitored maximum water velocity was 0.1141 m/s at 2 m depth, exceeded an optimal flow rate perfect for growth of planktonic algae. [Conclusion] Stratification and hydrodynamic characteristics had important effect on planktonic algae under the condition of adequate nutrients. Velocity became the main factor that inhibited the growth of algae in Shennong bay in pre-flood falling stage of the Three Gorges Reservoir.