Characteristics and preliminary regulating factors of cyanobacterial bloom in Xiangxi Bay of the Three Gorges Reservoir

Abstract

2008年夏季,香溪河库湾自三峡水库建库以来第1次暴发蓝藻水华,水华波及整个库湾,持续时间达1个月之余.为了解这次水华暴发特性及发生原因,本文对蓝藻水华的发生发展过程进行了跟踪调查,6-7月水华发生期间每周采样1次.调查表明本次蓝藻水华的优势种为鱼腥藻(Anabaena sp.)、铜绿微囊藻(Microcystis aeruginosa)、惠氏微囊藻(Microcystis wesenbergii)等,细胞密度高达3.82×10⁸ cells/L,蓝藻相对密度达到90%以上.本文将2008年5-7月与2007年同期理化指标比较发现,2007年5月的N:P为18.6,而2008年5月的N:P较低,为6.2,据文献报道N:P < 8有利于微囊藻的复苏,因此2008年水华前期的低N:P利于微囊藻的复苏,为微囊藻在适宜条件下的大量增殖提供了种源基础.方差分析表明,2008年5-7月各采样点真光层深度显著高于2007年同期,使得底泥中的微囊藻获得一定强度的光照而复苏,这可能是2008年蓝藻水华在香溪河库湾暴发的原因之一.综上所述,在具备充足的营养盐基础、较强的水体稳定性以及较高水温的前提下,香溪河库湾水华发生前期较低的N:P以及较高强度的光照可能是微囊藻复苏的诱导因子,为蓝藻水华暴发提供了种源基础.;A large-scale cyanobacterial bloom was observed for the first time in Xiangxi Bay in summer 2008, which lasted from early June to late July dominated by the species of Anabaena sp. Microcystis aeruginosa and Microcystis wesenbergii. The cell abundance and relative abundance is up to 3.82×10⁸ cells/L and 90%, respectively, during the peak. Controlled by nutrients, temperature and water column stability, cyanobacterial bloom in the TGR was most likely to occur in June and July. In the May of 2008, the ratio of N:P was 6.2, while 18.6 in the May of 2007. As reported, the lower N:P ratio (< 8) in the bay is beneficial to the recruitment of cyanobacteria, providing a seed resource for Microcystis to proliferate under appropriate conditions. In addition, the solar irradiance from May to July, 2008, was significantly higher than that in 2007, which may be one of the causes of cyanobacterial bloom in 2008. We supposed that on the basis of adequate nutrients, elevated water temperature and high water column stability, the low N:P ratio and high irradiance was inducible for the Microcystis recruitment, which maybe the major factors that brought about the cyanobacterial bloom.