龟石水库夏季富营养化状况与蓝藻水华暴发特征

Eutrophication and Characteristics of Cyanobacteria Bloom in the Summer in Guishi Reservoir

龟石水库是贺州市主要的饮用水源,2014年夏季第一次暴发大规模的蓝藻水华.本研究通过分析水体的富营养化时空变化规律、外源污染来源以及浮游藻类群落结构动态变化特征,进而评价水体的富营养化状况,并提出合理的防控措施.结果表明,水库的氮磷浓度逐年升高,TN含量已远超过地表水Ⅱ类标准,部分样点的TP含量也超过Ⅱ类标准,且主要来源为规模化养殖和农业面源污染.水华期间浮游藻类细胞密度变化范围为8.60×10~6~5.36×10~8cells·L^(-1),水华优势种为惠氏微囊藻,密度最高达到5.36×10~8cells·L^(-1)以上,叶绿素a浓度最高为74.48μg·L^(-1),惠氏微囊藻细胞密度随时间推移呈现逐渐降低的趋势,并且垂直方向集中分布在表层及水下2 m处.水华期间浮游藻类总细胞密度与TN、TP、NO_3^--N和高锰酸盐指数呈现显著正相关,与透明度呈显著负相关.微囊藻毒素监测结果表明龟石水库水质未受到微囊藻毒素的污染.综合分析,对于中营养水平的龟石水库而言,蓝藻水华的防控既要关注气候和气象条件,更要尽量削减氮、磷营养盐入库量,维持较低营养盐水平是防范蓝藻水华的关键.

Large-scale cyanobacteria bloom occurred in the summer of 2014 in the Guishi Reservoir that is an important drinking water source for Hezhou City. The dynamic change regularity,external pollution sources,and the phytoplankton community characteristics during the bloom were investigated to evaluate the eutrophication in the reservoir and to present effective prevention and control measures. The results showed that nitrogen and phosphorus concentrations increased year by year; water quality on some sites has been out of class Ⅱ of national water quality standards; and the main pollution source was the agricultural non-point sources. Phytoplankton cell density was in the range of 8. 60 × 10^6-5. 36 × 10^8cells·L^-1and chlorophyll a concentrations reached 74. 48 μg·L^-1during the bloom. The dominant species was Microcystis wesenbergii whose density reached 5. 36 × 10^8cells·L^-1. The cell density decreased over time and concentrated on the surface and at the depth of 2 m underwater. The total phytoplankton cell density was strongly correlated to total phosphorus,total nitrogen,nitrate nitrogen,and the permanganate index,and was inversely correlated to transparency. The water in the Guishi Reservoir was not polluted by microcystic toxins. Moreover,Guishi Reservoir is in a meso-eutrophic state; therefore,the prevention and control of the cyanobacteria bloom should focus on weather conditions and on reducing the input of nitrogen and phosphorus to keep the nutrient levels low.