降雨对蓝藻水华消退影响及其机制分析

Effect of the Rainfall on Extinction of Cyanobacteria Bloom and Its Mechanism Analysis

2016年5月24日至6月2日香溪河库湾经历了3次不同强度的降雨,对降雨前后库湾水流、水温、光学特性、叶绿素a浓度等因素进行分析.结果表明,5月27日中雨期间,较降雨前库湾上游来流量增加1.9倍,库湾平均混合层深度增加8.2 m;6月1日小雨期间,较降雨前库湾平均混合层深度增加1.6 m,平均叶绿素浓度降低2.02μg·L^(-1);6月2日大雨期间,较降雨前库湾上游来流量增加4倍,库湾平均混合层深度增加7.9 m,平均叶绿素浓度降低14.64μg·L^(-1).降雨导致上游来流量增加,加快了藻类的迁移;混合层深度增加破坏了藻类的生长环境,是水华消退的主要原因.降雨结束后,在2~3d适宜光照、温度条件下库湾水体水温分层恢复,藻类快速生长繁殖,导致库湾表层叶绿素a浓度回升,降雨对水华的暴发具有阶段性抑制作用.

There were three rainfall events with different intensity in the Xiangxi Bay（ XXB） from May 24 to June 2 in 2016. The factors such as hydrodynamics,water temperature,optical properties,and chlorophyll a concentrations during the rainfall events were analyzed. During the May 27 moderate rain period,the upstream flow of the reservoir bay increased by 1. 9 times and the average mixing layer depth in the whole reservoir increased 8. 2 m,compared to those before the rainfall event. During the June 1 light rain period,the average mixing layer depth in the whole reservoir increased 1. 6 m and the average chlorophyll concentration reduced 2. 02μg·L^（-1）,compared with those before the rainfall event. During the June 2 heavy rain period,the upstream flow of the reservoir bay increased by 4 times,the average mixing layer depth in the whole reservoir increased 7. 9 m and the average chlorophyll concentration reduced 14. 64 μg·L^（-1）,compared with those before the rainfall event. The algae moved from the upstream to the downstream with water that reduced the concentration of algae in the XXB. The water temperature stratification weakened during the rain event and the average mixing layer depth in the whole reservoir increased,destroying the algal growth environment. After the rainfall,under suitable light and temperature conditions for 2-3 d,the water temperature stratification of the reservoir was recovered and rapid growth and reproduction of algae occurred. As a result,the chlorophyll concentrations in the reservoir increased. Rainfall has a periodic inhibitory effect on the outbreak of algal blooms; however,it cannot fundamentally solve the problem of tribal bay blooms.