三峡水库香溪河库湾蓝藻水华生消过程初步研究
Preliminary Study on Cyanobacterial Bloom in Xiangxi Bay,Three Gorges Reservoir
-
摘要: 2008年6月三峡水库部分支流库湾第一次暴发大面积蓝藻水华,表明水库支流库湾生态环境已经恶化。以香溪河库湾为例,于2008年6月6日~7月25日,每间隔7天在库湾14个采样点采集水样一次,对蓝藻水华进行监测,研究蓝藻水华生消过程及其影响因素。结果表明,这次水华自2008年6月9日暴发,6月20日达到顶峰,7月11日结束,持续大约1个月;综合营养状态指数(TSI)与叶绿素a(Chl.a)所指示的水体营养状态,将同时满足TSI>60与Chl.a>20μg/L两个条件的区域边界视为蓝藻水华暴发的临界状态;整个水华暴发过程大致可分为两个阶段:6月9~25日和7月3~11日。水华暴发区域主要集中在距河口20~30km处相对稳定的库湾中上游区域,适宜的水动力条件是水华暴发的必要条件。此次水华的消落过程主要受到磷含量降低的限制以及氮磷比的影响,当氮磷比显著升高时,蓝藻的生长受到抑制。总氮总磷比在10~25之间比较适宜蓝藻的大量生长,因此限制磷元素的入库通量对于预防和控制库湾水华的暴发具有重要意义。Abstract: A large-area cyanobacterial bloom was observed for the first time in some bays of Three Gorges Reservoir(TGR) in June 2008,which indicated the deterioration of the aquatic ecosystem.Thick blooms covered most parts of Xiangxi Bay that is a classical bay of TGR on 20 June 2008.Fourteen sampling sites were monitored weekly from 6 June to 25 July 2008,to study the dynamics of the algal bloom in the bay.The whole process of this algal bloom and some influencing factors were analyzed in this paper.The results showed that the bloom broke out on about 9 June 2008;and reached the summit on 20 June and ended on 11 July,lasting for about a month.According to Carlson's Trophic State Index(TSI) criteria,Chl.a content is equal to 20 μg/L and TSI is 60 are the critical values of cyanobacterial predominance.In the present study,the intersection of Chl.a content is more than 20 μg/L and TSI is more than 60 were set as the threshold state of the cyanobacterial bloom.According to the criteria,the whole process of the bloom could be divided into 2 stages:9-25 June was the first stage and 3-11 July was the second stage.The zone of the algal bloom was mainly concentrated in the region about 20-30 km away from the river mouth,namely the middle-upper reaches of the bay.This indicated that suitable hydrodynamic conditions were necessary to the outbreak of the cyanobacterial bloom.Low phosphorus and high N/P were the main factors limiting the bloom.When phosphorus content decreased and N/P increased significantly,the growth of the cyanobacteria was suppressed.The results also preliminarily indicated that N/P within the range between 10:1 and 25:1 was more favorable to the growth of the cyanobacteria in this area.So,decreasing the input of the phosphorus is of great importance to prevent or control the algal blooms in Xiangxi Bay.