低水位运行对天目湖水库水质与生态的影响

摘要

2008年8月天目湖沙河水库开始进行除险加固施工,施工期间水库平均水位比2004-2008年平均值低1.73 m,对此期间水质、浮游生物等变化情况进行实地监测,研究低水位运行对沙河水库水质和生态的影响.结果表明,2008年9月-2009年8月低水位运行期间,水体对于外源营养盐输入的缓冲能力减弱,p(TN)浓度峰值与强降雨过程有关,1次早春暴雨(2009年2月17日-2月27日)即导致水体p(TN)由0.92升高到2.09 mg· L-1,直到夏季暴雨期后才回归正常；ρ(TP)主要受浮游植物生物量和悬浮物含量影响,低水位运行对其影响不大；2009年夏季浮游植物中蓝藻门比例明显高于2008年同期,说明整体藻类群落结构向偏富营养化状态转化；2009年6-8月原生动物平均丰度为1 730 L-1,轮虫为4 188 L-1,轮虫丰度较2008年同期增加近1倍,桡足类平均丰度较2008年同期下降21％,枝角类丰度变化剧烈；2009年夏季水库水体Chl-a营养状态指数高于2008年同期.总体而言,低水位运行期间整体生态系统的脆弱性增强,浮游动物、浮游植物、营养盐等生态系统基本要素的波动大大增加,环境条件变化对水库的冲击效果变得更加明显.因此,在水库的水质和生态管理中,需注意保持安全的水位.%Effects of low water level on water quality and ecology of the Tianmuhu Reservoir, Liyang, China were evaluated by means of high-frequency in situ monitoring of the water quality and plankton in the reservoir during the period from September 2008 till August 2009, when the water level of the reservoir was lowered down by 1. 73 m below the mean water level of the years 2004 - 2008 for reinforcement. It was found that the reservoir weakened its buffering capacity of incoming exogenous nutrients in that year of low water level operation. Peaks of TN concentration was closely related to heavy rainfall. One early spring heavy shower ( Feb. 17 - 27 , 2009 ) immediately led to a sharp rise of the p( TN ) of waterbody from 0. 92 to 2. 09 mg · L~l , which returned to normal only after the end of the summer storm season. TP concentration in the waterbody was mainly affected by the biomass of plankton and the content of suspended substances therein and little by the low water level. In the summer of 2009, the proportion of Cyanophyta among the phytoplankton was obviously higher than that in the summer of 2008, suggesting that the entire alga community structure tended towards that under eutrophication. Compared with that in June August, 2008, the mean abundance of protozoa was 1 730 L~-1 and of rotaria 4 188 L-1, in June August, 2009, almost doubled, that of copepod decreased by 21% but of cladocera fluctuated sharply. Moreover, the Chl-a nutrition index of the waterbody increased. In general, low water level makes the whole ecological system more fragile, and the fundamental elements of the ecosystem, such as zooplankton, phytoplankton and nutrients, fluctuate more sharply, and the waterbody more susceptible to changes in environmental conditions. It is, therefore, suggested that it is essential to keep a suitable water level in management of reservoirs in terms of water quality and ecology.