南水北调中线调水对密云水库产嗅藻生长影响研究

Miyun Reservoir, the most important surface source water for Beijing, has been suffered water crisis due to continuous drought and over-extraction during recent years; the Central Route of South-to-North Water Diversion Project (SNWDP) is expect to transfer water from Danjiangkou Reservoir to Miyun Reservoir in order to resolve the water shortage. The SNWDP will be bound to solve release the water crisis in the respect of “water quantity”, however, the “water quality” should also be guaranteed. This project is aiming to assess the impact of the SNWDP on the water quality of Miyun Reservoir, in a view of taste & odor problem in drinking water – a long term problem in Miyun Reservoir; the laboratory simulation, field monitoring as well as model computation were performed in this project to evaluate the impact from SNWDP on the water environment, including the mixing effect between south water and reservoir water, the water environmental changes caused by the water level increase as well as the invasion of external algal species from south water. Based on these results, the environmental parameters of Miyun Reservoir were determined according to the model simulation, and the growth potential of Planktothrix sp. and the trend of taste & odor problem in Miyun Reservoir were evaluated according to ecological niche theory; this project will assess the water quality of Miyun Reservoir after the execution of SNWDP, and is believed to be helpful for scientific policy adoption and effective strategies exploration.

密云水库为北京市最重要的地表水水源地，近年来由于长期干旱与超采，存水量严重不足；为缓解密云水库水危机，南水北调中线预计于2015年向密云水库输水。然而，调水在解决了“水量”问题的同时，还需要保证“水质”达标。本项目以评估调水对密云水库水质影响为研究目标，结合多年来密云水库固有的饮用水嗅味问题，从多方位采用实验模拟，原位监测、模型计算等方法全面分析中线调水对密云水库水环境的影响，包含调水引起的水体混合对密云水库水质的直接影响，调水后由于水位上升导致水环境的变化，以及由于外来藻种引入对密云水库藻类群落结构的冲击。在此基础上，综合以上各点，采用模型模拟计算调水后水环境各项参数，最后利用生态位理论评估新环境下浮颤藻的生长潜力以及水库嗅味问题的发展态势，从而为全面评估调水后密云水库供水水质、制定科学合理的应对方案、探索有效的控制策略提供支撑。

南水北调中线于2015年向密云水库输水，已补充长期干旱及超采导致的失衡水量。本项目通过原位监测中线明渠水质、藻类及致嗅物质情况，掌握了中线水源的主要水质情况及风险，发现藻类经过长距离明渠输送后有显著增加现象，主要产生原因可能是在明渠河北至北京段流速降缓，有利于藻类生长繁殖；同时，针对密云水库嗅味问题，构建了产嗅藻与致嗅物质之间的分位回归模型，用于评估不同产嗅藻浓度水平下水库出现嗅味问题的风险；结果表明，发现当水体中浮颤藻的浓度高达4.0 × 10⁵ cells/L时，水体中嗅味物质的浓度超过嗅阈值(15 ng/L)的概率高达90%;而如果能将水体中浮颤藻 的浓度控制在1.6 × 10⁴cells/L以下时，水体中出现嗅味问题将小于10%；该研究内容的成果有利于加深对湖库中浮颤藻的生长与产嗅行为的理解，同时能为 湖库型水源地出现由于深水型产嗅蓝藻生长引起的嗅味问题提供更多的知识以及重要的科学管理依据。最后，针对密云水库开展了浮颤藻的生态位解析及中线调水后水库产嗅潜力评估。根据生态位理论模拟结果，由于含氮量相对较高的丹江口水库的水体输入至密云水库引起的氮浓度升高后，密云水库水体中产嗅浮颤藻的生长潜力很可能会上升。该研究内容的结果基于生态位理论得出，有利于进一步理解密云水库中藻类群落竞争与演替过程，同时也为湖库型水源地的水 质管理中嗅味问题发生风险的评估提供十分重要的科学工具。