富春江水库变动回水区蓝藻水华成因初探

Preliminary Study on Causes of Cyanobacteria Blooms in Fluctuating Backwater Area of Fuchunjiang Reservoir

以富春江水库蓝藻水华为研究对象,对变动回水区生态水文特征开展调查。结果表明,受上游多年调节型水库千岛湖下层滞水泄流和兰江自然来水影响,富春江水库库尾存在显著的温差异重流。源自千岛湖的低温水在密度差的影响下沿富春江水库底部向下游流动;水温相对较高的兰江水则以表层流的形式在水库库尾做往复运动。这种异重流结构为蓝藻生长创造了良好的水动力、光照和营养盐条件。此外,水库库尾流速减弱导致大量泥沙发生沉降,使得此处水体透明度提高,水下光传输能力增强,从而使表层水体中的蓝藻快速增殖,并在长水力停留时间作用下累积形成水华,进而影响溶解氧的垂向和纵向分布。本研究可为其他水库变动回水区富营养化形成机理研究提供参考。

Taking the cyanobacteria blooms of Fuchunjiang Reservoir as the research object,the ecological hydrological characteristics of the fluctuating backwater area were investigated.The results show that due to the effects of the flow discharge in the lower layer from the Qiandao Lake,a multi-year regulating storage reservoir in the upstream and the natural inflow of the Lanjiang River,there is a significant thermal density flow in the reservoir tail of the Fuchunjiang reservoir.The low-temperature water from Qiandao Lake flows downstream along the bottom of Fuchunjiang Reservoir under the impact of density difference,while the Lanjiang River with relatively high water temperature reciprocates at the end of the reservoir in the form of surface flow.This thermal density flow structure creates good hydrodynamic,light and nutrient conditions for the growth of cyanobacteria.The decreasing of the flow velocity at the tail of the reservoir leads to the sedimentation,which makes the transparency of the water improved and the transmission of light is enhanced at underwater area.The cyanobacteria living in the surface waters rapidly proliferate under the supply of adequate nutrient salts,then accumulate and form blooms under the long hydraulic retention time,thereby affecting the distribution of dissolved oxygen.This study can provide a reference for the study of eutrophication mechanism in other fluctuating backwater areas of reservoirs.