三峡水库支流小江富营养化模型构建及在水量调度控藻中的应用

三峡水库蓄水以来,支流小江呈富营养化加重的趋势,且多次暴发春季水华.水库蓄水以后支流流速变缓,水体滞留时间增加,是引发支流水华的主要因素之一.基于MIKE软件,建立小江调节坝下游至河口的二维水动力-富营养化模型,考虑碳、氮、磷3种元素在浮游植物有机体、死亡腐屑和无机盐中的循环转化,模拟小江河段的春季水华过程.分析小江生态调节坝的水量调节抑藻作用,即人为制造"洪水脉冲",增加短时间内的水流流速,对下游流场进行扰动以控制水华.计算结果表明,增大泄水量对调节坝下游的小江河段的春季藻华总体上具有一定的抑制作用.小江上游河段调度作用效果明显,下游高阳至入汇口河段调节作用较小,上游调节坝水力调度可以作为三峡水库支流水华应急治理措施之一.营养盐控制应该是控制支流水华的根本措施.

Numerical simulation of eutrophication and its test of ecological operation schedule in Xiaojiang River, the tributary of Three Gorges Reservoir

Xiaojiang River, the tributary of the Three Gorges Reservoir, has suffered from eutrophication since the impoundment in 2003. Previous study showed that the lower river velocity and longer residence time are the key factors which promote the phytoplankton spring bloom. A two dimensional hydraulic and eutrophication model was developed to investigate the hydraulic and eutrophication dynamics in Xiaojiang branch. The model describes cycling of three nutrients element, namely carbon, nitrogen and phosphorus, in phytoplankton, detritus and inorganic nutrient. The effect of the hydraulic regulating of the sub-reservoir on dominance of the spring bloom was examined numerically. Artificial flood-impulse from the sub-reservoir is arranged to promote the physical disturbance in downstream river. The model predicts that flushing with water from the sub-reservoir will suppress phytoplankton blooms to some extent when the flushing water quantity is sufficiently increased. The effective suppressing river reach is the upper reaches of Gaoyang. While in the reach below Gaoyang, there is no obvious response of the phytoplankton growth to the hydraulic regulating. The eco-operation of the upstream reservoir can be used as one of the emergency alternative management for controlling the algal bloom in Three Gorges Reservoir. In order to control algal blooms in the tributary, nutrient loading should be reduced significantly.