Sub-theme
4. Supporting Aquatic Ecosystem Health and Functions
Topic
4-8. Water quality improvement
Body
After fierce fight against water pollution for several decades, much progress has been achieved in Taihu Lake basin. While polders in plain river network region, especially for those with high water consumption industries, struggled to polish water environment in a variety of ways. Water transfer and diversion from outside of polder is the commonly utilized method to alleviate polder water pollution, which has been proved to be effective by researchers. However, some people argued that water diversion only transferred pollutant from one place to another, which makes no sense of environmental quality. In this paper, we selected Yuejin Polder, a typical area in Suzhou City, to expolre whether water diversion could polish water quality in the polder, and the needs for regulation of gates and pumping stations.Hydrological gauges and automatic water quality monitoring stations had been installed, and field prototype synchronous monitoring experiment was carried out. Mathematical model of hydrodynamics, water age, and water quality of the Yuejin Polder river network were constructed.The concentration of pollutants in rivers inside and outside the polder showed certain spatiotemporal heterogeneity. The average concentration of total phosphorus(TP) in the flood season and non-flood season in the polder is 0.28mg/L and 0.15mg/L respectively, and TP inside the polder is higher than that outside the polder. During the water diversion test, when there is a blockage point (Yongji Port) or captured rivers (Wujinbang), the water quality is poor. The model calculation results show that the water exchange time(WET) of the polder river network is within 5 days. Under different water diversion schemes,the better the water connectivity, the shorter the WET. In water diversion Scheme 5, when 4 gates were opened and Yongji Port was connected, the WET of captured rivers were still more than 5 days, and the concentration of ammonia nitrogen was still high. The spatial distribution trend of water quality index concentration is basically consistent with the spatial distribution trend of WET. A single regulation method is more likely to cause differences in the connectivity and the spatial distribution of water quality in the river network, forming local stagnant water areas or dead water areas, leading to deterioration of water quality.On the basis of regional pollution source control, a scientific scheduling method of multi-source water diversion can be adopted to strengthen its water flow and water exchange capacity and improve the quality of the water environment in plain river network area.