Key issues of water quality improvement in the landscape lake of plain river network and corresponding countermeasures: a case study of Nanhu Lake in Jiaxing City

Nanhu Lake in Jiaxing City is the birthplace of the Communist Party of China and the place where revolutionary red ships set sail, and the “beautiful water” of Nanhu Lake is very important. In 2018, the water transparency of Nanhu Lake was less than 30 cm, with poor senses and high levels of nitrogen and phosphorus in the water, which cannot meet the water environment functional areas goals and objectives, i.e. Grade Ⅲ of Environmental Quality Standards for Surface Water(GB 3838-2002). The characteristics and environmental status of Nanhu Lake water system were analyzed and the overall improvement of water quality of Nanhu Lake was taken as the goal, focusing on the reduction of suspended solids content and improvement of water transparency, and insist on the principle of the combination of pollution control and ecological restoration, the protection and restoration measures were proposed. These measures included five aspects, including source control, construction of clear water into the lake corridor, enhanced purification of the estuary, improvement of biological environment and long-term management, in order to restore the water ecosystem of Nanhu Lake to a virtuous cycle, and finally achieve the beautiful water environment of Nanhu Lake.