Status, causes, and management of water environment in polders of middle-lower Yangtze River

Polders in middle-lower Yangtze River are important food production bases and population gathering areas, as well as important wetlands.However, they are now facing severe eutrophication caused by excessive nitrogen and phosphorus.Through historical data collection and in-situ monitoring, as well as a systematically review of researches on the eutrophication of polder waterbodies, the paper discussed the current status and possible reasons of the water environment in polders.Results show that nitrogen pollution was more severe than phosphorus.Lakes and ponds had higher nutrient concentrations than ditches and rivers.Polders in Taihu and Chaohu Lake had higher eutrophication level than Dongting and Poyang Lake.1980s and 1998 The evolution of water environment was divided into 3 phrases: before 1980s, 1980s-1998,after 1998.Flood control and water use activities weakened the hydrological connectivity between waters in and out polders, as well as lateral, longitudinal, and horizontal connectivity between the internal water bodies.Storing floodwater and building environmental reservoirs could coordinate the relationship between water environment, water disasters, and water resources.The research can provide basis for water environment management in polders.