Abstract:In order to explore the water quality characteristics of Daheiting Reservoir after the removal of fish cage in 2017, the surface water samples and stratified water samples of the reservoir were collected in 2018 to analyze the spatio-temporal characteristics of the water quality of the reservoir. The results show that the total nitrogen and total phosphorus in the surface water of Daheiting Reservoir are the highest in winter and summer, and nitrate nitrogen is the main component of dissolved inorganic nitrogen. The spatial distribution characteristics of total nitrogen, nitrate nitrogen, total phosphorus and phosphate concentration in Daheiting Reservoir are the highest in the upper reaches, the second in the middle reaches and the lowest in the lower reaches. Ammonia nitrogen and nitrite nitrogen are opposite. Vertically, the total phosphorus concentration in the bottom layer is higher than that in the surface layer, which is related to thermocline and dissolved oxygen level. After the removal of the fish cages, the concentration of total phosphorus and phosphate, ammonia nitrogen and nitrate nitrogen in the reservoir decreased significantly, but there was no significant change in the mass concentration of total nitrogen and nitrate nitrogen. The N/P ratio shows that phosphorus is the limiting factor of the reservoir, so the removal of fish cages can effectively control the eutrophication process of the reservoir. According to the spatio-temporal distribution characteristics of water quality, the downstream water diversion should avoid taking water in winter, and the middle water column in front of the dam should be selected as the water diversion height.