Study On Characteristics And Release Mechanism Of Internal Pollution In Typical Eutrophic Lakes And Reservoirs

Internationally,it is generally believed that the internal pollution load of lakes and reservoirs plays an important role in the eutrophication process of water bodies.Even when the external pollution is controlled,the internal load can still make the eutrophication problems of lakes and reservoirs last for decades.Phosphorus is the main limiting factor in aquatic ecosystems.However,the current research on the endogenous release mechanism of lakes and reservoirs is still unclear,and due to differences in hydrological conditions and sediment composition,the endogenous release mechanisms of the two lakes and reservoirs are quite different.Therefore,this paper selects the same location in the Yangtze River Delta.The Taihu Lake and Hengshan Reservoir in the region are the research objects.Through spatial survey and seasonal sampling of sediments,continuous grading extraction technology of phosphorus form,dissolved oxygen and p H microelectrode interface technology,balanced gap water sampling and other technologies are used for investigation and analysis The characteristics of endogenous pollution in Taihu Lake and Hengshan Reservoir,identify the phosphorus form and content of their sediments,analyze the release risk of endogenous pollutants of the two,and explore the release mechanism of endogenous phosphorus of the two.The main findings are:(1)The average content of total nitrogen and total phosphorus in the surface sediments of Lake Taihu is 1430 and 501 mg/kg,respectively.The pollution degree decreases from the northwest region to the southeast region.Compared with other domestic lakes,most lake areas of Taihu Lake are at a relatively serious pollution level.The total nitrogen and phosphorus pollution in Zhushan Lake and the west coast area is the most serious,at a severe pollution level.The contents of movable phosphorus and aluminum phosphorus in Zhushan Lake are the highest in the whole lake,with an average content of 431 and 380 mg/kg,respectively,accounting for 38.6% and 34.6% of total phosphorus,respectively.The diffusion fluxes of SRP and ammonia nitrogen in the northern lake area of Lake Taihu and the western coastal lake area are relatively large,ranging from 0.37 to 2.71 and 2.81 to 24.57 mg/(m2·d),respectively.There are huge differences in total phosphorus content,phosphorus form and SRP release intensity between algae-type lake areas and grass-type lake areas.(2)The average contents of total nitrogen,total phosphorus and organic matter in the surface sediments of Hengshan Reservoir are 2778 and 899 mg/kg,respectively.The content of total nitrogen and total phosphorus in the drinking water intake area of the Hengshan Reservoir and the central area of the reservoir is at a heavy pollution level,and the two inflow areas are at a moderate pollution level.The average content of total nitrogen and phosphorus in the sediment of Hengshan Reservoir is higher than that of Taihu Lake.The content of aluminum and phosphorus in Hengshan Reservoir is 152～364 mg/kg,accounting for 39% of total phosphorus on average.The removable phosphorus content is 93.5～353 mg/kg,accounting for38% of the total phosphorus on average.The release fluxes of ammonia nitrogen and SRP in Hengshan Reservoir were 3.60-42.0 mg/(m2·d)and 0.38-1.10 mg/(m2·d),respectively.(3)Select representative points in the grass-algae lake area of Taihu Lake(Zhushan Lake and Gonghu Bay)and Hengshan Reservoir to explore the release mechanism of endogenous phosphorus.The similarities between the endogenous phosphorus release mechanism in the grass-algae lake area of Taihu Lake and Hengshan Reservoir are: temperature and biological disturbance are important factors affecting phosphorus release.The mineralization of organic matter will promote the release of endogenous pollutants.Iron phosphorus,aluminum phosphorus and organic phosphorus are easily released phosphorus forms.The main reason why the phosphorus release intensity of the algae-type lake area is greater than that of the grasstype lake area may be that the content of iron,phosphorus and aluminum phosphorus in the algae-type lake area is much greater than that of the grass-type lake area,and the redox potential conditions and acid-base conditions at the bottom are more suitable for phosphorus release.The main reason why the phosphorus release intensity of the algae lake area is greater than that of the Hengshan Reservoir is that the lake area is greatly affected by hydrodynamics and has environmental factors that are more suitable for phosphorus release.In spring and summer,the water body of Hengshan Reservoir is stratified and the bottom temperature is low,which affects the release intensity of endogenous phosphorus.The main reason why the phosphorus release intensity of Hengshan Reservoir is greater than that in the grass-type lake area of Taihu Lake may be that the high content of active phosphorus in the sediments of Hengshan Reservoir,which is prone to hypoxia at the bottom,is conducive to the release of iron and phosphorus,and there is also greater aluminum and phosphorus in winter and summer.The release strength.