Research On Influencing Factors Of Internal Phosphorus Release Flux In A Reservoir In Siping Area

Xiasantai reservoir is a medium-sized reservoir for flood control,urban water supply and fish farming.Its average annual water supply accounts for more than 20% of the total water supply in the urban area.It has played an important role in developing and prospering siping’s economy and improving the quality of life of siping people.With the continuous increase of water pollution control in recent years,the water quality index of the reservoir is generally good except for total phosphorus.Under the condition that the exogenous pollution is gradually controlled,the internal phosphorus pollutants released by sediments in the overlying water become the main reason for the high concentration of total phosphorus in the water.In order to reduce the level of nutrient phosphorus in the reservoir water and improve the water quality of the reservoir area,based on the change rule of typical water quality indexes,the spatio-temporal change rule of different forms of phosphorus in the overlying water was analyzed.The SMT continuous extraction method was used to analyze the occurrence form of phosphorus in the sediment and its horizontal and vertical distribution characteristics.To study the influence of main environmental factors on the release of phosphorus in sediment and overburden water,and to study the release intensity,release rate and release flux of internal phosphorus in different seasons.The main research contents are as follows:In this paper,nine monitoring points were set up in the reservoir area,and the surface water,overlying water and sediment of each sampling point were collected and measured in different seasons.There were certain differences in p H,DO,permanganate index,transparency and algal density distribution at different points in the surface water of the reservoir.The concentration of TP and TDP in overlying water was higher in summer and lower in spring,while the concentration of SRP was higher in autumn and lower in summer.TP mainly exists in the form of IP in sediments,and THE main existence form of IP is CA-P,which is related to the topography,formation lithology and hydrogeology around the reservoir.In terms of the horizontal distribution of all forms of phosphorus in the overlying water and sediment,the concentrations of phosphorus were higher near the water refill outlet on the bank of the reservoir,the surrounding residential areas,the central area of the reservoir and the deeper water level.The phosphorus content in the bottom sediments is higher than that in the surface sediments,indicating that the input of exogenous phosphorus pollution has been effectively controlled in recent years.The horizontal distribution of nutrient phosphorus in the overlying water is similar to that of various phosphorus forms in the sediments at the monitoring points with higher concentration,and the phosphorus in the overlying water largely comes from the release of endogenous phosphorus.Temperature has a significant effect on the release of endogenous phosphorus in sediments.Low temperature inhibits the release of endogenous phosphorus,while rising temperature promotes the release of endogenous phosphorus.The higher the temperature,the greater the release of endogenous phosphorus.When p H of water was neutral,the release of phosphorus in sediments was the lowest,and the release increased under alkaline or acidic conditions.Alkaline conditions were more conducive to the release of endogenous phosphorus.Anaerobic promotes the release of endogenous phosphorus,while aerobic inhibits the release of phosphorus in sediments.The greater the content of dissolved oxygen,the less the release of endogenous phosphorus.Disturbance can promote the release of phosphorus in sediments in a short time.The internal phosphorus release fluxes in different seasons were 0.185 t,0.492 t and0.140 t,respectively.The release flux of endogenous phosphorus is the highest in summer,and the release flux at some monitoring points is negative in autumn,indicating that the sediment in the reservoir absorbs phosphorus from the overlying water as the "sink" of endogenous phosphorus in autumn.Combined with the actual situation of the reservoir,it is suggested that the treatment measures of artificial dredging,ecological restoration and aeration are combined.