Study On The Mechanism Of Nitrogen And Phosphorus Migration During Sediment Deposition In The Yellow River Diversion Reservoir

Diversion reservoirs have now become one of the main water sources for urban water supply in the middle and lower reaches of the Yellow River,and most of the diversion reservoirs in Shandong Province are at a moderate eutrophication level,which is a huge hidden danger for drinking water safety.The main water source of the Yellow River reservoirs is the Yellow River water,which has a very high content of cement sand,which has an important influence on the migration and transformation process of nitrogen and phosphorus in the Yellow River reservoirs.In order to reduce the sediment entering the reservoir,most of the reservoirs are used to precipitate sediment through front sedimentation canals or sedimentation ponds.It is of great theoretical significance and practical value to study the migration and transformation of nitrogen and phosphorus at the sediment-water interface and sedimentation in the sedimentation area of the reservoir,so as to provide scientific basis for the pollution control management of the reservoir.Based on the special hydrological conditions of the diversion reservoirs,this paper analyzes the water environment of the reservoirs,takes the sediment deposition area of the reservoirs as the key research area,evaluates the water quality of typical diversion reservoirs,studies the water quality and sediment nitrogen and phosphorus of specific diversion reservoirs,and simulates the sediment nitrogen and phosphorus adsorption and release experiments by using statistical analysis The main conclusions of the study are as follows:(1)The main pollutants of typical reservoir water quality and their water quality evaluation methods were identified.The single factor index method,comprehensive pollution index method,Nemero pollution index method and principal component analysis method of water quality evaluation of 15 indexes including total nitrogen and total phosphorus in 6diversion reservoirs in Shandong Province,the results show that: the water quality of diversion reservoirs basically meets the standard,its main pollutant is total nitrogen,and the pollution level is much higher than other pollutants,for this situation,the results obtained prove that the Nemero pollution index method is most suitable The results prove that the method of Nemero pollution index is most suitable for water quality evaluation of this type of reservoir.(2)The sediment nitrogen and phosphorus distribution in Magpie Mountain Reservoir was studied.The results showed that the total nitrogen and total phosphorus contents of sediment were both at low levels,and the sediment nitrogen fugitive forms were mainly leachable nitrogen by weak acid and strong oxidant,while the ion exchange nitrogen and strong alkali leachable nitrogen contents were low.The percentage of organic phosphorus is very low.The spatial distribution of sediment nitrogen and phosphorus was characterized by a clear upward trend of strong oxidant leachable nitrogen,iron-aluminum-bound phosphorus and organic phosphorus in the sediment area,and a relatively uniform spatial distribution of ion-exchange nitrogen,weak acid leachable nitrogen and calcium-bound phosphorus.The results of sediment nutrient evaluation show that sediment does not cause ecotoxic effects.(3)The nitrogen and phosphorus adsorption and release characteristics of the sediments in Magpie Mountain Reservoir were analyzed.Indoor experiments were designed to simulate the sediment nitrogen and phosphorus adsorption process,and the Freundlich model was used to fit the nitrogen adsorption experiment,and the Langmuir model and Freundlich model were used to fit the phosphorus adsorption experiment,and the results showed that: the equilibrium concentration range of nitrogen adsorption and release of sediment at each point was0.5mg/L～2mg/L,and the risk of nitrogen release was generally weak;the equilibrium concentration range of phosphorus adsorption and release of sediment at each point was0～0.1mg/L.The equilibrium concentration range of phosphorus sorption and release of sediment at each point was 0～0.1mg/L,and the risk of phosphorus release in the sediment bar channel was weak,and the reservoir had a certain risk of phosphorus release.In general,sediment mainly adsorbs nitrogen and phosphorus in the water body,and sediment is more difficult to adsorb nitrogen and easier to adsorb phosphorus.