Study On Pollution Characteristics And Nitrogen And Phosphorus Release Of Sediments And Overlying Water In Zhanrze Rervoir

Sediments are habitats for flora and fauna in lakes and reservoirs and their watersheds,as well as important storage places for nutrients,heavy metals and other pollutants.The study found that the increase of nutrients such as nitrogen and phosphorus in water is the leading factor leading to eutrophication of lakes and reservoirs.The continuous input and long-term accumulation of nitrogen and phosphorus,the sediments of lakes and reservoirs gradually affect the water quality in the form of endogenous pollution.Under the influence of the environmental conditions of the water body,these endogenous loads will accumulate in the sediment by sedimentation or particle adsorption,and will be released by the water body by resuspension,which seriously affects the quality of the overlying water body in the lake reservoir.In this study,the Zhangze Reservoir was taken as the research object.The spatial and temporal variation characteristics of nitrogen and phosphorus nutrients in sediments and overlying water were studied by on-site sampling,indoor testing and experimental simulation.The pollution of nitrogen and phosphorus nutrients in reservoir sediments was studied.The situation was evaluated.The law of nitrogen and phosphorus release from sediments was studied and analyzed.The research results are of great significance for controlling the water pollution in the lake reservoir.The main research work and results of the thesis are as follows:(1)Temporal and spatial distribution of physical and chemical indicators and nutrient salt indexes of water bodies In October 2017-2018,the sampling and monitoring of overlying water at 16 sampling points of Zhangze Reservoir were carried out to analyze the spatial and temporal distribution of physical and chemical indicators and nutrient indicators of reservoir water.The results show that the seasonal distribution characteristics of physical and chemical indicators in the reservoir are characterized by water temperature,high pH in spring,summer and autumn,low in winter,low transparency and dissolved oxygen in spring,summer and autumn,and high in winter.The total nitrogen,total phosphorus and ammonia nitrogen in the nutrient index of the reservoir are characterized by the gradual decrease of the reservoir water into the water in front of the dam;The COD contour change is characterized by high pollution in the area before the reservoir dam in the fall.In spring,summer and winter,the concentration from the center of the reservoir to the surrounding waters gradually increases;In the spring,chlorophyll gradually decreased from the center of the reservoir to the surrounding waters,and the summer,autumn and winter showed a gradual decrease from the reservoir inflow to the water in front of the dam.(2)Study on pollution characteristics of nutrients and heavy metals in sedimentsThe pollution distribution of nutrients and heavy metal elements in the surface sediments of the Zhangze Reservoir was analyzed.The results showed that total nitrogen,ammonia nitrogen,total phosphorus and heavy metals(Cu,Pb,Zn,Cd,Hg,As)in the surface sediments.The characteristics of spatial distribution characteristics are consistent,and the pollutions in the dam front and the tail area are serious,and the pollution in the central area is light.The results show that the pollution pollution index(FF)of the sediment pollution layer is>2.0,and the pollution state is heavy pollution.The evaluation of heavy metals shows that Hg and Cd contribute the most to the potential ecological risk index,reaching 52.06%and 45.43%.(3)Laboratory simulation study on sediment-overlying water,nitrogen and phosphorus releaseThrough the indoor sediment-overwater release simulation test,the environmental conditions such as temperature,pH and dissolved oxygen were controlled to analyze the law of nitrogen and phosphorus nutrient release intensity in surface sediments.It was found that with the increase of temperature level,TN,TP,The release intensity of NH4+-N increased significantly.With the increase of pH level,the release rate of TN,TP and NH4+-N decreased first and then increased.With the increase of DO level,the release rate of TN,TP and NH4+-N decreased..The relationship between the release intensity of nitrogen and phosphorus in sediments and the relationship between temperature,pH and dissolved oxygen was compared and the best fitting curves of NH4+-N,TN and TP release strength and dissolved oxygen environment factors were obtained.It is a cubic function;the NH4+-N and pH optimal fitting curve is a quadratic function,and the TN,TP and pH optimal fitting curves are cubic functions;the optimal distribution the release intensity and temperature of NH4+-N,TP and TN in the sediment is a quadratic function.(4)Mathematical model establishment and release estimation of sediment-overlying water,nitrogen and phosphorus releaseThe orthogonal experiment was designed to analyze the combined effects of multiple factors on the release of nitrogen and phosphorus in sediments.The regression equations of total nitrogen and total phosphorus release rate and temperature,pH and dissolved oxygen environment variables were established by multiple linear regression method.RTN=3.089*T+21.027*pH+5.770*DO-25.970,RTP=0.753*T-13.712*pH-3.511*DO+192.262,the significance test was carried out,and three environmental factors such as temperature,pH and dissolved oxygen were applied to the reservoir deposition.The release of nitrogen and phosphorus release have significant effects.Within the range of values specified by each test factor,the significant order of release of TN and TP in sediments is pH>water temperature(T)>dissolved oxygen(DO).The release rate mathematical model is used to estimate the annual total nitrogen release of sediments in the reservoir water body is 303.125t,and the total phosphorus release is 103.943t.