Study On Release Of Nitrogen And Phosphorus In The Sediment Of Yanming Lake And Main Environmental Impact Factors

With the acceleration of urbanization,excessive discharge of pollutants into lakes has made lake water eutrophication problems increasingly serious.Especially urban artificial lakes have the characteristics of closed environment,poor mobility and shallow water depth,and the water environment is more vulnerable to pollution Even if the external pollution is controlled,the internal pollution caused by the release of sediment cannot be ignored.This study takes Yanming Lake 2#Lake in Xi'an as the research object,studies the overlying water and sediments of the lake,analyzes the pollution characteristics and distribution rules of nutrients in the water body and sediments;through indoor simulation experiments,the interfacial nitrogen and phosphorus are studied The variation law of release and the influence of environmental factors on the release of nitro gen and phosphorus;based on the response surface method,construct a regression model of nitrogen and phosphorus release,predict the most unfavorable release conditions of sediment,and estimate the annual release of nitrogen and phosphorus in the sediments of Yanming Lake.The main research contents and results are as follows:?1?The monitoring results of the water body and sediment of Yanming Lake from February to December 2019 show that the water temperature and permanganate index are high in summer and autumn,low in spring and winter,and the dissolved oxygen and pH are low in summer and high in winter.Seasonal distribution characteristics;TN content in overlying water belongs to category IV water,TP content belongs to category III^IV water,TN and TP content in interstitial water exceeds category V of surface water environmental quality standards,TN pollution is not significantly different in space,TP pollution shows a trend of high in the middle and low in both sides.The comprehensive pollution assessment result of sediments is moderate,and the organic pollution assessment is relatively clean-still clean;the pollution degree of the two assessment methods is basically the same in space,both of which indicate that the pollution of M2 is the most serious,followed by the pollution of M3,M1 and M6 The least degree.?2?The TN,NH₄⁺-N,TP and PO₄^3--P exchange fluxes of the lake sediment-overlying water interface were estimated through indoor simulation experiments.The results showed that the fluxes of the four nutrients were the largest in summer and autumn,and the temperature dropped in winter After icing,it is not conducive to the release of nutrients,and the exchange flux is reduced;spatially,the nitrogen flux is larger in the center of the lake,the inlet and outlet are smaller,and the phosphorus flux distribution is opposite.According to the positive and negative of the flux,except that NH₄⁺-N in the sediment is"sink"for part of the time,the three nutrients TN,TP and PO₄^3--P in the sediment all appear as"source"in the four seasons".At the same time,it is estimated that the contribution rate of nitrogen and phosphorus release from the sediment-overlying water interface to nutrients in the water body are:TN potential contribution rate is 3.9⁹.11%,NH₄⁺-N potential contribution rate is-5.31⁶.9%,TP potential The contribution rate is 2.48⁹.72%,the potential contribution rate of PO₄^3--P is 3.65⁸.7%.?3?Taking the overlying water and sediments of Yanming Lake as the research object,the effects of changes of single environmental factors on the release of nitro gen and phosphorus in sediments were studied through simulation experiments.The results showed that the TN,NH₄⁺-N,TP and PO₄^3--P Fluxes increase with increasing temperature and decrease with increasing dissolved oxygen concentration.The pH is the smallest under neutral conditions,the TN and NH₄⁺-N fluxes are the largest under acidic conditions,and TP and PO₄^3--P flux The amount is maximum under alkaline conditions.Curve fitting is performed on the relationship between environmental factors and nitrogen and phosphorus fluxes,and it is concluded that the types of optimal fitting curves between different nutrient fluxes and environmental factors are not exactly the same.?4?Based on the response surface method,the quadratic polynomial regression mode l of temperature,dissolved oxygen,pH,and nitrogen and phosphorus(TN,NH₄⁺-N,TP,and PO₄^3--P)fluxes is obtained,and the contour plot and response surface plot are drawn,From the analysis of interactions:temperature and pH interactions have a significant impact on TN flux;temperature and dissolved oxygen interactions,temperature and pH interactions on NH₄⁺-N Flux has a significant effect;temperature and dissolved oxygen interactions have a significant impact on TP flux;the interaction between te mperature and dissolved oxygen has a significant effect on the PO₄^3--P flux.And the most unfavorable release conditions of lake sediments are optimized:T=10?,DO=7.87 mg·L^-1,pH=7.13,and the nutrient exchange flux takes the minimum value.Combining the obtained regression model with the actual environmental conditions of the lake to estimate the amount of nitrogen and phosphorus released from the lake,the TN release from Yanming Lake sediment is 1.954 t·a^-1,the NH₄⁺-N release is 0.739 t·a^-1,and the TP release It is 0.223 t·a^-1,and the release amount of PO₄^3--P is0.068 t·a^-1.