Phosphorus Adsorption And Release Characteristics And Coverage Control Of Small Shallow Lakes In Urban Areas

Kongmu Lake is a small urban shallow lake located next to a university in Nanchang City,Jiangxi Province.It is affected by the sewage discharge,animal and plant residues and rainwater runoff of the campus and surrounding residents.The eutrophication of the water is relatively serious.In this paper,the small shallow lake in the natural city of Kongmu Lake is taken as the research object.The variation patterns of phosphorus forms and contents in sediments of Kongmu Lake were studied.The spatial distribution characteristics and correlation of different forms of phosphorus in sediments were analyzed.Combined with indoor simulation experiments,the effects of sediment on the adsorption and release of phosphorus and the adsorption and release behavior of phosphorus in sediments under different environmental conditions were studied.Simultaneously inhibiting the release of phosphorus from sediments by three kinds of covering materials,kaolin,zeolite and calcite.On the basis of this,the effects of calcite on in-situ coverage control under different environmental conditions were studied.The main conclusions are as follows:?1?The TP content in the sediments of Kongmu Lake is 2338.63-2954.98 mg/kg,and its main form is Fe-P.The order of the content of each sampling point TP is:L8>L2>L1>L5>L7>L3>L4>L6>L9.The order of phosphorus content in sediments from high to low is:Fe-P>De-P>Ca-P>OP>Al-P>Oc-P>Ex-P.The horizontal distribution characteristics of phosphorus in sediments showed that the changes of phosphorus Fe-P,De-P,Ca-P and OP in the same monitoring site had the same change,and their content was Fe-P>De-P>Ca-P>OP.There is a certain difference in the change of phosphorus content in the same form at different monitoring points.The vertical distribution characteristics of sediment phosphorus in sediments indicate that the surface enrichment phenomenon of sediment phosphorus reveals that endogenous pollution is serious.On the one hand,it is greatly affected by artificial disturbance.The main factor is the input of a large amount of exogenous phosphorus.On the other hand,it may be related to the characteristics of sediments.Correlation analysis showed that there was a significant positive correlation between TP content and Fe-P content in sediments,indicating that the accumulation of TP in sediments was mainly due to the increase of Fe-P content.?2?The kinetic adsorption of phosphorus on the surface sediments of Kongmu Lake accords with the Lagergren quasi-secondary adsorption kinetics equation.The adsorption of phosphorus in surface sediments mainly occurs in 0-3 h,the fast adsorption process occurs in0-1 h,and the slow adsorption phase within 1-3 h.At low concentration,desorption behavior exists at all three sampling points,and gradually enters the adsorption stage with the increase of phosphorus concentration.Under high concentration conditions,the adsorption isotherm of phosphorus in surface sediments accords with the Langmuir model,and the maximum adsorption capacity(Q_max)of phosphorus is 555.56-625.00 mg/kg.The adsorption/desorption equilibrium mass concentration?EPC₀?of the surface sediments at each sampling point is0.129-0.177 mg/L,which is smaller than the phosphate content in the overlying water.It is characterized by phosphorus“sink”,which can be preliminarily determined that the sedimentation of the Kongmu Lake is less risky in the short-term release of water,and it has a buffering effect on the phosphorus in the overlying water.Under acidic or neutral conditions,the adsorption of phosphorus by surface sediments is obvious.Under alkaline conditions,the adsorption of phosphorus by surface sediments is not obvious,and the higher the pH value,the smaller the adsorption amount.?3?The amount of phosphorus released from the sediment increased first and then decreased with time,and reached the maximum on the 7th day,and the maximum concentration of phosphorus released from the sediment was 0.380 mg/L.The effect of pH on the release of phosphorus from sediments is obvious.Under alkaline conditions,the release of phosphorus from sediments is large,and the release of phosphorus from sediments under acidic or neutral environmental conditions is small.The temperature has a great influence on the release of phosphorus from sediments.The higher the temperature,the larger the TP content of the overlying water and the greater the release of phosphorus from the sediments.The release of phosphorus from sediments was inhibited under low temperature conditions.The TP content of the overlying water was the lowest,and the release of phosphorus from the sediments was also the smallest.In general,an increase in temperature can increase the amount of phosphorus released from the sediments.Disturbance is a physical factor affecting the release of phosphorus from sediments in shallow lakes.As the disturbance intensity increases,the TP content of the overlying water also increases.However,the continuous disturbance can not lead to the continuous release of phosphorus in the sediment.The resuspended particles can adsorb the phosphorus in the overlying water,which cause flocculation and precipitation into the sediment.As the disturbance time increases,the effect of the phosphorus release from the sediment caused by the disturbance is weakened.?4?Through the indoor simulated coverage experiment,the three covering materials have a good control effect on the phosphorus release from the sediment,and the calcite>kaolin>zeolite>blank group,the best coverage of the sediment release phosphorus release is the calcite group.After the 17th day,the TP content of the overlying water was 0.136mg/L,and the inhibition rate of phosphorus release from the calcite-covered sediment was77.67%.The best material size of calcite for the control of phosphorus in the sediments of Kongmu Lake is 500 mesh.After the 17th day,the TP content in the sediment-overlying water is 0.021 mg/L,and the inhibition rate of phosphorus release from calcite-covered sediments.64.91%.The best coverage thickness of calcite for the phosphorus control of sediments in Kongmu Lake is 3-5 cm.After the 17th day,the TP content of the overlying water was 0.136mg/L and 0.030 mg/L,respectively,and the inhibition rates were 77.67%and 95.02%,respectively.The higher the temperature of the overlying water,the smaller the release of phosphorus from the calcite-covered sediment,and the better the control effect on the release of phosphorus from the sediment.After the 17th day,the TP content in the sediment-superfluid water of the calcite coating at 5°C,25°C,and 35°C was 0.017 mg/L,0.051 mg/L,and 0.019mg/L,respectively.The low-temperature or high-temperature environmental conditions of the overlying water have a good inhibitory effect on the release of phosphorus from the sediment.The greater the disturbance intensity,the greater the release of phosphorus from the calcite-covered sediments and the corresponding reduction in the release of phosphorus from the calcite-covered sediments.Under the conditions of overlying water disturbance intensity 50r/min,150 r/min and 250 r/min,the inhibition rates were 74.30%,72.63%and 69.24%,respectively.It indicates that the overlying water disturbance has a certain effect on the release of phosphorus from calcite-covered sediments.But in the short term,it can inhibit the release of endogenous phosphorus.