| As the most complete urban lake and wetland in Yinchuan City,Yuehai has been undergoing a large amount of domestic sewage discharge and the use of pesticides and fertilizers in the suburbs since the development of the western region and the progress of urbanization.In recent years,with the development of the autonomous region ecological strategy,the issue of wetland environment improvement and restoration has received widespread attention.Among them,a series of measures such as blocking and removal of external pollution(point source and point source)were effectively controlled.however,the secondary release of pollution from the sediment has not yet attracted attention,so the pollution problem is difficult to eradicate.Taking into account factors such as water depth,reed distribution,and spatial distance,14 sampling points were evenly arranged in the sea reading,and the spatial and temporal distribution characteristics of the water quality conditions of the overlying and interstitial waters and the physical and chemical properties of the sediment were studied to obtain the pollutant indicators in each medium There is a huge concentration difference,indicating that the risk of secondary release of sediment pollutants has been formed.Through the indoor sediment release simulation experiments,the effects of layered,undisturbed sediment,different levels of pollution on the release of sediment pollutants,and environmental factors on the release of sediment pollutants were explored.Lake wetland water quality monitoring and sediment internal pollution control provide theoretical basis and data support.The main research results are as follows:(1)The water quality indicators of the overlying water and interstitial water in the Yuehai are obviously different in time and space distribution.Among them,the concentration of the water quality indicators of the overlying water is temporally distributed:August is the lowest,November is the second,and August is the highest;the spatial distribution is:The water quality of the replenishment and deep water areas is better,followed by the drain and shallow water areas,and the reed area is the worst.The concentration of various water quality indicators of interstitial water is highest in May,followed by August,and relatively low in November;the spatial distribution of various water quality indicators of interstitial water is higher in the reed area and shallow water area,followed by the drainage outlet,deep water area and replenishment The mouth is low.Comparing the water quality index concentrations of overlying water and interstitial water at 14 sampling points,it is found that the water quality indicators of interstitial water in sea reading are significantly higher than the overlying water at the corresponding point.There must be a risk of migration and transformation of polluting elements between sediments.(2)The impact of indoor simulated sediment release on overlying water shows that:? Under natural conditions,the migration and transformation of various pollution indicators of sediment in a short period of time are relatively volatile.Among them,the NH3-N indicators are all released,and the 0-2 cm surface layer releases the most strongly,but the 0-15 cm undisturbed NH3-N cumulative release is higher,indicating that the migration and transformation of pollutants between the sediment and water are not Limited to the surface.The 0-2 cm layer of the TP index layer was released.The other layers and the undisturbed sediment were released in the first 12 h,and then in the adsorption state.In addition to the CODMn index,except for the surface layer 0-2 cm,which is highly volatile and has been released too much,the other layers and the undisturbed sediment have changed from release to adsorption after 9 hours.? There are differences in the release period,cumulative release amount and release rate of sediment pollutants at different pollution levels,which indicates that the release capacity of sediment pollutants is related to the concentration of sediment pollutants,but only if there is a large enough concentration difference,will the release amount and There are significant differences in release rates.When the concentration of pollutants between sediment and water reaches a dynamic equilibrium,that is,the threshold for pollutant migration and transformation,the release differences caused by sediments with different pollution levels will disappear.(3)Research on the influencing factors of indoor simulated sediment release shows that temperature,pH and overlying water concentration will all affect the cumulative release and release rate of sediment in Ningxia Yuehai,but the degree of influence exists under different conditions.? Under the condition that the overlying water is acidic,the release amount of NH3-N and CODMn gradually increases with the increase of temperature;under the overlying water alkaline condition,the temperature is 15?,the maximum amount of NH3-N is released,and the temperature Too high or too low,the amount of NH3-N released is low.High temperature can inhibit the release of TP and promote the release of CODMn.At low temperature,when the pH of the overlying water is neutral,the release amount of NH3-N and CODMn is more,and there is no significant change in the amount of TP.At high temperature,the pH of the overlying water is neutral,which is more conducive to NH3-N.And TP release,while CODMn is more suitable to release under alkaline conditions.? The threshold of NH3-N migration and conversion between the seabed mud and water does not exceed 0.5 mg/L.The initial concentration of TP in the overlying water is controlled to 0.3 mg/L,and the sediment is converted from release to adsorption process,which indicates that the threshold of TP migration and conversion between the sediment and water does not exceed 0.3 mg/L.The initial concentration of CODMn in the overlying water is controlled to 10mg/L,the sediment is converted from release to adsorption process,and the adsorption rate reaches 0.68,which indicates that the CODMn migration and conversion threshold between the sediment and water is much lower than 10 mg/L. |
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