| This paper mainly studies the transport and transformation behavior of heavy metal cadmium in sediment and its pollution characteristics in sediment medium in the plain flood detention reservoir area where surface water and groundwater are closely related.Heavy metal cadmium can not be degraded when entering the environment,but will accumulate and cause serious harm to crops and other plants and human beings.In the Shifosi Reservoir,there are two water sources,i.e.the water supply source of Shenyang agricultural high tech Industrial Zone and the water source of Huangjia of Shenyang No.7 water plant.The water source takes water from the river as the water supply mode,so heavy metal cadmium may be dangerous with the infiltration of surface water Therefore,it is of great significance to study the transport and transformation behavior of heavy metal cadmium in sediment and its pollution characteristics in sediment medium for the prevention and control of heavy metal cadmium pollution.As the Huangjia water source in the reservoir area is the main water supply source in the new area of Shenbei,this study is also of great practical significance to ensure the safety of water supply in the new area of Shenbei.At the same time,it has important theoretical significance to expand the research field of heavy metal cadmium migration and transformation in sediment.The spatial distribution of heavy metal cadmium in the reservoir area is that the eastern part is higher than the western part,the northern part is higher than the southern part,and the low floodplain is higher than the high floodplain.The migration of cadmium in vertical direction is greater than that in horizontal direction,which shows vertical accumulation.In terms of lithology,the content of heavy metal cadmium in silty clay is higher than that in silty fine sand.Through the correlation analysis of heavy metal cadmium and various factors,the content of heavy metal cadmium in the deep sediment has a significant positive correlation with the content of iron.The negative correlation between the content of heavy metal cadmium and the p H value indicates that the alkaline soil is easier to absorb heavy metal cadmium,and heavy metal cadmium is easier to migrate and transform in the acid condition and is not easy to be fixed.The negative correlation between heavy metal cadmium and water content of sediment indicates that the higher the water content of sediment medium is,the lower the content of heavy metal cadmium is.The adsorbed heavy metal cadmium may be desorbed and migrated with the existing pore water.The more the proportion of solid components is,the easier it is to adsorb and fix heavy metal cadmium.It may also be that the content of dissolved cadmium is small,so the higher the water content,the less the content of heavy metal cadmium in the sediment.According to the ecological hazard assessment of heavy metal cadmium and the evaluation method of Nemero index,the comprehensive pollution degree of spatial distribution of heavy metal cadmium sediment in the reservoir area is light pollution,the pollution grade is grade 3,and the pollution value exceeds the initial pollution value.The pollution of heavy metal cadmium is the most serious at the depth of160cm to 200cm in point C,the pollution degree is medium pollution,and the potential ecological harm degree is also moderate.The results show that the equilibrium adsorption capacity of each porous medium is25℃silty clay>15℃silty clay>25℃Silty Sand>15℃Silty Sand>25℃fine sand>15℃fine sand,and the corresponding maximum adsorption capacity respectively is 93.53mg/kg、91.71mg/kg、81.82mg/kg、77.5mg/kg、53.8mg/kg、47.5mg/kg.The higher the temperature is,the larger the constant value of quasi second-order adsorption rate is,and the shorter the time for heavy metal cadmium to reach adsorption equilibrium in the sediment medium is.The desorption rate of heavy metal cadmium in the sediment of the reservoir area:25℃fine sand>15℃fine sand>25℃Silty Sand>15℃Silty Sand>25℃silty clay>15℃silty clay,the desorption rate has a negative correlation with the specific surface area of porous media.According to the breakthrough curve of bromine ion,the dispersion coefficient of porous silty clay is 0.0033m~2/d,the dispersion is 0.017m,and the effective porosity is 24.6%.It can provide parameter support for later scholars to study the transport simulation of heavy metal cadmium in sediment in Shifosi Reservoir area.The breakthrough curve of heavy metal cadmium in porous medium silty clay of sediment shows asymmetry and obvious tailing phenomenon,which indicates that there is dynamic adsorption and desorption of cadmium in the process of migration.Through the isotherm adsorption test of heavy metal cadmium in the sediment medium of the reservoir area under different conditions,the large and small redox potential in the chemical properties of the sediment medium of the reservoir area will reduce the p H value,increase the mobility of heavy metal cadmium,increase the ionic strength to inhibit the migration of heavy metal cadmium,and promote the migration of heavy metal cadmium in the presence of colloid.Under the change of redox status,the adsorption capacity of heavy metal cadmium was as follows:silty clay>reducing soil>oxidizing soil.With the increase of ionic strength,the adsorption capacity of heavy metal cadmium in the sediment medium decreases,and the increase of ionic strength also leads to the increase of the interaction force between the ions,and the increase of free binding ions in the solution,which accelerates the transport of heavy metal cadmium.In the presence of colloid,silica gel has a large number of negative charges,and colloid has a huge surface area and surface energy,which can produce electrostatic adsorption or specific adsorption of heavy metal cadmium,so that the heavy metal cadmium adsorbed in the sediment can be adsorbed into the colloid in the form of surface complexation,thus reducing the adsorption of heavy metal cadmium in the sediment.According to the 16S amplification sequence of microorganisms,the top 10 microbial species selected in this experiment are Bacillus＿aryabhattai,Clostridium＿disporicum,Acidobacteria＿bacterium＿RBG＿16＿70＿10,Brevundimonas＿bullata,Arthrobacter＿globiformis,Burkholderiales＿bacterium＿X4,Ralstoniainsidiosa,Bacteroides＿vulgatus,Clostridium＿bowma nii and Deltaproteobacteria＿bacterium＿CSP1-8,which are not known to have strong cadmium resistance Microbial species.According to the comparison between the distribution characteristics of Cd content in C and D points and the distribution characteristics of microbial species,the dominant microbial species measured have no significant correlation with them.Through the enrichment experiment of heavy metal cadmium in the roots of two kinds of aquatic plants,it is found that Typha has a little more enrichment effect on heavy metal cadmium than reed,which can reach 1.25mg/kg.The results show that reed and cattail in the study area have a strong enrichment effect on the heavy metal cadmium in the sediment,which can be used as the plant selection for pollution control and remediation of heavy metal cadmium.It shows that plants are also the main destination of heavy metal cadmium migration.It is suggested to plant reed and cattail to enrich the heavy metal cadmium in the sediment,so as to reduce the harm of heavy metal cadmium to the reservoir environment.Moreover,the purpose of remediation of heavy metal cadmium pollution in the reservoir area can be achieved by removing plants regularly. |
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