Risk Analysis And Restoration Strategy Of Mercury Pollution In Degraded Grassland Of Songnen Grassland

Mercury is a wide range of heavy metal elements in nature.It has the characteristics of high biological enrichment,concealment,persistence and easy migration.Different forms of mercury can be discharged into the atmosphere to carry out the global cycle of mercury,which will return to the surface through dry and wet deposition,enter the soil and grassland ecosystems,and complete the biogeochemical cycle of various scales.In grassland ecosystem,typical plants as producers are the material basis of grassland ecosystem food web.After Mercury enters the grassland ecosystem,through grassland management such as grazing and mowing,through the bioaccumulation effect or biomagnification process of the food chain,it seriously threatens the health of high trophic organisms.Therefore,it is very important to evaluate the mercury pollution risk of the "soil vegetation" system of grazing grassland and formulate regional management strategies and prevention and control measures.The sample plot of the study is located in Songnen grassland,beidianzi grassland,YaoJingzi village,Changling County,Jilin Province.According to the current situation of grassland soil environment and grassland degradation,four typical vegetation soils in typical pasture sites are selected as the research objects,including sheep grassland(not degraded),alkali grass alkali Artemisia land(moderately degraded),light alkali spot land(severely degraded)and grassland protective forest land(artificial forest).Collect samples of soil and typical plants in the sample plot,and use LUMEX RA-915+mercury meter to determine the total mercury content in the soil profile layer;Use HI98185 portable waterproof pH meter to measure the pH value of soil;The potential ecological risk index(EI)method was used to evaluate the potential ecological risk of mercury in the above grassland soil vegetation system;The health risk evaluation model was used to evaluate its health risk.Furthermore,the management strategy of gradually restoring productivity of grassland soil vegetation system was put forward.The relationship of total mercury content in soil(0～100cm)of typical vegetation sample plot is as follows:light alkali spot land>alkali grass alkali Artemisia land>sheep grassland>forest land,The corresponding mean values are:10.80±1.07ng/g、7.15 ± 1.03 ng/g、6.55 ± 0.94 ng/g、6.04±1.12 ng/g.The relationship of mercury content in the whole plant of typical vegetation is:alkali Artemisia selengensis>dogtail grass>leymus chinensis.The corresponding mean values are:3.71±1.01ng/g、3.50±1.01ng/g、3.50±1.01ng/g.The enrichment ability of alkali grass and alkali Artemisia to soil mercury is the strongest,and there is little difference between Leymus chinensis and Dogtail grass.The analysis of grassland vegetation degradation shows that the degradation of typical vegetation in Songnen grassland will increase the total mercury content accumulated in the soil.The distribution characteristics of mercury content in the soil of forage plot are as follows:The characteristics of spatial vertical distribution are as follows:except for forest land,the mercury content of other three forage plots in 0-20cm layer(significant difference)is significantly higher than that in less than 20cm layer;The characteristics of spatial horizontal distribution are as follows:most of the high mercury areas are distributed in the light alkali spot sample land and the alkali grass alkali Artemisia light alkali spot transition zone in the south of the study area,and sheep grassland and forest land are generally in the low mercury area.The characteristics of seasonal distribution are:summer>spring>autumn.Soil physical and chemical properties and environmental conditions will have a certain impact on soil mercury content.The results showed that in the same season,the soil pH value of light alkali spot was the highest and that of forest land was the lowest.In the soil profile,all sampling points show a trend that the pH value first increases and then decreases from the surface to the deep layer.For a single vegetation soil.the soil pH value is the highest in autumn and the lowest in summer in different seasons.The calculation results of potential ecological risk show that the range of potential ecological risk index of soil surface mercury in the sample plot is 30≤EI(average value)<80.and the average content of mercury in the soil surface is12.23±2.25ng/g.The soil mercury El average of forest land and sheep grassland is less than 40.and the potential ecological risk is low I:The range of ecological risk index of soil surface mercury in alkali grass alkali Artemisia land and light alkali spot land is 40 ≤EI(average value)<80 and the potential ecological risk is medium Ⅱ.In general,there is a potential risk of mercury pollution in the sample soil.The more degraded grassland is.the stronger the potential ecological risk of mercury pollution is.The results of health risk calculation showed that among the three exposure routes of soil mercury in pasture,oral intake was the main intake route:In addition to respiratory intake,the mercury intake of children under the other two intake routes is much higher than that of adults;The total hazard index hi of three exposure routes of mercury in pasture soil to adults and children is less than 1,indicating that the health risk of mercury pollution is at an acceptable level.According to the experimental results,this study puts forward a comprehensive restoration strategy and scheme of degraded grassland,that is,using adaptive management strategy to effectively manage degraded grassland.The micro ecological restoration project is used to improve the hardening of soil and repair the degraded grassland by using the principles of soil deep tillage,subsoiling technology,application of soil improvement conditioner and plant root restoration.