Heavy Metals Spatial And Temporal Distribution Characteristics And Reclamation Suitability In Typical Coal Mining Areas With High Groundwater Level

Heavy metals pollution not only destroys the environment,but also poses a serious threat to human health in coal mining subsidence areas with high phreatic levels in China.It is very necessary to grasp the temporal and spatial distribution characteristics of soil heavy metals under different reclamation modes in coal mining areas.It has great significance for guiding the future reclamation and ecological restoration of mining areas.The disserarion took the soil,sediment,water and plant in coal mining subsidence reclamation areas in Peixian as the research objects.And the experimental analysis,Kendall tau-b correlation analysis,principal component analysis(PCA),hierarchical cluster analysis(HCA)and other methods was applied.The temporal and spatial distribution characteristics of heavy metals in different reclamation modes and utilization methods were studied.This study explored the response laws of microorganisms to reclamation activities.In addition,a new method for evaluating the suitability of land-use types and reclamation methods in subsidence areas considering pre-subsidence was proposed.The main conclusions were as follows.(1)Based on the heavy metal data of 332 soil samples from Pei city in the 2014National Soil Survey,it revealed the distribution characteristics of 7 heavy metals including Cd,Pb,Cr,Cu,Zn,Hg,and As.Statistical methods such as the cumulative index method and Kendall tau-b correlation analysis were used to explore the sources of heavy metals.The content of each heavy metal in the soil of Peixian City did not exceed the Soil Environmental Quality in the Agricultural Land Soil Contamination Risk Management Control Standards(GB15618-2018),and the content of Hg,Cd and Cu is higher than the background value of Jiangsu Province.I_georesults showed that Pb,Cr,Cu,Zn and As content is at the clean level,while Cd and Hg are at the uncontaminated to moderately contaminated level.Hg pollution is more serious in the coal mine subsidence area.The results showed that the combination of Kendall's tau-b correlation analysis,HCA,PCA,and geostatistical analyses could be used to identify potential sources for these potentially toxic elements.Cr,Zn,Cu,Pb,Cd,and As most likely shared a common source.Possible sources of contamination could be coal mining activities,water transportation,or livestock manure.The highest Hg level was most likely due to human mining activities.Of all of the heavy metals contaminants we examined,Pb was the only element that posed a non-carcinogenic health risk to children,even if the levels were not high enough to be a risk to the adults in our study area.Considering the excessive heavy metals in the soil,the health risk assessment and the scope of the subsidence,it can be found that there was a certain risk of heavy metal pollution in the coal mining subsidence area(non-pumped area and subsidence water area)in Peixian city.(2)171 soil samples and 57 vegetation samples from 19 plots were selected from coal gangue filling reclamation areas,land levelling reclamation areas and hydraulic dredge pump reclamation areas.Based on their basic physical and chemical properties and heavy metal content,Spatial and temporal distribution of soil heavy metals were compared and analyzed three types of reclamation areas.The results show that there was the lowest total heavy metal content,over-standard rate and pollution degree of the soil in land levelling reclamation areas.And the pollution degree of heavy metals was relatively higher in coal gangue filling reclamation areas.There was no uniform law of distribution of heavy metals and other physical and chemical properties in the soil along the profile in all the three areas.There was no much difference of heavy metals content between land levelling reclamation soils and the control farmland soils,indicating that the disturbance of reclamation was minimal.And Zn,Cu,As were mainly derived from the application of chemical fertilizers and pesticides,while Cd,Cr,Hg,and Pb were mainly derived from coal mining activities,atmospheric deposition in land levelling reclamation areas.The common source of Cd,Pb,Cr,Cu,Zn and As was the filling mud,and Hg mainly came from mining activities in hydraulic dredge pump reclamation areas.In general,the land leveling technology could be popularized and applied in the reclamation of subsided areas in the future,and the lake mud filling technology could also be considered in areas with rich lake mud resources.(3)36 samples of sediment,overlying water and aquatic plants were collected from 12 samples in Anguo wetland,fish farming area,and fishing-light complementary area,and the distribution characteristics of heavy metals were systematically analyzed.The heavy metals pollution was anaylized in the Anguo wetland,aquaculture pond,and fishery-solar hybrid project regions based on the statistical methods such as single-factor pollution index method,Nemerow pollution index method,Kendall tau-b correlation analysis and geostatistical analysis method.The results showed that the degrees of heavy metals contamination in the three regions were lower than that in the control region.As a purification wetland,Anguo wetland had a good purification effect on the 50,000 tons of incoming water from the Peixian Development Zone and Longgu Development Zone.Fishery farming can bring certain economic benefits.It was necessary to choose bait and drugs with lower Cu and Zn content in the future.The fishing-light complementary model made full and efficient use of accumulated water resources and land resources in the subsidence area.The development and utilization modes of the three types could bring certain ecological,social and economic benefits.The corresponding development and utilization modes could be selected according to different needs in the future.(4)The effects of land leveling and reclamation activities on soil microbial abundance and community structure were studied based on 16S r RNA sequencing technology.It was found that Shannon diversity index,Chao 1 and Simpson diversity index in most mined samples were lower compared to the unmined soil.Regardless of reclamation ages,Proteobacteria was the most abundant phyla in all seven mine sites.However,at the level of class,order,family,and genus,the dominant populations of soil microorganisms on the reclaimed plots and the control plots were very different.The results of correlation coefficients indicated that Cd,Pb and Cr showed uniformly negative associations with the relative abundance of bacteria Nitrospirae,Planctomycetes,and Acidobacteria,while element Zn was positive with the relative abundance of Nitrospirae,Actinobacteria,Gemmatimonadetes,Planctomycetes,and Acidobacteria.(5)Traditional evaluation methods of land reclamation suitability usually do not consider the impact of coal mining subsidence in the future,and do not evaluate the suitability of reclamation methods and re-use land types at the same time.A collaborative evaluation method of land reclamation methods and re-use land types is proposed,which considers the impact of pre-subsidence.Firstly,the probability integral method is used to predict the surface subsidence of coal mining in 2030,and the suitability evaluation index of pre-subsidence is constructed.Secondly,the suitability evaluation system of reclamation mode and land use type is constructed for the non-waterlogged area and waterlogged area respectively to realize the suitability evaluation.The experimental results show that most of the non-waterlogged areas are suitable to be reclaimed as farmland by mixed pushing and leveling,and the waterlogged areas suitable for wetland development are mainly located in Longdong mining area and Yaoqiao mining area.The resuts are consistent with the existing planning of Peixian city,which verifies the effectiveness of the proposed method for the suitability evaluation of subsidence land reuse.The thesis contains 47 figures,48 tables,and 271 references.