| Near ground is a key area where natural geographical elements,geology,climate,hydrology,soil and biological interactions.Soil is the core part of near ground,and its ecological environment is closely related to human survival and sustainable development.But the continuous accumulation of harmful substances in the soil and near ground has a great impact on the ecological environment and human health.Therefore,it is significance to study the ecological environment near the ground.In the rare earth mining area of Zhuxi basin in western Fujian,under the natural background of soil erosion,there are still human activities such as mining,which caused serious pollution in the process of mass migration of elements.By studied its surrounding ecological environment,this paper clarifies the content and spatial distribution characteristics of trace elements in the near ground,and the risk level was assessment,and combines multivariate statistics and geostatistical analysis to analyze the source of trace elements.The main conclusions are as follows:(1)A study of trace elements in the surface sediments of Hongshe Reservoir in the rare earth mining area of Zhuxi basin found that the surface sediments were composed of silt and sand,the particle size of the reservoir was relatively coarse in the north,south,and east,and relatively fine in the center and west.V,Co,Ni,and Cu were greatly affected by the particle size.The average contents of V,Cr,Mn,Co,Ni,Cu,Zn,As,Cd,Pb and ∑REE in the surface sediments of Hongshe Reservoir were 40.47,27.23,390.26,6.69,10.80,12.37,79.85,7.86,0.15,87.33 and 487.12 mg/kg,Mn,As,Cd,Pb and ∑REE exceeded the soil environmental background values in Fujian.Soil and water loss in the basin aggravated the downstream migration of trace elements,resulting in serious pollution of Cd,Pb,∑REE,Mn and As in the downstream of the mining area.The bioavailable states of Mn,Co,Cu,Zn,As,Cd,Pb and ∑REE were high,which were more harmful to the environment.(2)The research on the trace elements in the soil around the rare earth mining area in Zhuxi basin found that due to the influence of mining activities,the trace elements released in the environment migrated downstream along the river network,resulting in higher content of trace elements in the farmland downstream of the mining area.Whether it is the mining area,the downstream of the mining area or the surrounding area,the main polluting elements were Mn,As,Cd,Pb and ∑REE.The pollution in the downstream and surrounding areas of the mining area is heavier.The pollution in the downstream of the mining area is through the influence of river network runoff,and the pollution around the mining area is through the influence of atmospheric movement and atmospheric deposition.The pollution degree from high to low is the downstream of the mining area > the surrounding area of the mining area > the mining area.The bioavailable states of Mn,Co,Cd,Pb and ∑REE in the three areas were higher;From the mining area to the downstream of the mining area,the bioavailable states of Mn,Cd,Pb and ∑REE increase,and the harm to the environment increases.(3)Geoaccumulation index shows that Cd,Pb and ∑REE had mild to moderate pollution,Mn had mild pollution in the downstream of the mining area,and Cd had medium pollution in the downstream and surrounding areas of the mining area.The results of the potential ecological risk assessment show that the ecological risk of most elements is low,and the potential risk of Cd in the mining area reaches a medium level,while the Cd in the reservoir,downstream of the mining area and around the mining area had reached a strong ecological risk.The order of risk of trace elements was Cd>Pb>As>Co>Ni>Cu>Mn>Cr>V>Zn;the comprehensive potential ecological risk results show that the downstream of the mining area reaches a medium ecological risk,the downstream of the mining area>the surrounding of the mining area>reservoir>the mining area.The results of health risk assessment showed that hand-oral ingestion was the most risky route,Pb had the greatest non-carcinogenic risk,and the order of the total non-carcinogenic hazards of 10 trace elements was Pb>As>Mn>V>Cr>Ni>Co>Cu>Zn>Cd,the non-carcinogenic risk index of children has reached 1,which should be paid attention to by local residents.From the results of the risk assessment code method,Mn,Co,Cu,Zn,Cd and Pb have reached medium to strong ecological risks in all sampling areas.In general,the risk element in rare earth mining areas in Zhuxi basin was Mn,Co,As,Cd,Pb and ∑REE,the ecological risks around the rare earth mining area and downstream of the mining area were relatively high,Affected by the migration of elements,in the process of rainfall,surface runoff,slope confluence,atmospheric deposition,soil erosion,etc.,trace elements form accumulation areas in reservoirs,downstream of mining areas and around,making the surrounding ecological risks higher.(4)Multivariate statistics and geostatistical analysis show that the soil and sediments in the rare earth mining area of Zhuxi basin were affected by regional rock weathering,rare earth mining,breeding activities,use of pesticides and fertilizers,and sewage irrigation.Among them,V,Cr,and Ni were mainly from natural sources of regional rock weathering,Co from the mixed effects of natural sources and mining activities,Cu from the mixed effects of natural sources and farming activities,and Zn from the mixed effect of natural sources,mining activities and farming activities.Cd from the mixed effects of agriculture,mining and farming activities,Mn,As,Pb and ∑REE were mainly from the affected by regional rare earth mining activities. |
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