| The Heihe River originates from the northeastern part of the Tibetan Plateau in the south of Qilian Mountain. The full-length is 821 km and the basin area is about 14.29 million km2, which make the Heihe River is the second largest inland river in China. The Upper Reaches of the Heihe River is located in the hinterland of the Qilian Mountains, which belongs to the National Nature Reserve, and it is also one of the 50 important national ecological service function areas, with an irreplaceable function of biological diversity and water conservation. At the same time, because the rich mineral resources in the Upper Reaches of the Heihe River, the mining development in the region is intense, which has a great impact on the regionalenvironment. In the northwest ecological environment is fragile and extremely dry conditions, The water and soil resources will be the ties of ecologicah economic and social in the condition of the fragile ecological environment and the fact of lacking water extremely, and it is also the main influencing factors and resistance of the regional economic and of the sustainable development of the environment.The situation of water and soil environment of the Upper Reaches of the Heihe River will have a direct impact on the ecological environment quality, crops and food security and water resources development and utilization way of the middle and lower reaches, it will have a profound impact on the ecological system of the whole basin, however there are less research on the basin’s water and soil environment. In addition, in order to ensure the ecosystem service functionof the Heihe River playnormally, the development intensity of mining activities must be limitedin the controllable scope, which requires the evaluation of the mineral resources’carrying capacity. This paper is a study on the characteristics of water environment geochemistry, soil heavy metal spatial structure and environmental carrying capacity of the areain the west of the Upper Reaches of the Heihe River.This study analyses the hydrogeochemical characteristics and rules of the 5 water ofthe Upper Reaches of the Heihe River (glacier meting water, groundwater, river water, pond water and mine drainage) firstly, evaluating the water quality with the environmental quality standards, revealing the relationship between different water using the comprehensive analysis and isotope method. Then with the method of GS+10 and geostatisticsmethod analyses the structure characteristics and spatial distribution of the heavy metals (Cr, Mn, Ni, Cu, Zn, As, Cd and Pb) of the soil which is not affected by mining and human activities in the study area, exploring the characteristics and direction of variation. It also study the heavy metal interpolation and visualization using the IDW (inverse distance weighted) methods on the ArcGIS platform after the analysis of the relationship between the heavy metal with the multivariate analyses, and compared with the heavy metal content in soil around the miningin order to understand the influence of mine production on the surrounding soil environment. At last evaluations have been conducted using the environmental quality standards, Geoaccumulation Index (Igeo), Enrichment Factor (EF) and Potential Ecological Risk Index (PER1). On this basis, this study evaluates the ability of soil and water environmental carrying capacity on the condition of the development of mineral resourcesand the anti-interference ability. The main conclusions are as follows:Region water environment characteristic and quality:The ion of glacier meting water, groundwater and river water in studied region arevery low in consequence of the leading reason, bedrock weathering. The quality of above water is very well because precipitation is the main recharge. Surface water stays closely with subsurface water and interacts frequently. The ion and TDS of pond water and mine drainage are very high. Extremum concentration exists in individual samples, but the most belongs to saline water. Cation and anion are controlled by rock weathering, also influenced by the strong evaporation and concentration, so the quality of pond water and mine drainage are very poor. The average ion content among the 5 water, the mine drainage is the highest, decreasing by pond water, glacier meting water, river water and groundwater.Heavy metal content and structural characteristics in soil:(1) In natural soil, the distribute of Cr,Ni, Zn, Pb and TOC are mainly influenced by inner factor s(climate, parent material, terrain, soil type and so on).While Cd, Mn, Cu and As may be influenced by extrinsic factors (mining and agricultural activities, traffic pollution, daily living and so on). The changing trend of semivariogram curve of 8 heavy metals and TOC obviously differ in all directions, so anisotropy shows obviously than isotropy in spatial variation of studied region as a result of that. It shows highly heterogeneity in one part, also connects with terrain, flow direction of the Heihe River and the distribution of sampling sites in another.(2) In natural soil, the heavy metal is mostly derived from bed rock and parent material. Among them, Cr and Ni associate closely with As, Zn and Cd have a obvious attendant phenomenon with Pb, Mn is in accordance with Cu in behavior characteristic of geochemistry. Because of the existence of thermokarst, TOC influences the concentration of heavy metal by chelation, especially Ni. The concentration of Cd is extremely high in research area, that because during the process of limestone weathering and regolith formation, CO32- and Cd2+ react into CdCO3 sediment. Another reason is that the production of abundant fine particles during the process of bed stone weathering and regolith formationadsorb Cd2+ and mining activities stripping surface soil and bed stone, speeding up the process of limestone weathering and regolith formation. As a consequence of the high concentration of Cd, most of the research areas belong to higher or high risk zone.Impacts of mining activities on water and soil environment:(1) Mineral resources exploration and development activities in the study areas tripped a lot of topsoil and bedrock. At same time, the weathering of bedrock and soil formation processes were accelerated under the time, the rainfall, temperature and biological activity, resulting in the heavy metal content of the soil increasing surrounded with mines.(2) The surface water was affected by mining activitiesgreatly, especially in small watershed containing mines and the main channel of the Heihe River surrounded with mines, showing that the response toion contentof increase and decrease was obvious and ion content with flow path changed significantly. Because of strong cutting terrain, high elevation drops and fast speed on surface runoff, the surface water purification capacity was strong in the study area and the present situation of the regional water environment was good.(3) The soil analysis located in the mine around showed that heavy metals content in the soil was so high and the mean value was more than that in natural soil. The mean value of eight kinds of heavy metals content was more than 6.7 times with the average in natural soil in which lead (Pb) up to 25 times. The results of the soil environmental quality assessment showed that the indexes of heavy metals were over the standard of the third type of soil, in which exceeding standard rate of Cadmium(Cd) was 100% and the maximum content was over about 70 times.The soil and water environmental carrying capacity:(1) The soil and water environment carrying capacity in high altitude glaciers, especially near the river watershed was low, and the total area of it was about 359.17 km2 accounting for 7.13%of the total area of the study area. The reasons for the low environment carrying capacity in the area was the following main points:These areas were located in high altitude area and the landform undulated terribly; main landform types was bare soil, gravel and bedrock; the annual average temperature was low so as to vegetation, soil and microbial community being not active; permafrost often developed resulting in surface water and groundwater flow being infrequent(2) The area where the soil and water environment carrying capacity was moderate and relatively strong distributed in low mountains, hilly area, river valley and plain where the altitude was relatively low and slope was slow. With elevation lowering and the terrain gradually becoming flat, frozen soil layer was gradually melting and soillayer was gradually thickened. At the same time, the vegetation types and coverage gradually enriched. The runoff, alternateness and update rate between surface water and groundwater was increased. So the ability of bearing mining activities and interference effects was also increased. The area where the soil and water environment carrying capacity was moderate in the Upper Reaches of the Heihe River was up to 1408.45 km2 accounting for 27.96%of the total area of the study area. The area where the soil and water environment carrying capacity was relatively strong was summed to 3269.76 km2 accounting for 64.91%of the total area of the study area. |
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