Geochemical Characteristics And Controlling Factors Of Soil And Stream Sediment In Baoshan Area,Yunnan Province,Southwest China

Soil sustains all terrestrial organisms and is the medium for all biogeochemical processes.However,it is a finite resource that is not renewable on the human time scale.With competing pressures between population,resources and environment,soil quality has become a major concern globally.Soils are mainly composed of complex mixture of weathered products of geological materials.The chemical compositions of soil are influenced by parent geological materials,organisms,climate,relief,time of weathering and pedogenesis,and human activities.The National Soil Pollution Status Survey Bulletin,the Geochemical Survey Report on Cultivated Land of China and National Land Quality Geochemical Monitoring data showed that the environment status of soil in Southwest China is unoptimistic.However,the content,enrichment and depletion characteristic,spatial distribution characteristic and controlling factors of elements in soil,stream sediment and main geologic body are still not been thoroughly researched in Southwest China.The ecological risk of heavy metals in surface soil has not been systematically evaluated.This research is supported by National Geochemistry Survey of Land Quality project?NGSLQ?,1:250000 Land Quality Geochemical Survey of High Geological Background Area,Southwest China,which is funded by China Geological Survey.The Baoshan area were selected as research area to study the element content,enrichment and depletion characteristics and transfer regulations of elements in regional scale in soil,stream sediment,and rocks in main stratum and ores in typical mine areas by compositional data analysis?Co DA?,principle components analysis?PCA?,spatial analysis and enrichment factor?EF?;the spatial distribution and controlling factors of chemical elements in supergene environment?soil and stream sediment?;and the ecological risk of heavy metal in surface soil.The following conclusions were obtained:?1?Comparing to national wide datasets,the soil and stream sediment are enriched in As,B,?Br?,Co,Cr,Cu,Hg,?I?,Mn,?N?,Ni,Sb,?Sc?,?Se?,V,TFe₂O₃ and(C_org.);and depleted in Sr and Na₂O.?2?The controlling factors of chemical elements in soil and stream sediment of the Baoshan area were revealed.Cobalt,Cr,Cu,Ni,Sc,Ti,V,TFe₂O₃ and Mg O are controlled by the distribution of basic igneous rocks?basalts?;As,Hg,Sb,Ag,Cd,Pb and Zn are controlled by mineralization;Ca,Mg,Sr and p H are co-controlled by the epigenic geochemical weathering of carbonate rocks,basalts and Quaternary sediments and land-use types;the biophile element(Br,N,?P?,S,C_org.and TC)in soil are co-controlled by climate?temperature?and fertilization and organisms;while,other elements are normally controlled by clastic rocks and acid-intermediate rocks.?3?The results point to a parent lithological origin and natural enrichment of heavy metals in the Baoshan soils:the enrichment in soils may be due to the removal of mobile elements?e.g.,Ca,Na,Mg,and Sr?,and As,Cd,Cr,Cu,Hg,Ni,Pb and Zn enrichment in epigenetic geochemistry processes.However,mining activities may also contribute to the Hg,As,Sb,Cu,Pb,Zn,Cd contamination in surface soil near the mercury and copper-lead-zinc mining areas.?4?The surface soil samples with heavy metals?As,Cu,Cr,Cd,Ni,Pb,Hg,Zn?which were exceed the risk screening values for soil contamination of agricultural land of the People's Republic of China are mainly forming from carbonate,basalt,and ores parent geological materials.The surface soil near mining areas has higher enrichment factors and higher extractable Cd and Pb content and ratio.It is important to monitor the soil forming from carbonate and basalt parent materials and near mining areas to ensure the ecological security of land quality.