Study On Elemental Geochemistry Of Soils And Their Environmental Impacts In Jiangshan,Zhejiang Province

Based on the data obtained by the 1:50,000 land quality geochemical survey in Jiangshan City,Zhejiang Province,this paper studies the elemental geochemical characteristics and their environmental impact of soils in the Fenglin-Xiakou area The soil geochemical data from the survey covering 280km2 are treated with classical statistical methods according to different geological backgrounds,soil types and soil genesis.The results from random forests approach reveal the main factors controlling the concentration and distribution of soil elements.According to relevant assessment standards,soil quality is evaluated on two aspects:soil environmental quality and nutrient abundance.The SPSS software was used to analyze and establish the relationship models of heavy metals between rice and soils.The ecological effects of heavy metals on rice safety of human health in soils were analyzed,which provides a technique to predect heavy metal concentration in rice and can be used to guide land planning considering its potential ecological risk.The main findings are as follows:(1)The concentration variability of most soil elements in the study area is strong.Th e average concentrations of Cd and Pb are relatively higher,which are 1.9 times and 1.4 times of the Chinese mean values in soils,respectively.The average concentrations of Cd and Hg in the paddy soils derived from the alluvial and flood sediments of the Late Per mian-Early Triassic sedimentary rocks and the Proterozoic intermediate-acidic volcanic rock s-metamorphic complexes are relatively higher.The mean concentrations of As,Cr and Ni in paddy soils located in alluvial and residual slopes are lower than those with other soil formations.(2)The results achieved by the random forests analysis show the geological backgrou nd is the most important factor affecting heavy metal concentrations in soils.The influenc e rate caused by soil genesis on Cd,Hg and Pb is quite high,which means soil genesis i s the main influencing factor.The soil type has a relatively low impact on soil heavy met al concentrations.(3)The spatial distribution pattern of geochemical maps presents that the spatial varia tion of soil pH is weak,and soil organic matter is mainly contolled by soil utilization an d soil types.The distribution of some nutrient elements is affected both by geological bac kground and human interference.(4)The soil elements can be classified into five groups,which are ferrophilic elements,elements bonded to organic matter,rock-forming elements,Cd,Mn and other mutative el ements related to human interference,and sulfophilic elements.(5)Except for Cd,the cleanliness soils of heavy metals As,Cr,Cu,Hg,Ni,Pb and Zn occupy all above 99%of the study area.The nutrient supplement levels of N,P and K in soils are widely scarce in the study area.The integrative soil quality is mainly attrib uted to the third grade which occupies 49.25%of the survey area The total proportion o f the fourth and fifth soil grade occupies nearly 20%,which should be treated with seriou sly as it is of potential ecological risk.(6)There is no significant correlation between the over-standard conditions of heavy m etals in rice and the soil environmental quality of corresponding root soils.The transfer fa ctor of heavy metals in rice refer to plough soils presents that cadmium has the strongest enrichment ability in rice,and lead is the weakest.A multi-regression equation of Cd in s oil-rice system is established,which provides a technique way to predect its potential ecol ogical risk on rice safety and to guide land planning.