渝西经济区土壤地球化学基准值与背景值及元素分布特征

基于渝西经济区多目标区域地球化学调查资料,采用正态和对数正态法,获得了土壤54种元素(指标)的地球化学基准值和背景值,并研究其分布特征;同时分析了岩石风化成土过程元素的富集贫化规律,以及表层土壤元素分布特征。结果表明,与全国土壤相比,该区重金属元素Cd、Cr、Hg、Ni基准值较高,As较低,Pb、Zn、Cu与全国值相当;多数重金属元素和植物营养元素背景值偏高,仅K、Mn、P、Cl元素背景值低于全国水平。对比土壤背景值与基准值,发现多数元素(指标)背景值与基准值相当,说明表生作用和人为活动对表层土壤影响较小;而Se、Hg、S、N等14种元素在表层土壤富集,人为输入作用显著。不同母岩区表层土壤元素(指标)分布表现为,碳酸盐岩区多数元素含量较高;就不同pH值范围而言,CaO、MgO、K2O、P以及除Hg以外的重金属元素均在碱性环境含量较高,SiO2在酸性环境含量高,较多元素(指标)在中性环境中趋于稳定。

Element Geochemical Baseline and Distributions in Soil in Chongqing West Economic Zone, China

In this paper, we calculated geochemical baseline and background values of 54 elements (indicators) in soil with the method of normal distribution and logarithmic normal distribution, analyzed enrichment or dilution of main elements in the course of weathering and pedogenesis of rocks, and discussed geochemical characteristics of elements in surface soil, based on multi-purpose regional geochemical survey on Chongqing West Economic Zone. Results show that compared with national values, for heavy metals baseline values, Cd, Cr, Hg, and Ni are higher, As is lower, and Pb, Zn, and Cu are approximately equal to their national values. The background values of most elements (indicators) are higher, only K, Mn, P, and Cl are lower. The differences between baseline and background values of most elements (indicators) are not obvious, due to slight hypergenesis effect and human activities; however, fourteen elements, such as Se, Hg, S, N, and etc, are enriched in surface soil because of obvious anthropogenic input. As for as different mother rocks, the contents of many elements (indicators) in surface soil are higher in carbonatite zone. For the pH value, CaO, MgO, K₂O, P and heavy metal elements, except Hg, are higher under alkaline conditions, SiO₂ is higher under acidic conditions, and more elements are tending to being stable in neutral conditions.