新疆博尔塔拉河湖流域土壤元素空间变异性及其影响因素

Spatial Variations and Influence Factor Analysis of Heavy Metals in Topsoil of Bortala River Basin, Northwest China

中国西北干旱区是典型的温带大陆性干旱气候区,随着人口增多、工农业的迅速发展,人类活动产生的污染物日愈增多,区域土壤环境安全受到威胁。为了解西北干旱区典型河湖流域表层土壤元素的空间变异性,利用经典统计学及地统计分析对博尔塔拉河湖流域地表40个采样点土壤样品中19种元素的空间变异特征及其影响因素进行分析,并通过富集系数法和Hakanson潜在生态风险指数法对重金属潜在生态风险进行评价。博尔塔拉河流域表层土壤样品中Ba、Mn、V、Pb、Cr、Co、Ni、Cu等元素含量平均值均低于新疆表层土壤元素背景值,其他元素含量平均值均偏高。通过系统聚类分析,可将19种元素分为二组:第一组元素主要包括Al、K、Be、Fe、Co、Cr、Mn、V、Ti、Ba、P、Zn、Pb、Cu、Ni等元素,其中Al、K、Be、Fe、Co、Cr、Mn、V、Ti、Ba等元素为第一亚组,元素P单独为第二亚组,重金属Zn、Pb、Cu、Ni为第3亚组;第2组元素为Ca、Sr、Mg和Na,其中,Ca、Sr、Mg等表生环境中地球化学性质较为活跃的元素为第四亚组,Na单独为第五亚组。地统计学分析表明,Al、Fe、K、Ti、Ba、Be、Mn、V、Ti、Ba等稳定性元素表现为中等或较强的空间自相关。元素P和重金属元素Zn、Pb、Ni、Cu由于受到局部随机因素如耕作施肥、交通、工农业生产等小尺度因素影响,空间结构较为复杂,但整体上还没有破坏区域原有的空间格局。Ca、Mg、Sr在表生环境中地球化学活性较强,除受区域整体自然环境的控制外,还容易受人为耕作、径流等因素的影响导致空间结构性较差。Na由于受到区域自然环境变化和人为耕作的影响,空间结构性较差。最后通过富集系数计算得出研究区Co、Cr、Cu、Ni、Pb、V和Zn等7种重金属的富集系数平均值均低于1.5,表明虽然受到人为活动影响,但富集程度较低。Hakanson潜在生态风险指数分析表明,7种重金属的riE值范围在0.8~25.7之间,平均值均小于5,为轻微污染风险。综合生态风险指数RI值表明博河流域表层土壤中重金属总体处于轻微污染风险水平,但局部采样点仍然存在中等生态风险程度。

The arid region of northwest China is a typical temperate continental drought climate,which is sensitive to the natural environment change and human activities.In recent years,with the development of industry and agriculture,more and more people moved to the region and increased the environment pollution,especially heavy metals pollution that threatened the regional soil environment.Based on the methods of classic statistics and geostatistics,the spatial variability characteristic and influencing factors of19elements from40sampling points of topsoil in Bortala River Basin were studied.The heavy metals pollution in topsoil was assessed using Enrichment Factors and Potential Ecological Risk Index.Descriptive statistics of element concentrations in topsoil showed that the contents of elements(Ba,Mn,V,Pb,Cr,Co,Ni,Cu)are lower than their value of background in Xinjiang,the other element concentrations are higher.Cluster Analysis results showed that the elements of the topsoil can be divided into two groups:the first group includes:Al,K,Be,Fe,Co,Cr,Mn,V,Ti,Ba,P,Zn,Pb,Cu,Ni;among them Al,K,Be,Fe,Co,Cr,Mn,V,Ti,Ba are the first subgroup,P is the second subgroup,heavy metal Zn,Pb,Cu,Ni are the third subgroup.The second group includes Ca,Sr,Mg and Na,the forth subgroup are active elements,includes Ca,Sr,Mg,and Na is the fifth subgroup.And then,the geostatistics analysis indicated that all those19elements exist spatial correlation in the sampling scale;among them,elements Al,Fe,K,Ti,Ba,Be,Mn,V,Ti,Ba and other stability element have a moderate to strong autocorrelation.Although the spatial correlation was influenced by random factors(e.g.cultivation fertilize transportation and other manufacture in the region)P and heavy metals Zn,Pb,Ni,Cu have a complicated spatial characteristic,but not destroyed the primitive structure.Geochemical characteristic of elements Ca,Sr,Mg are strong,in addition to the influence of regional soil parent material,those elements were easily influenced by local factors and lead to complicated spatial structure.Because of the environment change and human farming in region,element Na also has a bad spatial correlation.At last,enrichment factors showed heavy metal Co,Cr,Cu,Ni,Pb,V and Zn are mainly derived from soil parent material.Potential Ecological Risk Index showed that average value of r Ei was all lesser than5,indicated those7heavy metals posed slight or medium ecological risk.The value of RI indicated that slight ecological risk of heavy metals in topsoil of Bortala River Basin,but also exit medium ecological risk in some local sampling sites in study area.