塔里木盆地东南缘绿洲区土壤砷空间分布及农作物砷富集特征

Spatial Distribution of Soil Arsenic and Arsenic Enrichment in Crops in the Oasis Region of the Southeastern Tarim Basin

以新疆塔里木盆地东南缘的巴音郭楞蒙古自治州的若羌县、且末县和和田地区的民丰县、于田县的绿洲区为研究区,采集表层土壤3487组、土壤剖面采样点35组,农产品及根系土壤采样点93组,综合采用数理统计方法、地统计学和GIS技术,研究土壤As的空间分布特征,探讨各类农产品对As富集的影响,比较空间自相关性显著区域和空间自相关性无显著区域内农产品和根系土壤中As的含量特征.结果表明土壤As含量较低,农用地和非农用地土壤As含量均值分别为9. 81mg·kg-1和7. 94 mg·kg-1.表层土壤As含量超过新疆土壤背景值的采样点个数为568个,占总取样点数的16. 3%;超过风险筛选值的采样点个数为5个.土壤As空间自相关的莫兰指数均大于0,空间聚集类型主要以高-高型和低-低型为主,其中高-高型聚集区主要位于各县农用地范围内.GIS空间分布显示,土壤As含量高值区呈片状集中或岛状零散分布.标准差椭圆显示,若羌县土壤As含量变化趋势方向为南北方向,且末县和民丰县土壤As含量变化趋势方向为西南-东北方向,于田县土壤As含量变化趋势方向为西北-东南方向.若羌县农用地土壤垂向剖面上As含量从地表到深层存在波动,其余各县都相对稳定.研究区农作物对As的富集能力表现为:根茎类蔬菜>核桃>小麦>玉米>红枣,玉米和红枣的As含量与根系土的As含量在0. 05水平下呈现显著正相关.空间自相关性显著区和空间自相关无显著区的农产品中的As含量无显著性差异,而两个区域根系土壤的As含量存在显著性差异.

We use 3487 surface soil samples,35 soil profile samples,and 93 agricultural products and root soil samples obtained from the southeastern Tarim basin,Xinjiang,northwestern China( Ruoqiang County and Qiemo County,Bayingguo Mongolia Autonomous Prefecture,and Minfeng County and Yutian County,Hetian Prefecture) to assess As contamination. Multivariate statistical analysis,geostatistics,and global information system( GIS) techniques are used to study: the spatial distribution characteristics of soil As,the effects of various agricultural products on As enrichment,and to compare the characteristics of the As content of agricultural products and root soils in spatially significantly and non-significantly autocorrelated regions. The As content of soil samples were relatively low,and the average As contents determined for agricultural land and non-agricultural land were 9. 81 mg·kg-1 and 7. 94 mg·kg-1,respectively. We found that 568 surface soil samples( 16. 3% of all samples) had an As content that exceeded Xinjiang soil background values( 11. 2 mg·kg-1) and that five samples exceeded the risk screening values( 25 mg·kg-1). The Moran’s indexes of spatial autocorrelation were > 0,and the main aggregation types of spatial autocorrelation of soil As were high-high and low-low types,with the zone of the high-high type being mainly located in the agricultural land of each county. A GIS spatial distribution map showed that the high value area of soil As content presented a flaky or island-like scattered distribution. The standard deviation ellipses showed that the trend direction of soil As content in: Ruoqiang County was from north to south,Qiemo County and Minfeng County were both from southwest to northeast,and Yutian County was from northwest to southeast. The As content of the vertical profiles of the agricultural land in Ruoqiang County fluctuated from the surface to depth,whereas those of other counties were relatively stable. The As enrichment ability of crops was ranked as: root vegetables > walnuts > wheat > corn > red dates. The As contents of corn and red dates showed a significant positive correlation with that of the root soil. There was no significant difference in the As content of agricultural products between significant autocorrelation zones and non-significant autocorrelation zones,whereas there was a significant difference in the As content of root soils.