韩江三角洲典型地区表层土壤汞的分布特征

Distribution characteristics of surface soil mercury in typical area of the Hanjiang Delta, Guangdong, China

以韩江三角洲典型地区揭阳市为研究区域,共采集表层土壤样本1330个,深层土壤样本331个,分析土壤汞含量,利用富集因子法研究揭阳市土壤汞的污染特征;利用半变异函数模型和局部Moran I法分析土壤汞的结构特征;利用GS+软件中的半变异函数模型和ArcGIS软件支持下的克里金插值法,得出研究区土壤汞含量分布图;探究不同成土母质和不同土地利用类型土壤汞含量的分布特征以及土壤理化性质对汞含量的影响.结果表明,揭阳市表层土壤汞的平均含量为0.079 mg·kg-1,变幅为0.008—1.053 mg·kg-1,高于研究区土壤背景值.研究区土壤汞污染不太严重,只有少部分地区处于中度污染或显著污染,无强烈污染和极强污染.研究区土壤汞含量存在强的空间相关性,说明汞具有强的迁移性.研究区土壤汞含量空间分布格局总体上呈现东北部最高并向四周逐渐降低的趋势.不同成土母质发育的土壤汞含量存在显著差异,成土母质为第四纪沉积物的土壤汞含量显著高于页岩、花岗岩、凝灰岩和粉砂岩发育的土壤.不同土地利用类型的土壤汞含量也存在显著差异,建设用地土壤汞含量显著高于未利用土地和农田用地.有机碳(SOC)和pH值均与土壤汞含量呈极显著正相关,且pH与汞的相关性(r=0.288,P<0.01)略强于SOC与汞的相关性(r=0.257,P<0.01).

Jieyang City, a typical area of the Hanjiang Delta, was selected as the study area. A total of 1330 topsoil samples and 331 bottom soil samples were collected and analyzed for mercury content. The characteristics of the mercury pollution in this area were analyzed by the enrichment factor method. We use semi-variogram fitting and Moran index methods to investigate the structural characteristics of soil mercury content. The semi-variogram model in GS+ and Kriging interpolation supported by ArcGIS were employed to study the spatial distribution of soil mercury content in the target area. The distribution characteristics of mercury content in topsoil of different parent materials and different land use types, as well as the influence of physicochemical properties of soils on the mercury content were explored. The results were as follows: The average mercury content of topsoil in Jieyang city was 0.079 mg·kg-1 with the range of 0.008—1.053 mg·kg-1, which was higher than the background value of soil in the study area. Mercury pollution in the topsoil of the study area was not serious. Only a few areas were moderately or significantly polluted, with no area of strong pollution or extremely strong pollution. A strong spatial correlation of mercury content existed in the topsoil of the study area, suggesting the strong migration ability of mercury. The spatial distribution pattern of mercury content in the study area indicated that the content was highest in the northeast area, while the content in the surrounding areas gradually decreased. The soil mercury contents from different parent materials were significantly different, in which the mercury content of soil from quaternary sediments was significantly higher than that of shale, granite, tuff and siltstone. The mercury contents in soil of different land use types were also significantly different, in which the mercury content in soil of construction land was significantly higher than that of unused land and farmland land. The organic carbon and pH values were significantly positively correlated with soil mercury content, with the correlation between pH and mercury(r=0.288, P<0.01) slightly stronger than that between SOC and mercury(r=0.257, P<0.01).