黄土高原残塬沟壑区坡耕地土壤重金属分布特征与潜在生态风险评估

Distribution Characteristic and Assessment on the Potential Ecological Risk of Heavy Metal in Slope Farmland Soil on the Loess Gullied-Hilly Area

摘要: 本文选取了黄土高原残塬沟壑区6个坡耕地为样区，分析了表层土壤重金属汞(Hg)、砷(As)、铜(Cu)、铬(Cr)、锌(Zn)、镍(Ni)的分布特征，与黄绵土表土土壤元素背景值进行了比较，结果表明6个坡耕地的铜和锌的含量要大于黄绵土土壤元素背景值，铬、汞、砷和镍的含量要远低于背景值；与土壤环境质量标准(GB15618-1995)相比，耕层土壤中铜的含量仅能达到三级标准，且已远大于使作物减产10%的临界浓度值(100 mg/kg)；其他重金属元素汞、砷、铬、镍和锌在耕层土壤中的含量均达到一级标准。不同坡度坡耕地重金属的变化中，汞与锌的含量随坡度的增大而呈缓慢增长的趋势，其他元素变化相对较为复杂且不规律。由相关性分析可知，Hg和Cu有极显著的负相关性，其他重金属之间不存在显著相关性。采用Håkanson潜在生态危害指数法对样区的重金属潜在生态危险进行评价，结果表明该研究区C_d (多种重金属的富集系数)均大于背景值(6.00)，这说明该区坡耕地存在一定的生态危害程度；6个坡度的坡耕地的潜在生态危害系数中，Cu潜在生态危害系数最高(平均55.612)并达到了中度危害，而其他重金属的潜在生态危害系数数值都很小且均小于1，应注意Cu的污染状况；其潜在生态危害指数均为轻微生态危害；潜在生态危害主要贡献因子为Cu，次之为Zn。

Abstract: In the loess gullied-hilly area on the Loess Plateau, the distribution of the heavy metals including Hg, As, Cu, Cr, Zn and Ni in the topsoil of slope farmland was studied, which was comprised of six slope gradients. Means of heavy metals in the soils collected from six slope farmland were compared with the background values (BV) of soil heavy metals in the loessal soil. The results showed that the average contents of Cu and Zn in the sample soils were higher than the BV, and the content of Cu only reached the third standard of the Environmental Quality Standards for soils in China (GB15168-1995) and was greater than the critical concentration as 100 mg/kg to cause crop fail in 10%, while the contents of Hg, As, Cr, and Zn all reached the first standard of GB15168-1995. The contents of Hg and Zn would increase with the increasing of slope gradient and other heavy metals did not show regularly changing. Correlation analysis indicated that the relation between Hg and Cu was highly significant negative correlation. By using the Håkanson method of potential ecological risk assessment, the C_d (the degree of contamination) of all metals were higher than the BV, the potential ecological risk factor of Cu should be cautioned because which was the highest and achieved moderate degree in the six slope farmland, while the values of the potential ecological risk factor of other heavy metals were all lower than 1. The potential ecological risk indexes were all low, and the main contribution factors were Cu and Zn.