pH值对海陆交互相土壤镉纵向迁移转化的影响

为揭示土壤pH值影响下海陆交互相土壤镉(Cd)纵向迁移转化规律,共布设18组土壤剖面,测定90组海陆交互相不同深度土壤中的pH值及重金属镉含量,运用地质累积指数和潜在生态风险指数法对Cd污染程度进行评价,采用相关分析识别土壤pH值对土壤Cd迁移转化的影响程度.结果表明:广州市南沙区土壤多属于中度-强污染,具有高潜在生态风险,0~20cm土壤中有88.89%的pH≤7.5,有88.89%土壤Cd含量≥0.3mg/kg,随着土壤深度的增加,土壤污染程度及潜在风险程度明显降低;pH值与水溶态Cd相关系数为-0.93(P<0.01),与弱酸提取态Cd相关系数为0.92(P<0.01),随着土壤深度增加,土壤pH值逐渐增大,土壤水溶态Cd逐渐减少,弱酸提取态Cd逐渐增多;中性和碱性土壤可以抑制Cd的纵向迁移,弱酸性和酸性土壤对Cd的吸附量有限,会增加Cd在纵向上的迁移量及迁移深度.研究结果对城市周边农田土壤Cd污染的区域防治、污染土壤治理修复具有重要意义.

Effects of pH on vertical migration of cadmium in the sea land interaction zone

In order to investigate the vertical migration of cadmium (Cd) in the sea-land interaction soil under the influence of pH, a total of 18sets of deep soil profiles (each set sampled at 5different depths) were considered to determine the pH and the content of Cd in soil with different buried depths. Geological accumulation index and potential ecological risk index were used to evaluate the degree of Cd pollution. The Cd pollution degree was evaluated by the method of geological accumulation index and potential ecological risk index, and the correlation analysis was used to identify the influence of soil pH on Cd migration and transformation. The results showed that the soil in Nansha of Guangzhou is medium-high polluted with maximum ecological risk. In 0~20cm soil profile, 88.89% soil pH≤7.5and 88.89% soil Cd content≥0.3mg/kg. Furthermore, the pollution degree and the potential degree of risk of soil showed a negative correlation to the depth of soil. The correlation coefficient between pH value and water soluble Cd was -0.93 (P < 0.01), and that between pH value and weak acid extracted Cd was 0.92 (P < 0.01). Moreover, soil pH value and weak acid extracted Cd increased gradually while the soil water-soluble Cd decreased gradually with the increase of soil depth. Neutral and alkaline soils can inhibit the vertical migration of Cd, while weak acid and acid soils increase the vertical migration volume and migration depth of Cd due to the low adsorption. These results have important significance for the regional prevention and control of Cd pollution in farmland surrounding cities as well as for the treatment and remediation of polluted soil.