非粮化利用下耕地土壤重金属分布特征、生态风险和来源解析

为探索非粮化利用下耕地土壤重金属含量分布特征和潜在生态风险.以非粮化问题突出的环杭州湾典型区域为例,采集并测定254个耕地0～20 cm表层土壤样品,分析粮食、苗木、蔬菜和水果这4种不同耕地利用类型的8项土壤重金属含量分布特征,通过内梅罗综合指数法和潜在生态风险指数法进行生态风险评价,并利用PMF模型解析重金属来源.结果表明,研究区耕地As、Cr、Cd、Cu、Hg、Ni和Zn含量平均值都高于土壤背景值,整体处于轻度污染状态,存在中度生态风险,其中Hg、Cd和As的单因素污染风险相对较高;不同耕地利用类型土壤重金属含量差异显著,潜在生态风险水平依次为：苗木>水果>蔬菜>粮食,非粮化利用会造成一定的重金属污染生态风险;研究区土壤重金属来源包括工业源(36.8%)、自然源(28.4%)、大气沉降源(21.4%)和农业源(13.4%).综合认为,化肥和农药施用量增长是耕地非粮化造成土壤重金属含量升高的直接原因,而耕地周边的工矿企业三废扩散和煤炭等能源燃烧导致的污染物大气沉降,更加速了研究区土壤重金属含量上升.

Distribution Characteristics, Ecological Risks, and Source Identification of Heavy Metals in Cultivated Land Under Non-grain Production

The purpose of this study was to explore the distribution characteristics and potential ecological risks of soil heavy metal pollution of cultivated land under non-grain production. Taking a typical area around Hangzhou Bay as an example, 254 topsoil samples (0-20 cm) of cultivated land were collected, and the content of eight soil heavy metals in four different cultivated land use types, including grain, seedlings, vegetables, and fruits, was analyzed. The ecological risk was assessed by the Nemerow pollution index and the potential ecological risk index, and the PMF model was used to identify the source of soil heavy metals in the study area. The results showed that the average contents of As, Cr, Cd, Cu, Hg, Ni, and Zn were all higher than the soil background value, except for Pb, but were lower than the national risk control standard for soil contamination of agricultural land. Non-grain production had a significant impact on the accumulation of heavy metals in soil. The content of heavy metals in nurseries and orchards was relatively high, followed by vegetable fields, and the lowest in grain fields. The Nemerow index showed that the cultivated land in the study area was in a light pollution level as a whole, and the single-factor pollution risks of Hg, Cd, and As were relatively high. The potential ecological risk levels of heavy metals in different cultivated land use types were:nurseries>orchards>vegetable fields>grain fields. The PMF results showed that the main sources of soil heavy metals in the study area were mixed sources of industrial emissions (36.8%), natural parent material sources (28.4%), atmospheric deposition sources (21.4%), and agricultural activity sources (13.4%). In conclusion, the increase in the application of chemical fertilizers and pesticides was the direct reason for the increase in soil heavy metal content caused by non-grain production of the cultivated land, whereas the industrial and mining emissions and atmospheric deposition accelerated the increase in soil heavy metal content in the study area.