典型农业型城乡交错区小型蔬菜生产系统重金属平衡的研究

Budget of Heavy Metals in Small-Sized Vegetable Farming System in a Typical Peri-Urban Agricultural Area

以南京城乡交错区小型蔬菜生产系统为例,研究了1年期间(2003.7—2004.7)蔬菜种植过程中Cu、Pb、Zn、Cd等重金属元素的平衡状况和污染潜力。结果表明:该系统重金属的输入途径主要为施肥和灌溉,施肥特别是有机肥是生产系统重金属输入的主要来源,占输入量的98%以上。重金属年输入量较高,明显高于欧洲农业区水平,而年输出量较低,占输入量的10%以下,在重金属平衡上试验地均表现为盈余。多年的蔬菜种植己导致土壤重金属积累。试验区土壤和蔬菜中的重金属含量均低于国家安全标准,表明蔬菜生产系统现状较安全。综合大气沉降等因素评估表明,本地区Cu、Zn、Cd污染风险较大,且高强度的种植管理会加剧生产系统重金属污染,有可能导致蔬菜地土壤在几十年内即能达到国家土壤环境二级标准。

With the rapid progress of urbanization in China, people are getting more and more concerned about the issue of heavy metals pollution of the soils in peri-urban areas of cities. The balances and pollution potential of heavy metal elements in a small-scale vegetable farming system in the peri-urban area of Nanjing was monitored during the period from July 2003 to July 2004. Results indicated that heavy metals in the soil came mainly via fertilization and irrigation, especially the application of organic manure, which contributed more than 98% of the input. The annual input of the heavy metals in the area was significantly higher than in the farming land of European countries. The annual output, however, was very low, less than 10% of the input, leading to gain of the heavy metals in the plots. Long-term vegetable cultivation has caused accumulation of the heavy metals in the vegetable soils. Fortunately, the concentrations ofCu, Pb, Zn and Cd in the vegetables and soils in the study area were still lower than the set criteria in the national safety standard, indicating that the vegetable farming system is safe under the present circumstances. Evaluation integrating atmospheric deposition showed the soil in the region might have a high risk of Cu, Zn and Cd contamination. Intensive vegetable cultivation will aggravate heavy metal pollution of the soil, and may possibly bring the soil up to the Second Grade of the National Soil Environment Quality Standard within several decades.