大气降水对贵州喀斯特地区高背景值土壤镉的释放影响

Influence of Atmospheric Precipitation on the Release of Cadmium from High Background Soils in Karst Areas of Guizhou

大气降水是重金属元素迁移转化的一个重要途径且影响着土壤重金属分布。采集贵州省主要农业土壤进行镉质量分数分析;采集大气降水样品分析降水量、pH、镉质量分数;并模拟降水淋溶对镉释放及形态的影响。结果表明,土壤中镉质量分数差异大且有580组样品超过二级土壤标准,超标率为32%,变异系数最高达145.31%,总体来说,贵州省农业土壤镉质量分数呈现出非均匀分布的特征。镉元素在各层土壤中均值大小顺序是耕作层>心土层>母质层,可见贵州省土壤已受到了明显的镉污染,污染物镉元素大部分富集在土壤表层,即耕作层,给农业生产带来了极大的风险。贵州省降雨量夏季最高,大气降水的pH值在5.9—8.2之间,季节变化上多表现为夏季较高,秋季次之,春冬季较低;从时间上看大气降水中镉质量分数的季节变化性较大,说明其来源不稳定。降水淋溶对不同类型土壤的镉释放效应基本相似,淋滤液中镉质量分数随淋溶量增大而升高,降水有利于镉的迁移活化;土壤淋溶模拟降水pH值越低,镉的释放量越大;不同土样在经过降水淋溶后,土样中镉各形态占比大小顺序为还原态>可交换态>氧化态>残渣态,上层土样所含交换态镉比下层土样少,降水淋溶对表层土壤影响较大。本研究为了解贵州省土壤和降水中镉污染现状提供参考,同时对研究降水对土壤镉分布的影响有重要的意义。

Precipitation is an important way for the migration and transformation of heavy metals and affects the distribution of heavy metals in soil. We collected the main agricultural soils in Guizhou Province for cadmium content analysis, collected atmospheric precipitation samples to analyze precipitation, pH, and cadmium content, and simulatesd the influence of precipitation leaching on the release and form of cadmium. The results showed that, the cadmium content in soil varied greatly and 580 groups of samples exceeded the second-level soil standard, and the coefficient of variation was as high as 145.31%. In general, cadmium presented a non-uniform distribution of agricultural soil quality scores in Guizhou Province. The order of the average value of cadmium in each layer of soil was cultivated layer>heart soil layer>parent material layer. It could be seen that the soil in Guizhou Province had been significantly polluted by cadmium, and most of the pollutant cadmium was concentrated in the surface layer of the soil, that was, the farming layer, which brought great risks to agricultural production. The rainfall in Guizhou Province was the highest in summer, and the pH value of atmospheric precipitation was between 5.9 and 8.2. In terms of seasonal changes, it was mostly higher in summer, followed by autumn, and lower in spring and winter. From the perspective of time, the seasonal variability of cadmium content in atmospheric precipitation was large, indicating that its source was unstable. The effect of precipitation leaching on the release of cadmium in different soils was basically similar. The content of cadmium in the leaching solution increased with the increase of leaching amount. The precipitation was beneficial to the migration and activation of cadmium. The lower the pH value of the simulated precipitation of soil leaching, the greater the release of cadmium. After leaching in precipitation, the proportions of cadmium in different soil samples were in the order of reduced state>exchangeable state>oxidized state>residue state.The upper soil sample contained less exchanged cadmium than the lower soil sample. Rainfall leaching had a greater impact on the surface soil. This study provides a reference for understanding the current status of cadmium pollution in soil and precipitation in Guizhou Province, and is of great significance to the study of the impact of precipitation on the distribution of soil cadmium.