酸雨区不同用地类型土壤有效态Cd含量季节变化及关键影响因子

探明污染土壤重金属有效态含量的季节变化特征及其敏感影响因子,对农业生产过程中减低重金属生态风险具有重要的参考价值.研究于湘江中下游典型Cd超标农业小流域中选取稻田、旱作蔬菜地、丘陵林地这3类主要用地类型,分析不同用地类型Cd活性的季节变化特征及其与土壤基本理化参数的关联.为期1 a的原位监测结果显示,研究区为典型酸雨区,雨水p H值呈现冬、春季节低于夏、秋季.稻田土壤总Cd含量显著高于旱作蔬菜地,菜地显著高于林地,3种用地类型土壤总Cd含量季节特征相似,均为夏秋季节略低于冬春两季.3种用地类型Cd有效态季节变化与总Cd含量无明显的相关性,稻田土壤有效态Cd含量在5~9月的作物生长季明显低于其他月份,而菜地和林地则恰好相反.稻田土壤Cd有效性的最关键影响因子为Eh,呈显著正相关,与土壤p H负相关,菜地土壤与土壤TOC明显负相关,而林地土壤Cd有效性与水溶性有机碳、TOC呈现明显的正相关关系.研究可为Cd超标土壤污染阻控与农业安全生产提供一定的数据参考.

Major Factors Influencing the Cd Content and Seasonal Dynamics in Different Land Cover Soils in a Typical Acid Rain Region

Understanding the seasonal variations in active heavy metal components and sensitive impact factors is of importance for the ecological risk reduction during the agricultural production processes. Paddy fields, vegetable lands, and hilly forests were selected as three main land cover types to assess the seasonal characteristics of Cd bioavailability and reveal how or to what extent it was affected by the physiochemical parameters of soils, under different land-use types in a typical Cd-contaminated watershed in the middle and lower reaches of Xiangjiang River. One-year in situ monitoring results showed that natural rainfall pH in winter and spring was lower than in summer and autumn in the study region. The total Cd content of paddy soils was significantly higher than that of the vegetable soil, while the hilly forest soil showed the lowest total Cd value. Similar seasonal variations in total Cd content were found in three soil types with slightly lower summer and autumn concentrations than spring and winter values, but no obvious correlation was detected between the total and the available Cd components. The paddy soil available Cd concentration during the 5-9-month crop growth season was significantly lower than the other months of the year, while vegetable cultivation and hilly forest soils showed the opposite trend. E_h was the key factor that had a positive influence on the Cd activity in paddy soil. Soil TOC concentration was negatively correlated with soil activity in vegetable soil. TOC, water soluble organic carbon, showed a significant positive correlation with Cd effectiveness. The results provide scientific references for Cd contamination control and safe agricultural production.