长江下游南京段典型潮土镉富集以及生物有效性影响因素研究

以长江下游南京段某典型潮土分布区为研究区,通过2014年与2003年两期表层土壤镉等相关成分变化、土壤剖面对比、地球化学统计分析等方法研究了潮土镉富集机制及其生态有效性的主要影响因素。结果表明:相对于2003年,研究区表层潮土2014年镉平均含量增加了40.9%。以中国土壤环境质量标准(GB 15618—1995)为参照,有超过50%的土壤样品达到镉轻度污染水平,且有约25%土壤样品的生物有效镉含量接近或高于当地潮土镉背景值。地学统计分析与实际调查表明,土壤镉与硫以及有机碳呈显著正相关关系,镉最主要的外源可能是受粉煤灰影响的大气降尘。潮土镉活化主要受碳酸盐、Ca、Mg、p H和有效Fe的影响,其中碳酸盐的影响最为重要。研究区含碳酸盐土壤与贫(无)碳酸盐土壤(含量<5 g·kg-1)的Cd含量没有显著差异,但生物有效镉含量以及镉活化率却存在显著性差异,贫(无)碳酸盐土壤的生物有效镉含量和镉活化率分别是含碳酸盐土壤的2.5倍和近2倍。研究区表层土壤发生了酸化(p H平均水平从2003年的7.72下降到2014年的6.96),为控制酸化及预防可能的土壤重金属生态风险,应及时开展土壤生态平衡修复工程。

Cadmium Accumulation and Main Factors Influencing Cadmium Bio-availability in Fluvo-aquic Soils from Lower Region of the Yangtze River

Accelerated industrialization has brought a considerable amount of cadmium(Cd) into soils, resulting in Cd accumulation in the topsoil. Here we studied Cd accumulation and main factors influencing Cd bio-availability in fluvo-aquic soils in the lower region of the Yangtze River, a soil Cd anomaly zone. The results show that Cd accumulation occurred in the topsoil during 2003~2014, with soil Cd average concentration increased by about 40.9% relative to that in 2003. More than 50% of the soil samples had Cd concentration up to light pollution level, according to the Chinese soil environmental quality standards. Cadmium was significantly correlated with S and TOC in the soils. The most possible extraneous source of Cd in the topsoil was atmospheric deposition, which was influenced by fly ash. Soil Cd bio-availability was mainly influenced by soil carbonate, pH, Ca, Mg and Available Fe, with carbonate being the most important factor. Soil Cd concentrations did not differ significantly between carbonate- and non-carbonate soils(carbonate concentration < 5 g·kg^-1), but bio-available Cd and Cd activation rate were significantly different. The average bio-available Cd and activation rate in non-carbonate soils were 2.5 and 2 times that of carbonate-contained soils, respectively. In addition, acidification occurred in the topsoil during the past. This study suggests that it is necessary to execute ecological restoration to control the acidification and prevent the risk of soil heavy metals pollution.