Abstract:

The iron redox process in soil under anaerobic conditions is closely related to the environmental behavior of heavy metals. However, the interaction of the iron redox and the behavior of copper in calcareous paddy soil is still unclear. In this study, a number of lab experiments were set up to study the reduction and oxidation of iron, activity and speciation of Cu, and the transformation of carbon in calcareous paddy soil with different Cu pollution levels under light and dark conditions. The results showed that the iron reduction process mainly occurred in the calcareous soil under the dark condition, and the maximum rate of iron reduction was inhibited as the increase of the Cu pollution levels, which decreased by 12.28%, 17.54% and 31.58% in light, medium and high Cu pollution, respectively. Moreover, the reduction process of iron under the dark condition reduced the activity of Cu and promoted the transformation of Cu in the soil. The concentrations of 0.5mol∙L^-1 HCl extracted and DTPA-extracted Cu decreased by 99.6% and 96.1% during iron reduction under dark conditions, respectively. The reduction of iron promoted the morphological transformation of Cu in the soil with medium pollution level. No weak acid-extracted Cu was detected while the content of reducible and oxidizable Cu increased by 30.5 times and 25.1 times, respectively, under the dark conditions. Under light conditions, Fe(Ⅲ) reduction occurred first, followed by Fe(Ⅱ) oxidation. Fe(Ⅱ) oxidation was inhibited as the increase of the Cu pollution levels, iron reducting/oxidizing bacteria were the main drivers during the iron redox process in the soil. At the same time, the redox of iron under light conditions can also affect the activity of Cu in soil, the concentrations of 0.5 mol∙L^-1 HCl extracted and DTPA-extracted Cu decreased by 23.0% and 74.5% during iron reduction under light conditions. The oxidation of iron promoted the morphological transformation of Cu in the soil with medium pollution level. The content of weak acid-extracted Cu decreased by 94.5%, while the content of reducible Cu and oxidizable Cu increased by 28.9 times and 18.3 times, respectively, under light conditions. The content of water-soluble inorganic carbon significantly increased, while the content of water-soluble organic carbon decreased after incubation 30 days. A significant positive correlation between the increase of water-soluble inorganic carbon and Cu activity was also found in this study. The results in this study could provide a theoretical basis for the iron redox process and environmental behavior of heavy metals in calcareous paddy soils.

Key words: calcareous paddy soil, ferrous oxidation, ferric reduction, Cu activity, heavy metal

摘要：

厌氧条件下土壤中Fe氧化还原过程与重金属的环境行为密切相关。目前关于石灰性水稻土中Fe氧化还原过程中重金属Cu活性变化仍缺乏系统性研究。采用室内淹水厌氧培养方法,在模拟不同Cu污染程度的基础上,研究光照/避光条件下,石灰性水稻土中Fe氧化还原、Cu活性变化及体系中C转化动力学。结果表明,避光条件下,石灰性水稻土Fe(Ⅲ) 主要表现为还原过程,且随着Cu污染程度的加深,Fe最大还原速率逐渐降低,轻、中、重度Cu污染土壤分别降低了12.28%、17.54%、31.58%,Fe(Ⅲ) 的最大还原速率与Cu的污染程度呈显著负相关关系。同时,Fe(Ⅲ) 的还原过程能够降低土壤Cu活性,促进Cu形态转化,体系中0.5 mol∙L^-1 HCl和DTPA提取态Cu含量分别下降了99.6%和96.1%;以中度污染土壤为例,避光培养结束后,体系未检测到弱酸提取态Cu,可还原态和可氧化态Cu的含量分别增加了30.5倍和25.1倍。光照条件下,体系中Fe的氧化还原表现为先Fe(Ⅲ) 还原、后Fe(Ⅱ) 氧化的过程,随着Cu污染程度的加深,对Fe(Ⅱ) 氧化的抑制作用逐渐增强,铁氧化还原菌是介导土壤Fe氧化还原过程的主要驱动力;同时,Fe氧化还原亦能影响土壤中Cu的活性,体系中0.5 mol∙L^-1 HCl和DTPA提取态Cu含量分别下降了23.0%和74.5%;培养结束后,中度污染的石灰性水稻土中弱酸提取态Cu含量下降了94.5%,而可还原态和可氧化态Cu的含量分别增加了28.9倍和18.3倍。水溶性无机碳（WSIC）增加量与Cu活性降低量之间存在极显著正相关关系。以上研究结果可为石灰性土壤中Fe的氧化还原过程及重金属环境行为提供一定的理论依据。

关键词: 石灰性水稻土, Fe(Ⅱ) 氧化, Fe(Ⅲ) 还原, Cu活性, 重金属