水分条件对生物炭钝化水稻土铅镉复合污染的影响

采用培养试验，探究30% WHC、淹水和干湿交替等3种水分条件下，向Pb和Cd污染水稻土以1%添加量施入水稻秸秆生物炭后重金属的形态变化，为生物炭修复重金属复合污染稻田的水分管理提供科学依据.结果表明，添加生物炭后，淹水和干湿交替可显著提高土壤pH值、可溶性有机碳（DOC）和无定形氧化铁含量（Fe_o）.培养结束后，在添加生物炭的处理中，相较于30% WHC，淹水和干湿交替条件下TCLP提取态Pb含量分别下降31.87%和20.33%，TCLP提取态Cd含量分别下降25.29%和16.07%.淹水条件下弱酸提取态Pb和Cd下降幅度分别为24.78%和20.14%，且弱酸提取态Cd含量随时间逐渐降低.在3种水分条件下，Pb和Cd有效性降低顺序为：淹水 > 干湿交替 > 30% WHC.相关分析结果显示，土壤pH和无定形氧化铁含量均与有效态Pb和Cd呈显著负相关，表明淹水条件下添加生物炭可通过提高土壤pH和无定型氧化铁含量来有效钝化Pb和Cd，具有促进复合重金属污染酸性水稻土中重金属向稳定态转化的协同机制.

Effect of Water Regimes on Pb and Cd Immobilization by Biochar in Contaminated Paddy Soil

An incubation experiment was conducted to explore the influence of 30% water holding capacity (WHC), flooding, and alternate dry-wet conditions on changes in heavy metal fractions with 1% rice straw biochar in Pb and Cd co-contaminated paddy soils, to provide a scientific basis for a water regime of biochar remediation on heavy metal contaminated paddy soil. Results showed that flooding and alternating wet-dry conditions could significantly increase soil pH, the contents of dissolved organic carbon (DOC), and amorphous iron oxide (Fe_o) after adding biochar. Compared with a 30% WHC treatment, when the soil is flooded and alternating wet-dry conditions, the content of the TCLP extractable Pb decreased by 31.87% and 20.33%, respectively, and the content of the TCLP extraction Cd decreased by 25.29% and 16.07%, respectively. Under flooding, the acid soluble Pb and Cd content decreased by 24.78% and 20.14%, respectively, and the acid soluble Cd content decreased over time. The decreasing order of available Pb and Cd content was flooding > alternating dry-wet > 30% WHC. Correlation analysis results showed that soil pH and Fe_o have significant negative correlation with available heavy metals, which means flooding with biochar could effectively immobilize Pb and Cd by increasing soil pH and Fe_o content. Flooding and biochar have a synergistic interaction on promoting the transformation of Pb and Cd to more stable fractions in acidic co-contaminated heavy metal polluted paddy soil.