周期性冻融对棕壤理化性质及Pb赋存形态的影响

为探究气候变化背景下周期性冻融对土壤性质及重金属的影响,采用模拟试验,探讨冻融频次对棕壤微团聚体、pH值、电导率(EC)、有机质(OM)、阳离子交换量(CEC)、PO^3-₄、酶活性以及Pb赋存形态的影响,分析了周期性冻融下Pb赋存形态与土壤理化性质间的相关性。结果表明:周期性冻融导致2～0.25 mm颗粒含量降低,0.25～0.05 mm颗粒含量增加,微团聚体稳定性被破坏。随着冻融频次的增加,棕壤pH值,EH,OM,CEC,URE活性升高,PO^3-₄,CAT活性降低。冻融频次增加时,弱酸提取态Pb含量增加(p<0.05),可还原态Pb含量先增后降,残渣态Pb含量先降后增,可氧化态Pb含量呈波动式; 弱酸提取态Pb与PO^3-₄呈显著负相关(p<0.05),残渣态Pb与PO^3-₄呈显著正相关(p<0.05),可还原态Pb与土壤pH值呈显著正相关(p<0.05),可氧化态Pb与土壤OM呈显著正相关(p<0.05)。综上,冻融会通过改变土壤的理化性质从而导致Pb生态毒性增强,从而在一定程度上增加了Pb对深层土壤及地下水的环境风险。

Effects of Freeze-Thaw Cycle on the Physical and Chemical Properties and Pb Transformation of Brown Soil

In order to explore the effects of Freeze-Thaw Cycles on soil properties and heavy metals under the background of climate change, simulated experiments were used to explore the effects of the frequency of the Freeze-Thaw Cycle on brown soil micro-aggregates, pH value, electrical conductivity(EC), organic matter(OM), cation exchange capacity(CEC), PO^3-₄, enzyme activity, transformations of Pb and the influence of each form content, which reveal the correlation between Pb transformations and soil physical and chemical properties under periodic Freeze-Thaw Cycles. The results show that: Freeze-Thaw Cycle disturbance causes a ratio of 2～0.25 mm particle decrease, a ratio of 0.25～0.05 mm particle increase, and the stability of micro-aggregates is destroyed, pH value, EC, OM, CEC and urease(URE)activity of the soil increase, PO^3-₄, and catalase(CAT)activity decrease. Specifically, when the Freeze-Thaw Cycle increases, the content of Acid Soluble Pb increases(p<0.05). It was observed that the content of Reducible Pb first increases and then decreases, the content of Residual Pb happens to be the opposite of reducible Pb, and the content of Oxidisable Pb fluctuates. In addition, the Pb extracted by weak acid and PO^3-₄(p<0.05), the Reducible Pb and soil pH value(p<0.05), the Oxidisable Pb and OM(p<0.05)have a significantly positive correlation respectively. Studies have shown that Freeze-Thaw Cycle can increase the eco-toxicity of Pb by changing the physical and chemical properties of the soil, which increases the environmental risk of Pb to deep soil, groundwater and the atmosphere to a certain extent.