森林火灾对土壤及水体重金属浓度水平的潜在影响研究进展

Potential impact of forest fire on soil and water heavy metal concentrations: A review

森林火灾(林火)指在林地上自由蔓延的火,是一种自然界中的常见干扰。林火通过消耗凋落物层、燃烧植被、分解土壤有机质和改变粘土矿物等方式,释放出存在于植被与土壤中的金属成分,从而对土壤及水体重金属水平产生一定影响。多数研究结果表明,林火过后土壤中Mn、Cr、Ni、Pb等金属元素浓度短期内存在上升趋势,但不同案例中元素上升程度不同。随着时间的推移,土壤中大多数金属元素浓度可恢复至火灾前的背景值水平。但不同金属元素类型随时间变化的情况也有所不同。形态方面,林火过后多数元素主要以氧化态和有机结合态存在于土壤中。土壤pH和电导率作为土壤火烧严重度的潜在指标,它们的变化与土壤重金属浓度变化是否具有相关性在不同研究中存在较大差异。林火过后,径流水体中大多数重金属浓度水平上升,表明林火增加水体中重金属的潜在生态风险。今后还应开展更多室内与野外控制实验,进一步揭示林火对土壤及水体重金属变化的影响机制,为林业管理和灾害应急管理方面提供更多数据支持。

Forest fire is the free spread fire in woodland ecosystems, and it is one kind of common disturbance of ecosystem. Forest fire can potentially release considerable amounts of metals in vegetation and soils through litter layer consumption, vegetation burning, soil organic matter decomposition, and changing the clay minerals, which can potentially impact the heavy metal concentrations in soils and water. Most of previous studies showed that, after the fire, the concentrations of Mn, Cr, Ni, and Pb in soils were increased in short term to various degrees. With increasing time after fire, most of the metal concentrations recovered to the background level eventually; however, it took various time lengths for different metal species. After fire, most of the metals existed in the forms of oxidized and organic bound fractions in soils. As two indicators for soil burn severity, soil pH and electric conductivity correlated with soil metal concentrations in some studies but not for all. Most of the heavy metal concentrations in water increased significantly after fire, indicating that forest fire had potential ecological risks to water body. Future studies should focus on the laboratory and field controlled experiments to reveal the mechanisms of fire effects on heavy metal concentrations in soils and water, providing more data to support forest management and emergency response of disasters.