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菜子湖湿地土壤重金属分布、来源及生态风险评价

Distribution, sources, and ecological risk assessment of heavy metals in soil of Caizi Lake Wetland

  • 摘要: 重金属污染已成为威胁湿地生态安全的关键问题之一。为了揭示菜子湖湿地土壤重金属累积现状,对菜子湖湿地表层(0~20 cm深度)土壤重金属含量分布开展研究,使用PMF模型进行重金属来源解析,并评估菜子湖湿地重金属的生态风险。研究结果显示,土壤中重金属的积累程度存在差异,Co、Cr、Cu、Hg、Ni、Pb和Zn平均质量比分别为19.04 mg/kg、75.27 mg/kg、27.26 mg/kg、0.05 mg/kg、28.91 mg/kg、30.55 mg/kg和77.01 mg/kg,各元素含量的变异系数介于29.07%~42.62%之间,其中Ni含量的变异系数最大。在枯水期,除Hg外,泥滩土壤中其他重金属含量均较高;农田土壤中的Hg含量在3个水文时期均较高。菜子湖土壤重金属主要来源于农业源、工业和交通复合源、矿产开采源以及自然来源。菜子湖湿地土壤重金属污染程度总体较低,Co的污染程度最高,41.82%的样品为轻度及以上污染。枯水期土壤重金属污染程度最高,综合生态风险指数表明重金属含量均在轻微风险范围内,生态风险较小。

     

    Abstract: Heavy metal contamination has emerged as a critical threat to global wetland ecosystems, posing significant risks to biodiversity, water quality, and overall ecological security. This study focuses on the Caizi Lake Wetland to elucidate the current status, sources, and associated ecological risks of heavy metal accumulation in its soils. Specifically, we investigated the spatial distribution of heavy metals (Co, Cr, Cu, Hg, Ni, Pb, Zn) in surface soil layers (0-20 cm). To accurately apportion the contributions from various sources, the Positive Matrix Factorization (PMF) receptor model was employed. Subsequently, a comprehensive ecological risk assessment was conducted to evaluate the potential environmental hazards. The findings revealed distinct patterns in heavy metal accumulation. The measured average concentrations were 19.04 mg/kg for Co, 75.27 mg/kg for Cr, 27.26 mg/kg for Cu, 0.05 mg/kg for Hg, 28.91 mg/kg for Ni, 30.55 mg/kg for Pb, and 77.01 mg/kg for Zn. Analysis of variability showed coefficients of variation (CV) ranging from 29.07% to 42.62%, with Ni exhibiting the highest spatial variability (CV=42.62%). This moderate to high variability strongly suggests differential influences from anthropogenic activities across the wetland area. Spatial distribution analysis further indicated that during the dry season, mudflat soils contained elevated levels of all studied heavy metals except for Hg. In contrast, Hg concentrations in farmland soils remained consistently and relatively high throughout all three monitored hydrological periods (dry, normal, and wet), highlighting a distinct contamination pattern for this element. Source apportionment using the PMF model identified four primary contributors to the soil heavy metal burden. These sources were quantified as agricultural activities, predominantly associated with the use of fertilizers, pesticides, and irrigation; a combined industrial and traffic emission source, likely related to nearby manufacturing, energy production, and vehicle exhaust; mineral mining and associated weathering processes; and natural pedogenic origins, deriving from the parent geological material. Regarding pollution and risk levels, the overall degree of heavy metal contamination in the Caizi Lake Wetland soils was assessed to be relatively low. Among the elements, Cobalt (Co) presented the highest level of pollution, with approximately 41.82% of the sampled sites reaching a rating of mild pollution or higher. Temporally, the dry season was identified as the period with the most pronounced pollution status for most metals. Crucially, the calculated comprehensive potential ecological risk indices for all samples fell consistently within the slight risk category. This indicates that, under current conditions, the combined ecological risk posed by the mixture of heavy metals in the Caizi Lake Wetland is minimal. However, the identified anthropogenic influences, particularly in specific zones like farmlands for Hg and mudflats during dry periods for other metals, warrant continuous monitoring to prevent future risk escalation. This study provides a scientific basis for targeted soil management and pollution control strategies in this ecologically sensitive wetland area.

     

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