大兴安岭主要林型土壤Zn、Mn形态及潜在生态风险分析

使用BCR连续提取法和重金属形态评价方法(RSP),分别对大兴安岭北部3种主要林型(落叶松、樟子松和白桦)土壤重金属Zn、Mn的形态特征及其潜在生态风险进行分析。BCR连续提取法是将重金属分为以下4种形态:可交换态及弱酸可提取态(EX)、可还原态(RED)、可氧化态(OXI)和残渣态(RES)。RSP表示重金属的污染程度,并将其分为4个等级:无污染,轻度污染,中度污染,重度污染,其值为土壤中次生相中的重金属含量(Msec)与原生相中的重金属含量(Mprim)的比值。研究结果表明:土壤全Mn含量显著高于土壤全Zn含量。3种林型中,落叶松林土壤全Mn含量最高(1169.01±0.74)mg/kg,白桦林最低(470.62±0.65)mg/kg,且3种林型间差异达极显著水平(P<0.01);土壤全Zn含量按降序排列为樟子松林(103.09±0.40)mg/kg>落叶松林(61.02±0.14)mg/kg>白桦林(46.15±0.15)mg/kg。土壤Mn的主要赋存形态为RED-Mn,而土壤Zn的主要存在状态为RES-Zn和OXI-Zn,2种重金属的可提取态比例均大于40%,具有较高的二次释放潜力,且主要分布于表层土壤中。2种重金属的RSP指数为Mn(18.24)>Zn(1.32),均表现为白桦林>樟子松林>落叶松林,且空间分布特征明显。 

Morphology of soil Zn and Mn in main forest types and potential ecological risk in the Great Xing'an Mountains

This study was designed to analyze morphological characteristics of heavy metals in soil such as Zn and Mn and to evaluate their potential ecological risk by methods of BCR and RSP ( rations secondary phase and primary phase) in three typical forest types, namely, Larix gmelinii, Betula platyphylla and Pinus sylvestris var. mongolica in the Great Xing'an Mountains, northeastern China. Heavy metals were divided into the following four morphologies by BCR, extractable, bound to carbonates, bound to Fe-Mn oxides and residual morphology. RSP which indicates the degree of heavy metals pollution was divided into four levels:no pollution, light pollution, moderate pollution, and severe pollution. The value of RSP is expressed by the ratio of the soil heavy metals content (Msec) at secondary phase to that (Mprim) at the primary phase. The results showed that: soil Mn content was significantly higher than soil Zn content. Soil Mn content in L. gmelinii forest was the highest (1 169.01±0.74) mg/kg, while it was the lowest in B. platyphylla forest ( 470.62 ±0.65 ) mg/kg, and their difference was highly significant ( P <0.01);Soil Zn content was ranked in the decreasing order of P. sylvestris var. mongolica forest (103.09±0.40 mg/kg), L. gmelinii (61.02±0.14) mg/kg, B. platyphylla (46.15±0.15) mg/kg. The main existing morphology of soil Mn was RED-Mn, and those of soil Zn were RES-Zn and OXI-Zn. Their proportion of extractable form was both over 40%, with high potential of twice releasing, and was distributed mainly in topsoil. RSP index of Mn ( 18.24 ) was higher than that of Zn ( 1.32 ) , and decreased in the order of B. platyphylla, P. sylvestris var. mongolica forest, L. gmelinii, with apparent characteristics in spatial distribution.