原生滩涂植被演替带土壤Cd形态分布及其生态风险评价

为了解原生滨海滩涂不同植被演替带土壤镉(Cd)的含量特征、赋存形态及生态风险,以盐城地区原生滨海滩涂为研究对象,利用BCR 3步提取法分析了不同植被演替带土壤Cd的含量及赋存形态,并采用平均沉积物质量基准系数法(SQG-Q)和风险评价准则(RAC)对Cd的潜在生态风险进行了初步评价。结果表明,原生滩涂土壤中总Cd(CdT)含量在2.21~3.61 mg·kg~(-1)之间,远高于江苏沿海土壤Cd背景值和国家土壤环境质量三级标准;不同植被演替带间,CdT含量表现为互花米草滩碱蓬滩芦苇滩光滩;SQG-Q系数显示该地区土壤CdT处于中等风险,互花米草滩风险相对较高;总体上原生滩涂土壤中可还原态Cd比例较低(12.8%),而酸溶态、可氧化态、残渣态三者差异不大(分别为28.2%、29.8%,29.2%);互花米草滩和芦苇滩酸溶态Cd比例(30.5%、37.0%)显著高于碱蓬滩和光滩(28.2%、20.6%),而残渣态Cd(21.5%、20.9%)则显著低于碱蓬滩和光滩(41.5%、45.6%);RAC评价结果显示,滩涂土壤Cd总体上呈现中等风险,而互花米草滩和芦苇滩达到高风险。以上结果显示,原生滨海滩涂土壤Cd已存在一定的生态风险,其中互花米草滩风险相对较高,随着互花米草的扩张及围垦面积的扩大,其重金属风险值得关注。

Fraction Characteristics and Ecological Risk of Cadmium in Soils of Vegetation Successions of the Pristine Tidal Flat

Fraction, concentration and potential ecological risk of cadmium (Cd) in soils of vegetation successions of the pristine tidal flat in Yancheng were studied. BCR three-stage sequential extraction was run to determine the fraction and concentration of Cd, and sediment quality guideline quotient (SQG-Q) method and risk assessment code (RAC) were used to assess potential ecological risk of Cd. Results showed that concentrations of total Cd (CdT) in the soils ranged from 2.21 to 3.61 mg·kg-1, which exceeded the background value in the coastal zone of Jiangsu Province and the third level of the Environmental Quality Standard for Soils. The concentration of CdT in the vegetation successions was in an order of Spartina alterniflora flat > Suaeda glauca flat > Phragmites australi flat > bare flat. Based on the SQG-Q coefficients, the ecological risk of CdT in the pristine tidal flat was moderate, which was relatively higher in Spartina alterniflora flat than the other vegetation successions. The proportion of reducible Cd was relatively low in the tidal flat (12.8% of CdT), while the other three fractions (acid-soluble, oxidisable, and residual Cd) were little different (28.2%, 29.8%, and 29.2% of CdT). The proportions of the acid-soluble Cd in Spartina alterniflora flat and Phragmites australi flat (30.5%, 37.0%) were significantly higher than those in Suaeda glauca flat and bare flat (28.2%, 20.6%), while the proportion of the residual Cd in Spartina alterniflora flat and Phragmites australi flat (21.5%, 20.9%) were significantly lower than those in Suaeda glauca flat and bare flat (41.5%, 45.6%). As a whole, the ecological risk of Cd in the pristine tidal flat was moderate based on the RAC, while the concentration of Cd in Spartina alterniflora flat and Phragmites australi flat reached a high-risk level. With the expansion of the Spartina alterniflora and the increase of reclamation area, more attention should be paid to the risk of Cd in this area.