贵州草海湿地不同水位梯度沉积物中汞、砷形态分布及风险评价

通过改进Tessier连续提取法对贵州草海黑颈鹤栖息地不同水位梯度下沉积物汞(Hg)、砷(As)形态及生态风险进行了研究.结果表明,草海湿地沉积物中Hg含量在0.45～1.51-mg/kg之间,超过国家土壤环境质量农用地土壤风险管控标准;形态组成上,残渣态汞(Res-Hg)有机结合态汞(Org-Hg)碳酸盐结合态(Car-Hg)铁锰氧化态(Fe-O-Hg)可交换态(Ex-Hg),不同水位梯度下含量和赋存形态在不同区域不一致.As含量在16.4～23.8-mg/kg之间,形态依次为残渣态砷(Res-As)有机结合态砷(Org-As)铁锰氧化态砷(Fe-O-As)碳酸盐结合态砷(Car-As)可交换态砷(Ex-As).-As含量与贵州省土壤背景值持平,随着水位梯度的抬升,其总量呈增加趋势,残渣态占比逐步增多,性质逐渐稳定.采用地积累指数(I_(geo))、潜在生态风险指数(E_r~i)、风险评价编码法(RAC)对Hg、As的危害程度进行分析表明,基于草海较高Hg环境背景值,Hg整体污染风险较高,As处于低水平的污染风险等级且对环境影响较小.该研究揭示了不同水位梯度下Hg、As总量及形态分布特征,对草海湿地水位抬升恢复湿地提供了参考.

Speciation distribution and risk assessment of Hg and As in sediment of Lake Caohai wetlands under different water level gradients, Guizhou Province

The speciation and ecological risk of sediment Hg and As in different water-level gradients of the Grus nigricollis habitat in Lake Caohai wetland, Guizhou Province were analyzed by modified Tessier sequential extraction. The results showed that Hg content in sediments ranged from 0.45 to 1.51 mg/kg. In terms of speciation composition, residual Hg > Organic Matter Hg > Carbonates Hg > Fe-Mn Oxides Hg > Exchangeable Hg. The content exceeds the soil environmental quality risk control standard for soil contamination of agricultural land and is related to the regional geological background and human activities. There is no regularity in the content distribution on the water level gradient. The ratio of non-residue Hg in Liujiaxiang (zone A) and Huyelin (zone C) area increased with the water level gradient, while the non-residue Hg in Zhujiawan (zone B) showed a downward trend. The As content is between 16.4 and 23.8 mg/kg, and speciation distribution residual As > Organic Matter As > Fe-Mn Oxides As > Carbonates As > Exchangeable As. The As content is equal to the land background value of Guizhou Province. With the water level gradient rises, the total content increases, the proportion of residual increases gradually, and the nature gradually stabilizes. The geo-accumulation (I_geo), the Hakanson index (E_rⁱ), and the risk assessment code (RAC) analyses of the hazard degree of Hg and As indicate that the risk of Hg pollution is high based on high Hg environment background value in Lake Caohai wetland, As is at a low level of pollution risk level and less affected to the environment. In this study, the distribution of Hg and As speciation and ecological risks on different water level gradients of Grus nigricollis habitat in Lake Caohai wetland were studied, and the effects of water-level gradient on heavy metal/semimetal distribution in sediment/soil were discussed. It provides a reference for the assessment of ecological effect of water level rise in the Lake Caohai wetland.