三峡库区消落带沉积物-水界面汞的扩散特征

通过模拟实验研究了三峡库区消落带沉积物-水界面汞及甲基汞的扩散。结果表明,三峡库区消落带浅水沉积物中的甲基汞占总汞的比例为0.41%±0.29%,深水沉积物中的甲基汞占总汞的比例为0.74%±0.52%。深水沉积物比浅水沉积物具有更高的甲基汞产率。随着淹水时间的延长,沉积物中甲基汞的含量呈指数增长。沉积物中的甲基汞生成动力学方程符合零级反应方程。沉积物中无机汞的扩散以Freundlich修正式拟合效果最好,相对好氧的环境更有利于沉积物中无机汞的释放。相应地,甲基汞的扩散以抛物线扩散方程拟合效果最好,黑暗厌氧的环境更有利于沉积物中甲基汞的释放。三峡库区消落带沉积物-水界面无机汞的扩散通量为154.65±47.12~160.23±56.19 ng/(m~2·d),甲基汞扩散通量为7.61±3.39~7.79±4.56 ng/(m~2·d)。随着淹水时间的增加,孔隙水无机汞及甲基汞向上覆水体的释放通量均表现为先增加后减小的趋势。沉积物中的甲基汞对上覆水体甲基汞含量的贡献率为1.5%~14.3%,释放量为0.28~0.85 kg/a。而沉积物中的汞对上覆水体汞含量的贡献率为0.20%~1.70%,释放量为5.64~17.55 kg/a。

The Diffusion Flux of Mercury at Water/Sediment Interface in Water-Level-Fluctuating Zone of the Three Gorges Reservoir

The diffusion flux of mercury and methylmercury at water/sediment interface of the Three Gorges Reservoir was studied by simulation experiments in laboratory. Results show that MeHg/THg ratio in shallow sediment and deep-water sediment are 0.41±0.29% and 0.74±0.52% during flooding periods, respectively. Shallow reservoir sediment has higher methylation potential than that of deep-water reservoir sediment. With increasing flooding time, the content of methylmercury in sediments increases exponentially. The diffusion of inorganic mercury in sediments is best fitted by model of Freundlich. The relatively aerobic environment is more favorable for the release of inorganic mercury in sediments. Accordingly, the diffusion of methylmercury in sediments is best fitted by model of Parabolic. Dark and anaerobic environment is more conducive for the release of methylmercury in sediments. The diffusion flux of dissolved mercury and methylmercury are 154.65±47.12-160.23±56.19 ng/(m²·d) and 7.61±3.39-7.79±4.56 ng/(m²·d) at water/sediment interface in water-level-fluctuating zone of the Three Gorges Reservoir, respectively. With the increase of flooding time, the pore water of inorganic mercury and methylmercury fluxes to the overlying water increases first and then decreases. The contribution rate of methylmercury in pore water and overlying water are 1.5%-14.3% and 0.28-0.85kg/a, respectively. At the same time, the contribution rate and amount of mercury in pore water and overlying water are 0.20%-1.70% and 5.64-17.55 kg/a, respectively.