再悬浮作用下长江口近岸沉积物中Cd、Pb和Cr的迁移与释放

Transport and Release of Cd,Pb and Cr from the Yangtze Estuarine Sediments During Sediment Resuspension Event

利用PES(particle entrainment simulator)模拟装置,实验测定了不同的扰动强度和时间对长江口沉积物中Cd、Pb和Cr再悬浮释放和迁移的影响.在再悬浮过程中,上覆水中溶解态Cd、Pb和Cr的质量浓度分别在0.015～0.157、0.013～0.890和0.066～1.468μg.L-1之间变化,颗粒态Cd、Pb和Cr的含量分别在0.37～5.40、8.3～137.1和31.6～557.7μg.g-1之间变化.在柱样表层生物膜未破坏以前,生物膜上吸附的Cd向上覆水中发生了大量释放,当部分生物膜被破坏以后,沉积物中的Pb和Cr才向上覆水中发生短期的大量释放.物理扰动强度是影响颗粒态重金属含量变化的主要因素.再悬浮释放通量分析发现,通过再悬浮过程释放到水体中的Cd、Pb和Cr,会被再悬浮颗粒重新吸附,并在水动力条件减弱后,逐渐沉降到底部沉积物中,对长江口水生生态系统的危害性较小.再悬浮过程中Cd、Pb和Cr主要通过以下过程完成迁移转化,包括生物膜上吸附重金属的解吸释放、孔隙水中溶解态重金属的直接再悬浮和扩散释放、沉积物中硫化物结合态重金属的氧化释放、上覆水中悬浮颗粒对重金属的吸附以及沉淀等过程.

The effects of resuspension energy and duration on release and transport of sediment bound Cd,Pb and Cr in the southern coastal areas of Yangtze Estuary were analyzed experimentally using a particle entrainment simulator（PES）.In the sediment resuspension experiment,concentrations of dissolved Cd,Pb and Cr in the overlying water were 0.015-0.157,0.013-0.890 and 0.066-1.468 μg·L-1 respectively,and concentrations of particulate Cd,Pb and Cr varied between 0.37-5.40,8.3-137.1 and 31.6-557.7 μg·g-1 respectively.Before the biofilm in column surface was not damaged by disturbance,a large number of Cd adsorption to biofilm was released to the overlying water during the resuspension,but after part of the biofilm was damaged with the enhanced disturbance energy,Pb and Cr were released from the sediments to overlying water in short term.Intensity of physical disturbance was the main factor that influenced the variation of particulate heavy metal concentrations.Results of resuspension fluxes showed that Cd,Pb and Cr released to the water by resuspension were then re-adsorption to suspended particles,and gradually deposited in the bottom sediments when the hydrodynamic conditions weakened,which had less harm to the aquatic ecosystems of Yangtze Estuary.The resuspension process of Cd,Pb and Cr mainly includes the following migration and transformation process： adsorptions of heavy metals in biofilm,direct release and diffusion of dissolved heavy metals from pore water,oxidative release of sulfide associated metals in sediments,re-adsorption of heavy metals to suspended particles in overlying water and deposition of particulate heavy metals.