School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, 510275, China.
School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, 510275, China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Guangzhou, 510275, China.
Environ Pollut. 2021 Oct 15;287:117277. doi: 10.1016/j.envpol.2021.117277. Epub 2021 Apr 30.
Many estuaries have undergone severe saltwater intrusion in addition to simultaneously experiencing serious heavy metal pollution. To explore the effect of water density stratification associated with saltwater intrusion on the behaviour of heavy metals (Cr, Co, Ni, Cu, Zn, As, Pb, and Cd) in water and sediments, a field survey was conducted in a typical estuary (Modaomen). The content, distribution, and mobility of heavy metals were investigated, as well as the influence of environmental factors on their future. The results showed that Modaomen estuary was characterised by a notable variation in salinity along the estuary, presenting total freshwater upstream, high salinity stratification water in the mouth, and saltwater offshore. Dissolved metals presented a prominent gradient vertically, with 1.2-2.1 times higher in bottom water than in surface water and the highest contents in the highly-stratified bottom water. Elevated salinity and restricted mixing induced by water stratification were likely the causes of this outcome. The distribution of heavy metals in sediments was greatly governed by grain size, Fe/Mn (hydr)oxides, total organic carbon, salinity, and dissolved oxygen. Comprehensive evaluation, combined with total contents and chemical fractions of heavy metals, indicated that internal release from sediments contributed a considerable part to the higher levels of heavy metals in bottom water, particularly for Zn and Pb, which was fully consistent with their status in water body, and elevated salinity and lack of oxygen were likely the primary driving factors. During the phase-partition processes between bottom water and sediments, partitioning coefficients were markedly lower in the highly stratified zone, implying that saltwater intrusion facilitated the mobility and repartitioning processes of metals. Because of increased levels and toxicity of heavy metals in water and extended residence time during saltwater intrusion, the potential damage to the estuarine ecosystem should receive more attention.
许多河口除了同时遭受严重的重金属污染外，还经历了严重的盐水入侵。为了探讨与盐水入侵相关的水密度分层对重金属（Cr、Co、Ni、Cu、Zn、As、Pb 和 Cd）在水中和沉积物中的行为的影响，在一个典型的河口（磨刀门）进行了实地调查。研究了重金属的含量、分布和迁移性，以及环境因素对其未来的影响。结果表明，磨刀门河口具有明显的沿河口盐度变化特征，上游为总淡水，河口为高盐度分层水，近海为盐水。溶解态金属在垂直方向上呈现出明显的梯度，底层水的含量比表层水高 1.2-2.1 倍，在高度分层的底层水中含量最高。盐度升高和分层水的限制混合可能是导致这种结果的原因。重金属在沉积物中的分布主要受粒径、Fe/Mn（氢）氧化物、总有机碳、盐度和溶解氧的控制。综合评价，结合重金属的总含量和化学形态，表明沉积物的内部释放对底层水中重金属水平的升高有相当大的贡献，特别是对 Zn 和 Pb，这与它们在水体中的状况完全一致，而高盐度和缺氧可能是主要的驱动因素。在底层水和沉积物之间的相分配过程中，高度分层区的分配系数明显较低，这意味着盐水入侵促进了金属的迁移和再分配过程。由于盐水入侵期间水中重金属水平升高和毒性增加，以及停留时间延长，对河口生态系统的潜在损害应引起更多关注。
