Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, 511458, China; Hong Kong Branch of the Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), School of Energy and Environment, State Key Laboratory of Marine Pollution, City University of Hong Kong, Kowloon, Hong Kong, China.
Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, 511458, China; Hong Kong Branch of the Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), School of Energy and Environment, State Key Laboratory of Marine Pollution, City University of Hong Kong, Kowloon, Hong Kong, China; Research Centre for the Oceans and Human Health, City University of Hong Kong Shenzhen Research Institute, Shenzhen 518057, China.
Sci Total Environ. 2022 Feb 10;807(Pt 1):150712. doi: 10.1016/j.scitotenv.2021.150712. Epub 2021 Oct 6.
The Pearl River Estuary (PRE), the largest estuary in Southern China, regulates the fluxes of riverine trace metals into the South China Sea. However, the geochemical behavior of trace metals in this estuary is still ambiguous. In this study, we investigated the dynamics of trace metals in different phases (i.e., particulate, colloidal and truly dissolved) in the PRE in both wet and dry seasons characteristic of the region. Transformations of trace metals between particulate (>0.45 μm), colloidal (1 kDa to 0.45 μm) and truly dissolved (<1 kDa) phases were observed during the estuarine mixing. Colloidal metals (except for Pb) showed non-conservative 'removal' behavior in the low-salinity zone (S < 10‰), suggesting the coagulation of colloidal metals and subsequent deposition to bed sediments being an important sink of dissolved trace metals. By contrast, truly dissolved metals exhibited a mid-salinity maximum distribution (i.e., Mn, Ni, Cu and Cd) or little variation along the salinity gradient (i.e., Fe). The increase of truly dissolved metal concentration was accompanied by the decrease of particulate metal concentration, indicating that the desorption of suspended particles was an important source of dissolved Mn and Cd in the PRE. Metal released from the suspended particles increased in the dry season due to the high suspended particulate matter concentration. Dissolved Mn concentration in the bottom water in wet season was higher than that in dry season, implying that benthic Mn input increased as the bottom water became hypoxic. Abnormally high concentrations of particulate and dissolved Pb were observed at the lower PRE, implying the presence of a potential point source pollution. A flux model predicted that total dissolved Fe, Ni, Cu and Zn underwent net removal while dissolved Mn and Cd had net inputs during the estuarine mixing. This study raveled contrasting geochemical behaviors of trace metals with different size phases and the different sources and sinks of dissolved metals in the PRE.
珠江口（PRE）是中国南方最大的河口，调节着河流水体中痕量金属向南海的通量。然而，该河口痕量金属的地球化学行为仍不清楚。本研究调查了在该地区具有代表性的干湿两季 PRE 中不同相（即颗粒相、胶体相和真正溶解相）中痕量金属的动力学。在河口混合过程中，痕量金属在颗粒相（>0.45μm）、胶体相（1kDa 至 0.45μm）和真正溶解相（<1kDa）之间发生转化。在低盐度区（S<10‰），除 Pb 外，胶体金属表现出非保守的“去除”行为，表明胶体金属的凝聚和随后的沉积到床沉积物是溶解痕量金属的一个重要汇。相比之下，真正溶解的金属表现出中盐度最大值分布（即 Mn、Ni、Cu 和 Cd）或沿盐度梯度变化很小（即 Fe）。真正溶解金属浓度的增加伴随着颗粒金属浓度的降低，表明悬浮颗粒的解吸是 PRE 中溶解 Mn 和 Cd 的重要来源。由于悬浮颗粒物浓度高，干燥季节悬浮颗粒释放的金属增加。湿季底层水中溶解 Mn 浓度高于干季，这意味着随着底层水缺氧，底质 Mn 输入增加。在下部 PRE 观察到异常高浓度的颗粒相和溶解相 Pb，这意味着存在潜在的点源污染。通量模型预测，在河口混合过程中，总溶解 Fe、Ni、Cu 和 Zn 经历净去除，而溶解 Mn 和 Cd 有净输入。本研究揭示了不同粒径相痕量金属的不同地球化学行为，以及 PRE 中溶解金属的不同来源和汇。
