| 九龙江河口咸淡水混合过程中汞的额外增加与消除 |
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| 引用本文： | 张小丹,孙鲁闽,薛凯宁,邹游,弓振斌,袁东星.九龙江河口咸淡水混合过程中汞的额外增加与消除[J].环境科学研究,2023,36(5):922-931. |
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| 作者姓名： | 张小丹 孙鲁闽 薛凯宁 邹游 弓振斌 袁东星 |
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| 作者单位： | 1.厦门大学环境与生态学院，滨海湿地生态系统教育部重点实验室，福建 厦门 361102 |
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| 基金项目： | 国家自然科学基金项目(No.41406120)；福建省自然科学基金项目(No.2019J01035) |
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| 摘 要： | 河口是海陆界面能量和物质交换的重要场所，研究汞在河口的迁移特征及影响因素，对认识汞的生物地球化学行为具有重要意义. 本研究测定了九龙江河口区沉积物孔隙水的总汞(total mercury, THg)浓度与汞同位素特征，结合笔者所在课题组已发表的相关研究数据，比较不同季节、不同潮位、降水与否的表层水THg浓度、汞同位素组成与盐度之间的关系，探究影响表层水中汞额外增加/消除的因素及机制. 结果表明:①孔隙水THg浓度〔(38.28±28.80) ng/L，n=28〕显著高于表层水〔(8.53±6.85) ng/L，n=35〕(P<0.01)；孔隙水THg浓度受季节或径流量变化的影响不明显. 孔隙水δ202Hg平均值(?1.24‰±0.36‰，n=28)处于表层水(?0.32‰±0.38‰，n=29)和沉积物(?1.99‰±0.69‰，n=18)之间；Δ199Hg平均值(?0.13‰±0.03‰，n=28)低于表层水(?0.04‰±0.10‰，n=29)和沉积物(?0.04‰±0.16‰，n=18)，表明汞在孔隙水与沉积物间的双向传递与吸附及非光致氧化过程有关. ②枯水期河口区表层水中的汞以额外消除为主，呈现汞“汇”特征；丰水期则呈现汞“源”特征. 当咸淡水在河道较浅处交汇时，表层水中汞的额外增加更大. 无论是增加或消除，表层水中汞的δ202Hg与Δ199Hg值均升高. 汞在咸淡水交汇界面的迁移受径流量、潮位、河道特征及降水事件等多因素影响. ③枯水期中降水事件发生时表层水THg浓度和汞同位素组成随盐度的变化特征与非降水期不同，表明降水可影响表层水中汞的行为. 研究显示，汞在咸淡水交汇界面的迁移受径流量、潮位、河道特征及降水事件等多因素影响，河口是汞“源”也是汞“汇”.
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| 关 键 词： | 九龙江口 盐度 总汞浓度 汞同位素 孔隙水 |
| 收稿时间： | 2022-08-25 |
Addition and Removal of Mercury in Jiulong River Estuary during Mixing of Seawater and Freshwater |
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| Affiliation: | 1.Key Laboratory of the Coastal and Wetland Ecosystems, Ministry of Education, College of Environment and Ecology, Xiamen University, Xiamen 361102, China2.Key Laboratory of Estuarine Ecological Security and Environmental Health, Education Department of Fujian, School of Environmental Science and Technology, Tan Kah Kee College, Xiamen University, Zhangzhou 363105, China |
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| Abstract: | Estuaries play an essential role in the exchange of energy and materials at the sea-land interface. Studying the migration characteristics of mercury (Hg) and related influencing factors is of great significance for understanding the biogeochemical cycling of Hg. This study assessed total Hg (THg) concentration and Hg isotope compositions in sediment porewater of the Jiulong River Estuary (JRE). Combined with data from relevant published studies published by author′s research group, the relationship between THg concentration, Hg isotopic composition, and surface water salinity in different seasons (wet and dry seasons), different tidal levels, and with or without precipitation events were compared to determine the factors and mechanisms affecting the addition/removal patterns of Hg in surface water. The results showed that: (1) The average porewater THg concentration ((38.28±28.80) ng/L, n=28) was significantly higher than that in surface water ((8.53±6.85) ng/L, n=35) (P<0.01); Porewater THg concentration was not significantly affected by seasons and runoff. On the other hand, the average δ202Hg value of porewater (?1.24‰±0.36‰, n=28) was between that of surface water (?0.32‰±0.38‰, n=29) and sediment (?1.99‰±0.69‰, n=18), while the average Δ199Hg value (?0.13‰±0.03‰, n=28) of porewater was lower than that of surface water (?0.04‰±0.10‰, n=29) and sediment (?0.04‰±0.16‰, n=18), indicating that the bidirectional Hg transfer between porewater and sediment was related to the adsorption and abiotic dark oxidation processes. (2) Hg in the surface water of JRE was mainly removed during the dry season, acting as a Hg sink, while during the wet season, the river estuary was the source of Hg. In addition, significant increases in Hg addition in the surface water were observed when freshwater and seawater converged in the shallow channel. Regardless of the addition/removal pattern of Hg, the δ202Hg and Δ199Hg values increased among almost all samples. The Hg migration at the converge interface of freshwater and seawater was affected by several factors, such as runoff, tide level, channel characteristics, and precipitation events. (3) The variation characteristics of THg concentration and Hg isotopic composition with salinity in surface water during the precipitation period were different from those in the non-precipitation period, indicating the effects of precipitation events on the Hg behavior in surface water during the dry season. It is concluded that Hg migration at the converge interface of freshwater and seawater was affected by several factors, such as runoff, tide level, channel characteristics, and precipitation events. In addition, the river estuary was both source and sink of Hg. |
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