The geochemical behavior of Cu and its isotopes in the Yangtze River

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Title: The geochemical behavior of Cu and its isotopes in the Yangtze River
Authors: Wang, Q
Zhou, L
Little, SH
Liu, J
Feng, L
Tong, S
Item Type: Journal Article
Abstract: Copper (Cu) isotopes can be a useful tool to constrain the interaction of water and the environment, but they have not been widely applied to riverine research in the preceding decades. Isotopically heavy Cu in rivers (global average: about +0.7‰) compared to rocks (at about 0‰) has been attributed to: a) the mobilization of heavy Cu during oxidative weathering, and b) partitioning between an isotopically heavy, organically complexed dissolved pool, and an isotopically light pool adsorbed to particulates. Here, we report Cu concentrations and isotope ratios of the main stream of the Yangtze River and its several tributaries. We find that the Yangtze River exhibits anomalously heavy Cu isotope compositions compared to other rivers: δ65CuNIST 976 of dissolved Cu for the main stream, from Chongqing to Nanjing, ranges from +0.59 to +1.65‰, while the tributaries vary from +0.48 to +1.20‰. A negative correlation is observed between Cu concentrations and Cu isotope compositions. We attribute the anomalous Cu isotope geochemistry of the Yangtze River to two key features of the basin: first, the influence of the Three Gorges Dam (TGD), and second, the presence of extensive Cu sulphide deposits close to the lower reaches of the river. In the upper reaches, downstream towards the TGD, δ65Cu values increase as Cu concentrations decrease, reflecting the preferential adsorption of light Cu by sedimenting particulate phases. δ65Cu values continue to increase to a maximum of +1.65‰ in the middle reaches, at Guangxingzhou. The lower reaches, from Jiujiang to Tongling, are characterized by less positive values of δ65Cu (at about +0.60‰), due to the oxidative weathering of Cu sulphide deposits. The overall Cu-δ65Cu trend in the river reflects mixing of these waters from the lower reaches, influenced by Cu sulphides, with waters from upstream, which have lower Cu concentrations and elevated δ65Cu values.
Issue Date: 1-Aug-2020
Date of Acceptance: 2-Apr-2020
DOI: 10.1016/j.scitotenv.2020.138428
ISSN: 0048-9697
Publisher: Elsevier BV
Start Page: 1
End Page: 12
Journal / Book Title: Science of The Total Environment
Volume: 728
Copyright Statement: © 2020 Elsevier Ltd. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence
Sponsor/Funder: Natural Environment Research Council (NERC)
Funder's Grant Number: NE/P018181/1
Keywords: Environmental Sciences
Publication Status: Published online
Embargo Date: 2021-04-19
Article Number: 138428
Online Publication Date: 2020-04-19
Appears in Collections:Faculty of Engineering
Earth Science and Engineering
Grantham Institute for Climate Change