长江流域河水地球化学：人为活动影响与流域化学风化的Sr和B同位素研究-文献详情-维普官网

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长江流域河水地球化学：人为活动影响与流域化学风化的Sr和B同位素研究认领

作者：

Benjamin Chetelat

学位授予单位：

中国科学院地球化学研究所

摘要：

Under the influence of meteoric Water and other factors like glaciers，wind and vegetation, continents are continuously subjected to erosion．Rainwater and surface water interact with minerals of the Earth's surface，resulting in the dissolution of primary minerals and the production of secondary clays and iron or aluminum-oxides that accumulate in soils．Erosion is not only important at a geological time scale，responsible for the landscape evolution but also a key procession the soil formation and stability．Therefore，erosion has important consequences for agriculture and human sustainable development．<br>　　 The study of me dissolved load of rivers provides information on chemical erosion processes(Gaillardet et a1.,1999b；Dalai et a1.,2002；Wu et a1.,2005 and references therein),in particular on velocity of soil formation．The study of sediments(in suspension or at the river bed) is important for understanding the physical processes, in particular the rate of soil erosion(natural or not)．Based on chemical mass balances between the solid phase and the dissolved load of rivers(Craillardet et a1.,1999a；Dosseto et a1.,2008 and references therein),geo-scientists are able to deduce fundamental information about the Earth's surfaces dynamics．For example, chemical weathering of silicates is the dominant long-term sink for atmospheric C02 and thus the dominant regulator of the green-house effect over geological time-scales(Berner et ai.,1983；Raymo et a1.,1988；Godderis and Francois,1995；Godderis et a1.,2003；Dessert et a1.,2003)．Hence，quantifying chemical weathering rates is essential for understanding Earth's long-term climatic evolution.<br>　　 The Changeling basin is particularly well suited for qimtifying erosion processes because it is One of the world largest rivers and averages erosion processes over a huge surface of the Earth(1.81×106km2，19％ of China)．The Upper Changjiang drains the Tibetan Plateau, and provides abettor understanding of the way and rate at which the erosion of the Tibetan plateau Irroeeeds．Units lower part, the Changjiang drains one of the most populated areas of the world and is affectedly the Three Gorges Dam（TGD),the biggest dam in the world．The Changijiang integrates anthropogenic pollution over a large surface area．Better knowledge of its chemical composition and solid transport is critical to understanding how human activities have changed the river chemistry and soil erosion．The Earth is experiencing a unique global climatic change due to the anthropogenic inputs to the atmosphere of greenhouse gases and sources of acidity．Large rivers will clearly respond and change accordingly and therefore，changes to the Changjiang basin should be documented extensively．The aim of this project was to decipher the different sources of solutes controlling the chemical composition of the dissolved load of the rivers draining the Changjiang basin and to investigate parameters controlling the chemical weathering at the Changjiang watershed scale.<br>　　 In addition to C02(atmospheric and mainly produced in soil),other sources of acidity contributes to the dissolution of rocks, hence, we will pay particular attention to other sources of prototonsinvolved in chemical weathering reactions，especially the role of anaphoric acid in the enhancement of the weathering rates．Several studies have shown the importance of sculpture acid derived from the oxidation of pyrite at a regional scale, such as Han and Liu(2004), Up and Liu(2007) for Southwestern China and at a larger scale, such as Galy and France-Lanord (1999) for the Ganges-Brahmaputra basin, Spenee and Telmer (2005) for the Canadian Cordillera and Calmels et al.(2007) for the Mackenzie basin．In addition, sculpture envisions to the atmosphere and acidification of rain may also play a significam role in the increase of weathering rates. This reveals to be a major issue in China，despite efforts of the authorities to reduce the atrnosphcricemissions of S02．This work will allow us to ultimately estimate the CO2 consumption by rock weathering for the changjiang basin．<br>　　 Another important issue we tackled in this study is the impact of human activities on the solute concentrations of the changjiang basin rivers．Although the anthropogenic contribution to the chemical composition of the dissolved load of the Changjiang basin rivers has been demon on started in previous studies(Chen et a1.,2002 and Qin et a1.,2006)，its was not previously assessed. At last, we have analyzed the isotopic compositions of dissolved boron and tried to estimate the contribution of B derived from silicate weathering．It has been demonstrated that boron isotopes are fractionated during adsorption onto clays(Palmer et al.,1987; Spivack et al.,1987)，humicacids(Lemarchand et al.,2005; Tassel, 2006) and Fe/Mn oxides(Lemarchand et al.,2007)and that the isotopic fractionation factor was pH dependant．These experimental results highlight the potential use of boron isotopes in studies related to chemical weathering but up to now,

摘要译文

关键词：

河水地球化学; 流域化学风化; 同位素; 长江流域; 人为活动影响

学位年度：

2008

学位类型：

博士

学科专业：

环境地球化学

导师：

刘丛强

中图分类号：

P592[水地球化学]

学科分类号：

070902[地球化学];081802[地质工程]