Constraints on water chemistry by chemical weathering in the Lake Qinghai catchment, northeastern Tibetan Plateau (China): clues from Sr and its isotopic geochemistry
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Abstract
Lake water, river water, and groundwater from the Lake Qinghai catchment in the northeastern Tibetan Plateau, China have been analyzed and the results demonstrate that the chemical components and 87Sr/86Sr ratios of the waters are strictly constrained by the age and rock types of the tributaries, especially for groundwater. Dissolved ions in the Lake Qinghai catchment are derived from carbonate weathering and part from silicate sources. The chemistry of Buha River water, the largest tributary within the catchment, underlain by the late Paleozoic marine limestone and sandstones, constrains carbonate-dominated compositions of the lake water, being buffered by the waters from the other tributaries and probably by groundwater. The variation of 87Sr/86Sr ratios with cation concentrations places constraint on the Sr-isotopic compositions of the main subcatchments surrounding Lake Qinghai. The relative significance of river-water sources from different tributaries (possibly groundwater as well) in controlling the Sr distribution in Lake Qinghai provides the potential to link the influence of hydrological processes to past biological and physical parameters in the lake. The potential role of groundwater input in the water budget and chemistry of the lake emphasizes the need to further understand hydrogeological processes within the Lake Qinghai system.
Keywords
Hydrochemistry Tracer tests Groundwater flow Chemical weathering ChinaImpact de l’altération météorique sur la chimie de l’eau du bassin versant du lac Qinghai, Nord-Est du Plateau tibétain (Chine): indications fournies par Sr et ses isotopes
Résumé
Les eaux du lac, des rivières et de la nappe du bassin versant du lac Qinghai, Nord-Est du Plateau tibétain, Chine, ont été analysées; les résultats montrent que les compositions chimiques et les ratios 87Sr/86Sr de l’eau et particulièrement ceux de la nappe portent nettement la marque de la nature et de l’âge des roches de l’impluvium. Les ions du bassin d’alimentation du lac Qinghai proviennent de l’altération de roches carbonatées d’une part et de roches siliceuses d’autre part. La chimie de l’eau de la rivière Buha, le plus important tributaire du bassin sur substrat de calcaires et grès marins du paléozoique supérieur, impose une dominante carbonatée à l’eau du lac, tamponnée par l’eau des autres affluents et probablement par celle de la nappe. La corrélation des ratios 87Sr/86Sr avec les concentrations cationiques fait de Sr le marqueur isotopique du principal sous-bassin versant entourant le lac Qinghai. Le contrôle de l’apport de Sr dans le lac par les différents tributaires (incluant la nappe) montre le lien entre processus hydrogéologiques et histoires biologique et géochimique. L’importance des eaux souterraines dans la chimie et dans le bilan des apports démontre la nécessité d’une meilleure compréhension du système hydrogéologique du lac Qinghai.
Condicionamientos en la química del agua por meteorización química en la cuenca del Lago Qinghai, en el noreste de la meseta Tibetana (China): Claves a partir del Sr y su geoquímica isotópica
Resumen
Se analizaron el agua lacustre, el agua fluvial y el agua subterránea de la cuenca del Lago Qinghai en el noreste de la meseta Tibetana, China y los resultados demuestran que los componentes químicos y la relación 87Sr/86Sr de las aguas están estrictamente condicionados por la edad y tipo de rocas de los tributarios, especialmente para el aguas subterránea. Los iones disueltos en la cuenca del Lago Qinghai provienen de la meteorización de carbonatos y de parte de fuentes de silicatos. La química del agua del Río Buha, el mayor afluente dentro de la cuenca, que yace encima de las calizas y areniscas marinas del Paleozoico tardío, condiciona los compuestos mayormente carbonáticos del agua del lago, siendo am amortiguado por las agua de los otros tributarios y probablemente por el agua subterránea. La variación de la relación 87Sr/86Sr con concentraciones de cationes pone condiciones sobre las composiciones isotópicas del Sr de las principales subcuencas que rodean al lago Qinghai. La importancia relativa de las fuentes del agua del río provenientes de los distintos tributarios (posiblemente también del agua subterránea) controla la distribución del Sr, lo cual provee la capacidad de conectar la influencia de procesos hidrológicos a los parámetros biológicos y geoquímicos pasados en el lago. El rol potencial de la entrada de las aguas subterráneas en el balance de agua y la química del lago enfatizó la necesidad de entender profundamente los procesos hidrogeológicos dentro del sistema del Lago Qinghai.
青海湖流域化学风化对水化学组成的制约 : 来自Sr及其同位素地球化学的线索
摘 要
通过位于青藏高原东北缘的青海湖流域湖水、河水和地下水的化学分析结果表明, 流域内水体的化学组成和87Sr/86Sr比值主要受各河流受风化岩石的年龄和类型的严格制约, 特别是地下水的组成。青海湖流域溶解性离子主要来源于碳酸盐风化, 部分来自硅酸盐风化。作为流域内最大的河流, 布哈河的下伏围岩以晚古生代海相灰岩和砂岩为主, 其河水的化学组成控制了湖水的碱性特征, 而其他河流及地下水对湖水组成则主要起到缓冲作用。87Sr/86Sr和离子组成可以有效地定义青海湖流域内各子流域特征的水化学组成。通过各子流域的河水 (包括地下水在内) 对青海湖湖水Sr组成相对重要性的认识, 将为探讨流域水文过程对过去生物和地球化学参数的制约提供有力的线索。流域内地下水注入对湖水化学及通量的可能影响, 则需要进一步理解青海湖流域内的水文过程。
Constrangimentos à qualidade química da água em função da meteorização química na bacia do Lago Qinghai, Nordeste do Planalto Tibetano (China): inferências a partir do Sr e dos seus isótopos geoquímicos
Resumo
Constrangimentos à qualidade química da água em função da meteorização química na bacia do Lago Qinghai, Nordeste do Planalto Tibetano (China): inferências a partir do Sr e dos seus isótopos geoquímicos. A água dos lagos, dos rios, e as águas subterrâneas da bacia do Lago Qinghai, no Nordeste do Planalto Tibetano (China), foram analisadas, tendo os resultados demonstrado que as componentes químicas e o índice 87Sr/86Sr das águas são influenciados pela idade e pela composição das rochas das bacias afluentes, especialmente no que respeita às águas subterrâneas. Os iões dissolvidos na bacia afluente ao lago Qinghai são derivados de meteorização de carbonatos e também parcialmente de silicatos. A química da água do rio Buha, o maior afluente da bacia, formada por depósitos de calcários e arenitos marinhos do Paleozóico Superior, influencia a composição predominantemente carbonatada das águas do lago, a qual é tamponada pelas águas provenientes dos outros afluentes e provavelmente das águas subterrâneas. A variação do índice 87Sr/86Sr com a concentração de catiões coloca constrangimentos à composição dos isótopos de Sr das principais sub-bacias que envolvem o Lago Qinghai. A importância relativa das fontes de águas fluviais provenientes dos diversos afluentes (e possivelmente também das águas subterrâneas) no controlo da distribuição de Sr no Lago Qinghai sugere uma influência dos processos hidrológicos no passado biológico e geoquímico dos parâmetros do lago. A contribuição potencial das águas subterrâneas para o volume total e para o quimismo do lago enfatizam a necessidade de se prosseguir a análise e compreensão dos processos hidrogeológicos dos sistemas hídricos do Lago Qinghai.
Контроль химического выветривания водяной химией в бассейне озера Цинхая: Ниточки от геохимии Sr и его изотопов
РЕЗЮМЕ
Химический анализ воды озера, реки и подземных вод в бассейне озера Цинхая, находящегося на северо-восточном крае плато Цинцзана показывает, что химический состав и отношение 87Sr/86Sr воды (особенно подземной воды) строго контролируются возрастами и типами выветриванных пород, по которым текут реки. Большинство растворимых ионов в бассейне озера Цинхая происходит от выветриванных карбонатов, небольшая часть—от силикатов. В качестве наибольшой реки в бассейне озера Цинхая, река Буха течёт по поздно- палеозойскому известняку и песчанику. Химический состав воды реки Буха опрелеляет, что вода озера Цинхая обладает щёлочой характеристикой, а другие реки и подземная вода играют буферную роль для состава воды озера. Пользуя отношение 87Sr/86Sr и ионный состав, могут чётко описать химический компонент воды в бассейне озера Цинхая. Познание важности компонента стронция в речных, в том числе подземных водах, для озера Цинхая будет предоставить важные ниточки по контроли гидрографического процесса прошедшими биологическими и геохимическими параметрами. Нужно дальше изучать гидрографический процесс в бассейне озера Цинхая, чтобы пояснить возможное влияние импорта подземных вод на химию и сток воды озера.
Notes
Acknowledgements
This work has been financially supported by National Natural Science Foundation of China through grants 40599423 and 40873082, and by National Basic Research Program of China (2004CB720200). We especially thank Associate Professor Zhu Yuxin in Nanjing Institute of Geography & Limnology, Chinese Academy of Sciences, Miss Sun Yufang in Nanjing Institute of Soil Sciences, Chinese Academy of Sciences, Miss Zhang Ting in Institute of Earth Environment, Chinese Academy of Sciences, Professor Jiang Shaoyong and Mrs. Pu Wei in State Key Laboratory for Research of Mineral Deposits, Nanjing University, and Dr. Hazel Chapman in Department of Earth Sciences, University of Cambridge, for their kind help and suggestions with respect to sample analyses and laboratory work. Thanks are extended to Professor Yang Bo in Qinghai Institute of Salt Lake, Chinese Academy of Sciences for his assistance with sample collection. The manuscript greatly benefited from constructive comments by Rose Seth and an anonymous reviewer, and by Managing Editor Philippe Renard, Associate Editor Sam Earman and Technical Editorial Advisor Sue Duncan.
Supplementary material
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