Use of Sr isotopes as a tool to decipher the soil weathering processes in a tropical river catchment,southwestern India |
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| Institution: | 1. Manipal Centre for Natural Sciences (MCNS), Manipal University, Manipal 576104, India;2. Department of Civil Engineering, Manipal Institute of Technology, Manipal University, Manipal 576104, India;3. Indo-French Cell for Water Sciences, Joint IRD-IISc Laboratory, Indian Institute of Science, Bangalore 560012, India;4. GET UMR 5563, Université Paul Sabatier, IRD and CNRS, 14, avenue E. Belin, 31400 Toulouse, France;1. State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Key Laboratory of Engineering Geomechanics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;4. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;1. Department of Environmental Sciences, University of Kerala, Kariavattom, 695 581 Thiruvananthapuram, Kerala, India;2. Atmospheric Sciences Division, Centre for Earth Science Studies, PB 7250, Thiruvananthapuram 695031, India;1. Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Guangdong Institute of Eco-Environmental Science and Technology, Guangzhou, 510650, China;2. National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangzhou 510650, China;3. School of Geography and Planning, Sun Yat-sen University, Guangzhou, 510275, China;4. State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi, 830011, China;1. Géosciences Environnement Toulouse (Université de Toulouse, CNRS, IRD), 14 avenue Edouard Belin, 31400 Toulouse, France;2. Indo-French Cell for Water Sciences, Indian Institute of Science, Bangalore 560012, India;3. Centre de Recherches Hydrologiques, P.O. Box 4110, Yaoundé, Cameroon;4. INRA Agrocampus Rennes, UMR, Sol-Agronomie-Spatialisation, 65 rue de St Brieuc, 35042 Rennes, France;1. Department of Geology, University of Maryland – College Park, College Park, MD 20742, USA;2. Department of Geosciences, University of Arkansas, Fayetteville, AR 72701, USA;3. Department of Geology, Portland State University, Portland, OR 97207, USA;1. Department of Environmental Sciences, University of Kerala, Thiruvananthapuram 695 581, Kerala, India;2. Center for Environment and Development, Thiruvananthapuram 695 013, Kerala, India |
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| Abstract: | River water composition (major ion and 87Sr/86Sr ratio) was monitored on a monthly basis over a period of three years from a mountainous river (Nethravati River) of southwestern India. The total dissolved solid (TDS) concentration is relatively low (46 mg L?1) with silica being the dominant contributor. The basin is characterised by lower dissolved Sr concentration (avg. 150 nmol L?1), with radiogenic 87Sr/86Sr isotopic ratios (avg. 0.72041 at outlet). The composition of Sr and 87Sr/86Sr and their correlation with silicate derived cations in the river basin reveal that their dominant source is from the radiogenic silicate rock minerals. Their composition in the stream is controlled by a combination of physical and chemical weathering occurring in the basin. The molar ratio of SiO2/Ca and 87Sr/86Sr isotopic ratio show strong seasonal variation in the river water, i.e., low SiO2/Ca ratio with radiogenic isotopes during non-monsoon and higher SiO2/Ca with less radiogenic isotopes during monsoon season. Whereas, the seasonal variation of Rb/Sr ratio in the stream water is not significant suggesting that change in the mineral phase being involved in the weathering reaction could be unlikely for the observed molar SiO2/Ca and 87Sr/86Sr isotope variation in river water. Therefore, the shift in the stream water chemical composition could be attributed to contribution of ground water which is in contact with the bedrock (weathering front) during non-monsoon and weathering of secondary soil minerals in the regolith layer during monsoon. The secondary soil mineral weathering leads to limited silicate cation and enhanced silica fluxes in the Nethravati river basin. |
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