AUTHOR: XIANG HUANG · 2014. 1. 8. · E‐mail: xiang.huang@uef.fi Supervisors: Professor Mika Sillanpää, Dr. Tech. University of Eastern Finland Department of Environmental Science
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AUTHOR: XIANG HUANG
Water Quality in The Tibetan Plateau
Chemical Evaluation of the Headwaters of Four Major Asian Rivers
Publications of the University of Eastern Finland Dissertations in Forestry and Natural Sciences
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University of Eastern Finland Faculty of Science and Forestry
Department of Environmental Science Kuopio 2010
Kopijyvä Kuopio, 2010
Editor Prof. Pertti Pasanen Distribution:
Eastern Finland University Library / Sales of publications P.O.Box 107, FI‐80101 Joensuu, Finland
tel. +358‐50‐3058396 http://www.uef.fi/kirjasto
ISBN 978‐952‐61‐0019‐7 (Paperback); ISSNL 1798‐5668; ISSN 1798‐5668
ISBN 978‐952‐61‐0020‐3 (PDF); ISSNL 1798‐5668; ISSN 1798‐5676
Authorʹs address:
University of Eastern Finland Department of Environmental Science Laboratory of Applied Environmental Chemistry Patteristonkatu 1 FI‐50100 MIKKELI, FINLAND Tel. +358 40 355 3709 Fax +358 15 336 013 E‐mail: xiang.huang@uef.fi
Supervisors:
Professor Mika Sillanpää, Dr. Tech. University of Eastern Finland Department of Environmental Science Laboratory of Applied Environmental Chemistry Patteristonkatu 1 FI‐50100 MIKKELI, FINLAND E‐mail: mika.sillanpaa@uef.fi Professor Emeritus Egil Gjessing, Ph.D. University of Oslo Department of Chemistry P.O. Box 1033 OSLO 0315, NORWAY E‐mail: egil.gjessing@kjemi.uio.no
Reviewers:
Senior Research Scientist / Adjunct Professor, Thorjørn Larssen, Ph.D. Norwegian Institute for Water Research (NIVA) / University of Oslo NIVA address: Gaustadalléen 21, NO‐0349 OSLO, NORWAY E‐mail: thorjorn.larssen@niva.no Professor Igor M. Villa, Ph.D. University of Berne, Switzerland / University of Milan, Italy Switzerland address: Institute of Geological Sciences, Baltzerstrasse 3 3012 BERN, SWITZERLAND E‐mail: igor@geo.unibe.ch
Opponent:
Senior Lecturer Albert Galy, Dr. University of Cambridge Department of Earth Sciences Downing Street, Cambridge CAMBIRDGESHIRE, CB2 3EQ UNITED KINGDOM albert00@esc.cam.ac.uk
ABSTRACT:
Information on water quality of Asian major rivers draining Tibetan Plateau is limited, even though these rivers play a significant role in lives of more than one third of world’s population. The purpose of this study was to contribute to the knowledge of the chemical quality of these major rivers on the Plateau, to address major natural factors governing the spatial variation and to identify possible sources for contamination.
Water samples from a total of 159 sampling sites along the Yangtze River, Mekong River, Salween River, and Yarlung Tsangpo (Brahmaputra) in the Plateau were collected during spring 2006, later summer 2007 and early autumn 2008. Included in this work are also a case study of the drinking‐water quality in Lhasa city and a study of influence of a natural heavy metal enriched subsurface water and mining activity on the surface water quality in the central Tibet. Samples were subjected to a total of 34 physicochemical quality parameters, including major cations, anions, trace elements, and nutrients.
The solutes in the Tibetan rivers were dominated by Ca2+ and HCO3‐and that the dissolved matter is on average the double of that of rivers in other parts of world. Elevated concentrations of Na+, Cl‐, and SO42‐, being largely influenced by evaporites and drainage from saline lakes/geothermal waters, are a significant contributor to these high concentrations of solutes. Oxidation of sulfides is in addition an important source for the high SO42‐ in these waters. The spatial distributions of these major solutes in these waters are relatively homogenous. Multivariable analysis shows that geology and climate are the major factors governing the spatial variation. In spite of alkaline nature of these waters, the average levels of dissolved trace elements in the Tibetan rivers are high and their concentrations varied considerably. Nevertheless, the levels of Ag, Cd, Co, Cr, and Hg are negligible in all studied waters.
The headwaters of these Asian major rivers in the Plateau can be considered undisturbed. However, rapidly increased mining activities pose a high risk of heavy metal pollution for the local environment and a potential threat to the downstream water quality. Universal Decimal Classification: 502.51, 504.61, 543.33, 543.34, 556.114.6, 556.53 CAB Thesaurus: water quality; river water; rivers; Asia; Tibet; physicochemical properties; chemical composition; chemical analysis; ions; cations; anions; heavy metals; trace elements; nutrients; multivariate analysis; spatial distribution; spatial variation; geology; climate; climatic factors; climatic change; mining; contamination; water pollution
Cover picture: Yarlung Tsangpo at its headwater region, western T.A.R., Oct. 2008.
Above: Salween in Pasho, eastern T.A.R., Aug. 2009.
Right: Mekong River in Markham, eastern T.A.R., 18 Aug. 2009.
Dedicated to people I love To the Land of Snow and its rivers Over which the Sun will always shine
Acknowledgments
The research work for this PhD‐thesis was carried out at the Laboratory of Applied Environmental Chemistry in Mikkeli. I am highly grateful to Kone Foundation of Finland and the Network for University Co‐operation Tibet‐Norway in Norway for research grant. Special thanks to my home university, Tibet University for supporting me to carry out this thesis work abroad.
It is truly a difficult task for me to put my emotions into words to thank for all the help I have received from so many people during my working on this thesis. “Thank you very much” does not seem sufficient, but it is said from the bottom of my heart!
I want to express my sincere gratitude and respect to my supervisor, Professor Mika Sillanpää for he has shared his animated energy on Tibet and its water environment. My hearty appreciations to him for he has kindly provided the research funding and superb laboratory facilities and office working space. I also deeply appreciate for his encouragements during the whole course of this work. My warmest gratitude also goes to him for his constructive suggestions and comments on sampling practice during the field trips.
I am deeply grateful to my co‐supervisor, Professor Emeriti Egil Gjessing and my papers co‐author, Professor Rolf D. Vogt at the Department of Chemistry, University of Oslo (UiO), Norway for their expert advice on this work. I have always been amazed by their time efficient and detailed comments on the manuscripts. It is such a luxury experience to work on these comments and their inspirational input to the manuscripts. These experiences will be greatly beneficial to me for the years to come. My appreciations also to them for providing excellent working space for me in Oslo University at the Department of Chemistry during my short time research visiting. I am indebted also to Prof. Rolf D. Vogt for his valuable comments and revision of the English language of the thesis manuscript.
My sincere thanks are due to the official pre‐examiners of the thesis, Professor Igor M. Villa (University of Berne, Switzerland / University of Milan, Italy) and Dr. Thorjørn Larssen (Norwegian Institute for Water Research, NIVA / University of Oslo, Norway), for their encouraging and constructive comments.
I also want to express my profound appreciations to Professor Yngvar Gjessing (University of Bergen, Norway) for his endless support during my stay abroad; hosting every year Christmas Eve Party for me and my Tibetan fellows easing loneliness in these cold and dark winters. Ms Bente E. Bjørknes (University of Bergen, Norway) is warmly thanked for sharing her energetic thoughts to solve the problems in some difficult time of life. My sincere appreciations are also due to the supervisor of my Master thesis, Professor Otto Grahl‐Nielsen (University of Bergen, Norway) for his endless encouragements.
I am grateful to Professor Emeriti Hans Martin Seip at the University of Oslo, Norway; Professor Gunnhild Riise and Professor Jan Mulder at the Norwegian University of Life Sciences, Norway; Dr Marja‐Liisa Räisänen at the Finnish Geology Survey (GTK) for their insightful discussions and comments on the thesis work. Mr Håvard Hovind at the Norwegian Institute for Water Research is thanked for his advice on sampling preparation at the starting of this work; Mr Martti Pouru, Ms Sari Seppäläinen at the Mikkeli University of Applied Sciences (MAMK), Finland, and MSc (Tech.) Eveliina Repo at Laboratory of Applied Environmental Chemistry (LAEC), Kuopio University are thanked for their skillful assistances in GFAAS and ICP analyses. I want also to thanks Dr. Stanislav Rapant at the Geological Survey of Slovak Republic, and Professor Kang Shichang, Professor Zhu Liping and their research group at the Institute of Tibetan Plateau Research, Chinese Academy of Sciences for the useful discussions. My thanks are also conveyed to the articles co‐author senior assistant Sirpa Peräniemi at the Department of Biosciences, University of Kuopio.
Many thanks go to my friends in Tibet for being, at one time or another, with me on the phone during my stay abroad. Special credit goes to my dear friends Yangzom and Tseyang for their efforts making the sampling trips in Tibet possible. I am also
thankful to my colleagues at LAEC and my friends in Finland. People come and people go, yet the link remains and finally comes my time to leave. Special thanks to Heikki Särkkä for his endless help in my stay in Mikkeli.
My hearty thanks to my mother, Lhadroma, and my late father for their understanding and endless love, which have blessed me throughout my whole life. My large family is thanked for taking care of my children during my leave for working abroad. Special thanks to Lhagchong for her sacrifice and taking care of my family. My unlimited appreciation goes to Pasang for his loving supports and encouragements during all these years. Finally, my dearest two daughters, Dezhun‐la and Pemu, I can not ask them for understanding of being away from them for years, but they are thanked for being an inspiration of my hard research life and they are loved by my soul! Mikkeli, November 2009
Huang Xiang
Abbreviations
a.s.l. above sea level AAS Atomic Absorption Spectrometry BG Borosilicate Glass CV ‐ AFS Cold Vapor‐ Atomic Fluorescence Spectrometry DOM Dissolved Organic Matter EC Electrical Conductivity FI ‐ AAS Flow Injection – Atomic Absorption Spectrometry GB Chinese National Standards GFAAS Graphite Furnace Atomic Absorption
Spectrometry HF High Flow HPLC High Performance Liquid Chromatography IC Ion Chromatography ICP Inductively Coupled Plasma ICP ‐ AES Inductively Coupled Plasma – Atomic Emission
Spectrometry ICP ‐ OES Inductively Coupled Plasma – Optical Emission
Spectrometry LF Low Flow LOD Limit of Detection LOQ Limit of Quantification LSI Langelier Saturation Index MEP Ministry of Environmental Protection of the
People’s Republic of China MOH Ministry of Health of the People’s Republic of
China MOH & SAC Ministry of Health of the People’s Republic of
China & Standardization Administration of the People’s Republic of China
PC Principal Component PCA Principal Component Analysis PE Polyethylene PMB Phosphormolybdenum Blue PP Polypropylene QPs Quality Parameters
RSI Ryznar Stability Index SEPA State Environment Protection Administration of
the People’s Republic of China SM Suspended Material St. Sampling Site T.A.R. Tibet Autonomous Region TDN Total Dissolved Nitrogen TDP Total Dissolved Phosphorus TDS Total Dissolved Solid TPRWHS Three Parallel River World Heritage Site WHO World Health Organization
LIST OF ORIGINAL PUBLICATIONS
This thesis consists of a summarizing review including some unpublished data and the following original research papers, which are referred to in the text by their respective Roman numbers given below.
I Huang, X., Sillanpää, M., Bu‐duo & Gjessing, E.T., 2008. Water quality in the Tibetan Plateau: metal contents of four selected rivers. Environmental Pollution, 156 (2), pp.270‐277.
II Huang, X., Sillanpää, M., Gjessing, E.T. & Vogt, R.D., 2009.
Water quality in the Tibetan Plateau: major ions and trace elements in the headwaters of four major Asian rivers. Science of the Total Environment, 407 (24), pp.6242‐6254.
III Huang, X., Sillanpää, M., Gjessing, E.T., Peräniemi, S. & Vogt,
R.D., 2010. Water quality in the Southern Tibetan Plateau: chemical evaluation of the Yarlung Tsangpo (Brahmaputra). River Research and Applications, In Press. DOI: 10.1002/rra.1332.
IV Huang, X., Sillanpää, M., Gjessing, E.T., Peräniemi, S. & Vogt,
R.D., 2010. Environmental risk assessment of mining activities on the surface water quality in Tibet: Gyama valley. Under review.
Contents
1. Introduction....................................................................................... 19 2. Study background ............................................................................. 21 2.1 WATER RESOURCES OF THE TIBETAN PLATEAU .............. 21 2.2 WATER QUALITY ASSESSMENTS IN THE TIBETAN
PLATEAU ....................................................................................... 22 2.3 CONTROLLING FACTORS OF WATER QUALITY IN THE
TIBETAN PLATEAU..................................................................... 24 2.3.1 Natural processes ‐ weathering and erosion................................. 24 2.3.2 Mining activities .......................................................................... 24 2.3.3 Municipal wastes.......................................................................... 25 2.3.4 Climate changes............................................................................ 26 2.4 GEOLOGY AND CLIMATIC ENVIRONMENT OF THE
TIBETAN PLATEAU..................................................................... 26 2.5 MAJOR RIVER CATCHMENTS .................................................. 28 2.5.1 Yangtze River ............................................................................... 28 2.5.2 Mekong River ............................................................................... 29 2.5.3 Salween River ............................................................................... 30 2.5.4 Yarlung Tsangpo.......................................................................... 31 2.6 WATER QUALITY GUIDELINES ............................................... 32 2.6.1 WHO guidelines........................................................................... 32 2.6.2 China’s standards ......................................................................... 33 3. Objectives of this study ................................................................... 35 4. Materials and methods .................................................................... 37 4.1 SAMPLING PROCEDURE ........................................................... 37 4.2 SAMPLE HANDLING AND PRESERVATION ........................ 38 4.3 IN‐SITU MEASUREMENTS ......................................................... 39 4.4 LABORATORY ANALYSES......................................................... 39 4.4.1 Major cations and trace elements ................................................. 39 4.4.2 Mercury........................................................................................ 40 4.4.3 Anions and NH4+.......................................................................... 41 4.4.4 Total dissolved sulfur ................................................................... 41 4.4.5 TDP, TDN and silica ................................................................... 41
4.5 STATISTIC METHODS AND DATA ANALYSIS ..................... 42 5. Results and discussion ..................................................................... 45 5.1 DATA COLLECTION.................................................................... 45 5.2 WATER CHEMISTRY OF THE TIBETAN RIVERS ................... 45 5.3 RIVER WATER QUALITY............................................................ 51 5.3.1 Yangtze River ............................................................................... 51 5.3.2 Mekong River ............................................................................... 52 5.3.3 Salween River ............................................................................... 53 5.3.4 Yarlung Tsangpo.......................................................................... 53 5.4 MAJOR CONTROLLING FACTORS OF THE TIBETAN RIVER
CHEMISTRY................................................................................... 54 5.5 DRINKING WATER QUALITY – A CASE STUDY IN LHASA
CITY ................................................................................................. 56 5.6 MINING IMPACT ON THE SURFACE WATER QUALITY – A
CASE STUDY IN GYAMA VALLEY........................................... 57 6. Conclusions and further research ................................................... 59 7. References ........................................................................................... 63 8. Appendices ......................................................................................... 69
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1. Introduction
The Tibetan Plateau is called the “Water Tower of Asia” as it is the source of the eight largest rivers in Asia. These rivers have perennial flow throughout the year and operate as essential lifeline of the people on the Plateau and the downstream nations. Access to adequate amount and quality of water is a major limiting factor for the development in many parts of these countries (Kruawal, et al., 2005; Shinkai, et al., 2007).
In spite of these rivers’ significance, knowledge and understanding of the water quality of these water resources are limited. This is partially because of the environment in the Tibetan Plateau has traditionally been considered pristine. In addition, limited accessibility to these rivers and their tributaries in this high mountain range of the Plateau has led to a restricted number of studies on the rivers. There is growing public concern about the potential effects of rapid economic development and demographic changes on the Plateau’s fragile environment (e.g. Lin, et al., 2007, p. 240; Sun, 2007). One of these major concerns is related to the potential impact of the rapidly increased mining activities on the Plateau’s ecosystem (Lin, et al., 2007). Furthermore, there is a concern to the effect of climate change (global warming) and the resulting changes in hydrological conditions on the availability of the water from the Plateau (Barnett, et al., 2005; Chen, et al., 2007; Immerzeel, 2007). As weathering and erosion in the Plateau is related to the climatic condition (Liu, et al., 2005; Tipper, et al., 2006a), climate change may also play a significant role in controlling major chemical fluxes of the rivers draining the Tibetan Plateau. In order to assess future changes in the water quality, due especially to the increasing mining activity and urbanization, it is important to conduct a systematic assessment to establish a chemical database of quality state of these rivers. Furthermore, in order to predict effects of a changing environment on the water
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quality there is a need to assess the main factors governing spatial and temporal variation in water chemistry.
In this work, water quality of the headwaters of four major Asian rivers, i.e. the Yangtze River, the Mekong River, the Salween River and the Yarlung Tsangpo (Brahmaputra) draining the Tibetan Plateau was disclosed and evaluated, and major factors controlling the chemistry of these waters were identified (Papers I‐III). An assessment of potential impact of mining activities on the regional surface water quality in the central Tibet was also conducted (Paper IV). A simple evaluation of the drinking‐water quality in the largest city of the Plateau, Lhasa, the capital city of the Tibet Autonomous Region (T.A.R.), is included (supplementary data in the thesis summary). The results presented here provide new information on the current chemical characteristics of surface water and drinking‐water in the “Water Tower of Asia” and offer background and reference for future studies.
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2. Study background
2.1 WATER RESOURCES OF THE TIBETAN PLATEAU
Within the Tibetan Plateau there are more than 100 rivers that have catchments area larger than 2 000 km2, and there are 20 rivers that have drainage areas above 10 000 km2 (Guan & Chen, 1980; He & Feng, 1996). The Plateau is called the “Water Tower of Asia” as it is the source for the eight largest rivers in Asia: 1. The Huang He, 2. The Yangtze River, 3. The Mekong River, 4. The Salween River, 5. The Irrawaddy, 6. The Brahmaputra (Yarlung Tsangpo), 7. The Ganges, and 8. The Indus (Figure 1). These eight rivers are among the 25 largest rivers in the world (Meade, 1996), flowing through to the most populous regions on earth, constituting the water sources for about one third of the world’s population.
5. Irrawaddy
1. Huan
g He
8. Indus
7. Ganges
1 000 miles
Tibetan Plateau
2.Yangtze River• April-May 2006• Aug.-Sep. 2007• 36 sampling sites• Main stream: > 800 km
3. Mekong River• April-May 2006• Aug.-Sep. 2007• 21 sampling sites• Main stream: > 500 km
4. Salween River• April-May 2006• Aug.-Sep. 2007• 17 sampling sites• Main stream: < 20 km
6. Yarlung Tsangpo • April-May 2006• Aug.-Sep. 2007• Sep.-Oct. 2008• 85 sampling sites• Main stream: > 1600 km©2009 Microsoft Corporation ©2009 NAVTEQ
5. Irrawaddy
1. Huan
g He
8. Indus
7. Ganges
1 000 miles
Tibetan Plateau
2.Yangtze River• April-May 2006• Aug.-Sep. 2007• 36 sampling sites• Main stream: > 800 km
3. Mekong River• April-May 2006• Aug.-Sep. 2007• 21 sampling sites• Main stream: > 500 km
4. Salween River• April-May 2006• Aug.-Sep. 2007• 17 sampling sites• Main stream: < 20 km
6. Yarlung Tsangpo • April-May 2006• Aug.-Sep. 2007• Sep.-Oct. 2008• 85 sampling sites• Main stream: > 1600 km©2009 Microsoft Corporation ©2009 NAVTEQ
Figure 1: The eight largest Asian rivers originating from the Tibetan Plateau. Sampling information of the four rivers studied in the present work is listed at the right.
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The Tibetan Plateau is also endowed with more than 1 600 natural lakes with surface area above 1 km2 and almost 40 lakes of area larger than 50 km2. There are five lakes having a surface area above 1 000 km2. Notably, more than 350 are saline lakes of various types, representing 42% of the total area of lakes in the Plateau, with salinities from less than 3 to over 500 parts per thousand (Zheng, 1997, p. xiii). These saline lakes are of great interest for both scientific research and economic development owing to their unique and abundant mineral resources.
2.2 WATER QUALITY ASSESSMENTS IN THE TIBETAN PLATEAU
There is very little information available on the chemical properties of these world’s large rivers draining the Tibetan Plateau. This is mainly because of limited accessibility to these rivers and that the Plateau’s environment has traditionally been considered as pristine. On the other hand, the quality of these rivers downstream from the Plateau has received attention, to various degrees, due to severe deterioration of the water quality relating to the large population and rapid economic development in the downstream countries.
To the south in India, 70% of surface water resources and a growing percentage of groundwater reserves are contaminated by organic and inorganic micropollutants and microorganisms. These pollutions are mainly due to discharge of untreated municipal and industrial wastes (Girija, et al., 2007; MoEF, 2009; Goldar & Banerjee, 2004). A number of studies have shown that discharges of untreated wastewater into the large rivers in India are also responsible for heavy metal contaminations in both the river water and bed sediments (Purushothaman & Chakrapani, 2007; Singh, V.K., et al., 2005). In spite of the severe water problems in the country, the water quality monitoring program seems not to be followed up satisfactorily (Goldar & Banerjee, 2004 and references therein). In addition, unsafe groundwater, with detrimental concentrations of F‐ and As, poses a great risk for more than 80 million people in the country (MoEF, 2009).
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To the east in China, despite sophisticated surface water monitoring program (consists of 109 quality control parameters) and environmental standards, currently 90 million people have no access to clean drinking water (Li, 2009) and about 50% of country’s major river watersheds are severely polluted by domestic and industrial effluents. A total of 557 billion tones of municipal wastes and industrial wastewater were generated nationwide in 2007 (MEP, 2008), amongst, 57% of that was discharged into the Yangtze River basin alone. This has led to about 15% of the water in this river basin has a quality that fails to reach the criteria of the lowest water grade (V Grade) (CWRC, 2008). Recent measurements of some trace elements (As, Pb, Cd, Cr, Cu, Ni, Hg and Zn) in the middle and lower reaches of the Yangtze river, showed that all these elements, in both their dissolved and particulate phases had a higher concentrations today than estimates made 20 years ago (Müller, et al., 2008; Zhang, 1995).
Water pollution is also one of the most critical environmental problems in the countries downstream from the Plateau and access to adequate water is a major limiting factor for development in many parts of these countries (Kruawal, et al., 2005; Shinkai, et al., 2007). The quality statue of the runoff water from the Tibetan Plateau to the downstream areas is therefore significant.
One of the earliest studies on water chemistry of the rivers draining in the Tibetan Plateau was by Hu, et al. (1982). This publication, however, based on four samples from the Yarlung Tsangpo and its tributaries near Lhasa, included only information on major ions (i.e. Na+, K+, Mg2+, Ca2+, Cl‐, and SO42‐) and silicon. Since then a number of studies on the Yarlung Tsangpo and other major rivers have been conducted both at the Plateau and downstream (Chetelat, et al., 2008; Galy & France‐Lanord, 1999; Hren, et al., 2007; Singh, S.K., et al., 2005; Wu, et al. 2008a, 2008b). However, these have also focused on contributing knowledge of major ion composition and related to weathering/erosion processes in the river catchments and to the sediment transportation.
To date, a systematic assessment of the effect of natural process as well as the present anthropogenic factors governing the water quality in the Plateau has not been conducted. In fact, the present
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chemical state of these major Asian rivers draining the Tibetan Plateau is not yet defined. This lack of knowledge is compelling considering these rivers’ major role as the water sources for most of Asia’s population. This makes it urgent to establish a database showing the present quality of these enormous water resources as a reference for future changes.
2.3 CONTROLLING FACTORS OF WATER QUALITY IN THE
TIBETAN PLATEAU
2.3.1 Natural processes ‐ weathering and erosion The Himalayan region has a high rate of weathering and erosion (e.g. Hren, et al., 2007; Singh, S.K., et al., 2005). An early estimation has stated that half the world’s river sediment is derived from the Himalayan region and its environs (Meade, 1996), owing to the unique tectonic uplift feature of the Plateau and steep slopes along the river courses. In relatively undisturbed continental environments, the surface water chemistry is to a large extent reflected by the soil constituents in the catchments. Soils on the Plateau are weakly developed and the content of soil organic matter is scarce (Zhang, et al., 2002). Weathering and erosion of the soil parent materials, as well as the underlying lithologies within the river catchments, provide, therefore, a key contribution to the chemical loading of these Tibetan waters (e.g. Hren, et al., 2007; Singh, S.K., et al., 2005; Tian, et al., 1993; Wu, et al., 2008b; Zhang, et al., 2002).
2.3.2 Mining activities The Tibetan Plateau is further renowned for its large ore resources. Beginning from early 1950s, several large mineral deposit belts and over 100 sorts of mineral resources, including over 45% of China’s chromite deposit and significant deposition of copper, lithium, iron, boron and gold have been identified in the region (Lin, et al., 2007, p. 21‐69). Amongst these, in the central Tibet along the northern bank of the Yarlung Tsangpo, the Gandise porphyry copper belt (600 km × 120 km) is believed to be one of the three
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largest porphyry belts in the world (Zheng, et al., 2007). The Plateau is furthermore believed to have a significant potential for further future discoveries of large mineral deposits, since the Plateau’s geological history is favorable for mineralization (Zheng, et al., 2007; Zhong, 2002). Encouraged by the convenience of the newly operated railway, in addition to accelerating economic growth in Tibet and the general supply shortage in whole China, the mining industry in the Plateau has received high priority and, hence, started playing significant role in the regional industrial development.
Mining and its waste disposal is an important environmental threat worldwide. Nearly 20 years of industrial scale mining operations have been carried out on the Plateau. The ongoing operations are lacking adequate management and operating experience causing poor planning and waste management (Lin et al., 2007). Furthermore, since environmental regulations are poorly implemented over the Plateau, there is also a lack of knowledge on the apparent and potential impact of these mining activities on the environment. This is of particular concern with regards to the Plateau’s vast supply of freshwater. Accelerated with the established central China‐Tibet railway, large scale mining operations are launched and more are to come on the Plateau. Mineral processing factories are located within the major river catchments in the Plateau. Apparently, the huge amounts of mining wastes that are generated by these activities pose a significant threat to the region’s surface water and the fragile environment.
2.3.3 Municipal wastes The Tibetan Plateau, within the T.A.R. hosts a population of 2,840,000. In spite of that the majority of this population is concentrated within the major river basins; no municipal waste treatment facility exists in the region. Municipal wastes have traditionally been dumped into the rivers and solid waste is piled in landfills near the settlements without adequate management. Studies on the characteristics of municipal wastes, landfill leachate and proper disposal and treatment in the region are limited (Jiang,
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et al., 2009). Along with the rapid economic development and dramatic demographic change in the region, Jiang and co‐workers (2009) estimated that the total municipal solid waste generation in 2020 in T.A.R. will be 37% higher than that in 2006. This will pose an additional threat to the quality of water in the Plateau.
2.3.4 Climate changes Climate change is well documented to have a negative effect on seasonal water availability on the Tibetan Plateau (Barnett, et al., 2005; Chen, X.P., et al., 2001; Chen, Z.Y., et al., 2001a; Guo, et al., 2007; Immerzeel, 2007). It is also a potential threat to the water quality, because it affects the intensity of weathering/erosion in the river basins (Liu, et al., 2005; Tipper, et al., 2006a). Meteorological studies have demonstrated that over the past 40 years the climate in most part of the Tibetan Plateau is changing from cold and dry to warmer and more moist weather conditions (Du, 2001; Du & Ma, 2004; You, et al., 2007). The air temperature increase over the Plateau is higher than in other parts of the world (Du, 2001; Du, et al., 2004). This increased air temperature is, in particular, pronounced in the major river basins on the Plateau (You, et al., 2007; Wang, et al., 2001). While the mean annual precipitation (from 1770s to 1990s) has increased at a rate of about 20 mm per decade (Du & Ma, 2004; Zhang & Tang, 2000) in these river basins. Climate change together with land‐use changes and degradation of grassland on the Plateau are major factors affecting the intensity of the weathering and erosion (Wang, et al., 2007; Zhang, et al., 2007). These factors are consequently of importance for the chemical quality of the water.
2.4 GEOLOGY AND CLIMATIC ENVIRONMENT OF THE TIBETAN
PLATEAU
The Tibetan Plateau covers an area of 2.4 million km2. It is renowned for its numerous high mountains, with the Kunlun Mountains in the north, the Tanggulha Mountains in the northeast, the Hengduan Mountains in the east, the Gangdies Mountains and
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the Nyenchentangla Mountains stretching from the west across centre towards southeast, and finally the famous Himalayas on far south margin of the Plateau. The Plateau has an average elevation of more than 4 000 m above sea level (a.s.l.), gradually sloping from the northwest downwards to the southeast. This is coincident with the typical weather type on the Plateau that gradually varies from arid to semi‐arid in the upper northwest to the central part of the Plateau, to subtropics in the lower southeast part of the Plateau. The dominant vegetation along the same gradient are alpine creeping dwarf semi‐shrubby sand‐gravelly deserts, alpine steppes, alpine meadows, and subtropical forest, respectively (ISSAS, 1986).
The Southeast and Southwest monsoon, with abundant moisture and high temperature, sweeps up into the region through the major valleys at the east and southeast margins of the Plateau. However, the west and northwest parts of the Plateau are shielded by the high mountains (Shi & Yang, 1985) and are mainly dominated by the continental recycling and the westerlies (Yao, et al., 2008). Mean annual air temperature of the Plateau differs from ‐2.9 °C in the northwest to 11.9 °C in the southeast, and mean annual diurnal temperature varies from 17.5 °C in the north to 10.0 °C in the south. The mean annual precipitation varies from 74 mm in the northwest to 802 mm in the southeast. This uneven distribution of precipitation is due to both the impact of the monsoons and the topography. More than 80% of the rain falls between May and September (ECLCT, 2005). The Plateau is subjected to a high amount of solar radiation compared to other regions at the same latitude. Annual total amount of global radiation is in the range of 4 000 to 8 000 MJ/m2 and annual sunshine duration is between 1 500 and 3 500 h on the Plateau. This causes evaporation to significantly exceed rainfall on the Plateau. The annual total evaporation varies from 2 800 mm to 1 186 mm from the northwest to the southeast part of the Plateau (ECLCT, 2005).
The combination of the indeed complex topography and the nature of the monsoonal climate has also endowed the Plateau with both large continental and monsoon maritime mountain glaciers (Shi & Yang, 1985). In terms of mass, this is then the third largest ice cover on earth (Barnett, et al., 2005). The distribution of
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these numerous mountain glaciers is of great significance to the water resources.
2.5 MAJOR RIVER CATCHMENTS
In this work, water quality in the headwaters of four major Asian rivers draining in the Tibetan Plateau has been studied. These four rivers, from the eastern margin of the Plateau to the southern Plateau, are: the Yangtze River, the Mekong River, the Salween River and the Yarlung Tsangpo (Brahmaputra) (Figure 1). Details on these rivers are described below.
2.5.1 Yangtze River The Yangtze River is known as the Changjiang (the long river) in China and Drichu in Tibetan. The river upper reaches in the Tibetan Plateau and downstream including the stretch through Sichuan are referred as Jinsha‐Jiang in Chinese. It is the longest river in Asia and the third longest in the world. It ranks fourth in the world in terms of total water discharge to the sea (Chen, et al., 2002; Chen, Z.Y., et al., 2001b). Yangtze River drains nearly 20% of China, and nearly 10% of the world’s population is living within its river basin (Meade, 1996). The river starts from the Geladandong glacier (more than 6 000 m a.s.l.) at the Tanggulha Mountains and flows first southwards on the Tibetan Plateau, then north and northeast, and finally east until it runs out in the East China Sea of the Pacific Ocean. The importance of the Yangtze River is not only because of its size, but also due to the significant role that the river plays in the historical and socioeconomic development of China.
The river source area lies close to the transition zone between alpine steppes and the arid region to the north and west. Of strong significance to the water chemistry is the dominance of evaporite‐bearing Quaternary fluvial deposits, clastic rocks and limestones bedrocks in the upper part of the catchments (Chen, et al., 2002; Hu, et al., 1982; Wu, et al., 2008a, 2008b). Along the river down to Shigu town in west Yunnan the river basin is comprised of low‐grade metamorphic rocks, clastic rocks, intermediate‐basic volcanic
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rocks, granitoid intrusive rocks and some fractions of ophiolitic melanges (ISSAS, 1986; Wu, et al., 2008b). In the river catchments above Shigu town, the mean annual precipitation is about 470 mm (CWRC, 2008), though more important is that the annual evaporation loss is two to six times higher than annual precipitation (Zheng, 1997, p. 55). The vegetation types in most of the Yangtze River basin on the Plateau are alpine meadow, alpine shrub and forest.
The Yangtze River is fed by a number of large tributaries. The Yalong River (1640 km long and draining 128 000 km2 in area) is the largest contributor to the main river in its headwaters region. It causes the water discharge of the Yangtze River to double downstream of Panzhihua, one of the heaviest industrialized cities in Sichuan Province, where it merges into the main river. The source area of this tributary is composed of clastic‐ and, volcanic rocks overlain by Quaternary deposits, while ophiolites, granites and volcanic rocks are exposed along the upstream and middle reaches of the river (Wu, et al., 2008a).
2.5.2 Mekong River Mekong River is known as Lancang‐jiang in China and Dzachu in Tibetan. It is the 12th longest river in the world and the 7th longest river in Asia. It is ranked 8th in terms of mean water discharge (Gupta, 2007). Although the actual source of the river, in the eastern Plateau at an elevation of over 5 000 m a.s.l., is still under debate (Zhou, et al., 1996; Zhou & Guan, 2001), the headwaters of Mekong river bare the name Dzachu (river of rock) in Tibetan, reflecting the river’s appearance. Another headwater to Mekong is the Ngomchu. The Dzachu and Ngomchu are some 518 km and 364 km long, respectively, and merge in Chamdo county town into the Mekong River (Lanchang‐jiang) (Chamdo in Tibetan means “join of water”). From its sources, the Mekong River flows on rock in a steep narrow valley for nearly 80% of its length (Gupta, 2007) and finally ends up in the South China Sea of the Pacific Ocean. As the majority of the catchments of Mekong River are on the Plateau, the watershed is mainly located within the semi‐arid monsoon climate zone. The dominant forms of vegetation are alpine steppes and
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meadows in the north, and alpine shrub and subtropical forests in the south (ISSAS, 1986). Low‐grade metamorphic rocks, granitoid intrusive rocks, clastic rocks and limestones are exposed in the river catchment from Chamdo along most of the river course on the Plateau. The headwater catchment is clastic rocks, limestones and volcanic rocks (ISSAS, 1986; Wu, et al., 2008a).
The Mekong River is closely bounded by the Salween River to the west and the Yangtze River to the east (Figure 1). These three rivers run in parallel in the south‐eastern Plateau to the west of Yunnan Province of China, where they form the Three Parallel Rivers World Heritage Site (TPRWHS), which is known to be one of the ecologically richest temperate regions of the world. The river downstream from China flows through Myanmar (Burma), Lao PDR, Thailand, Cambodia and Vietnam. At the low reaches of the river, the fishery of the river basin is one of the most productive in the world, owing also high diversity of fishery resources (Coates, et al., 2003).
2.5.3 Salween River Salween River is known as Nu‐jiang in China and Nakchu or Gyalmo Ngulchu in Tibetan. It is the second longest river in Southeast Asia and it is one of only two remaining large non‐regulated rivers in China. The river originates from the northern Tibetan Plateau and ends up in its delta at the Andaman Sea of the Indian Ocean. While the river source area is dominated by rather poor alpine steppes, alpine meadows and arid shrubs, the river runs through a very lush ecologically diverse region at its low reach in the TPRWHS area in western Yunnan province of China. The river drains a vast, flat alpine grassland at its source area. However, it virtually has no floodplain along most of its length and runs instead through deep narrow gorges (Bird, et al., 2008). The upstream river basin consists of a very mixed geology with low‐grade metamorphic rocks, granitoid intrusive rocks, Paleozoic clastic rocks and notably some limestones. The soils in the head source area consist of Quaternary fluvial deposits and small portion of ophiolitic and undivided ultrabasic rocks (ISSAS, 1986; Wu, et al., 2008a). The Yuchu is the largest contributor to the Salween River on the Plateau. It runs
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parallel to the Salween River through the vast Pomda pasture until they merge.
2.5.4 Yarlung Tsangpo Yarlung Tsangpo (Tsangpo in Tibetan means large river) is known as Brahmaputra downstream in India. It is the largest river both in terms of length and drainage areas at the northern slopes of the Himalayan ranges on the southern Tibetan Plateau (Guan & Chen, 1980). Yarlung Tsangpo is the only major river with an East‐West course in the region, and it remains as the second non‐regulated large river left in China. It starts at the Jemayangdrung glacier near Mount Kailash, at an elevation above 5 200 m a.s.l., in the south‐west and runs through the Gandise ‐ Himalayan Tectonic Region in the southern Plateau (Figure1). The uppermost reaches of the river, known as Dachok Tsangpo, run some 270 km through nomadic sandy pastures. Further downstream, along most of its length (~1 300 km) it shifts between running through narrow gorges and wide open fluvial valleys. On route it passes through some of the most fertile plains and major cities and towns on the Plateau. Along its lower reaches in Tibet the river runs some 500 km through deep canyons in a densely forested area. At the easternmost part of the Himalayas the river turns southwards and finally flows into the Bay of Bengal of the Indian Ocean.
As can be inferred from above, the southern Tibetan Plateau is generally dominated by Palaeozoic‐Mesozoic carbonate and clastic sedimentary rocks (Galy & France‐Lanord, 1999). Though the bedrock in the Yarlung Tsangpo river basin on the Plateau consists mainly of igneous granite/granitic gneiss, schist/other felsic volcanic and mafic volcanic rock, some sedimentary and metamorphosed sedimentary units (including silt, clay and sandstone units) exists. In other words, little or no carbonate rocks are found in the upper and middle parts of the catchments (Hren, et al., 2007). Rock outcrops of ophiolites and ophiolitic melanges are commonly found along the entire river course (GMRT, 1993). Evaporites can be found throughout the watershed (Hu, et al., 1982 and reference therein).
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The Yarlung Tsangpo has five major tributaries with a drainage area larger than 10 000 km2 (Guan & Chen, 1980; Liu, 1999). Lhasa River (Kyichu), Nyangchu (Ch: Nianchu He) and Raga Tsangpo (Dokzhung Tsangpo) are the major contributing streams in the upper and middle reaches of the river. Parlung Tsangpo and Nyangchu (Ch: Nyiyang He) are the major tributaries in the lower reaches of the river in the Plateau. Of these the Parlung Tsangpo is the largest contributor in terms of water discharge to the Yarlung Tsangpo (Guan & Chen, 1980), while the Lhasa River, draining an area of 32 471 km2, has the largest catchments (He & Feng, 1996).
The Yarlung Tsangpo valley is the historical, cultural, economic and political centre of Tibet. More than half of the population in this region is living in the valley and the river and its tributaries supply the main agriculture region on the Plateau with water. The rapid economic development in Tibet has also been centered within the river catchments.
2.6 WATER QUALITY GUIDELINES
River water in the most part of the Tibetan Plateau serves as the drinking water sources for the public. Chemical quality of the headwaters of the four major rivers were, therefore, evaluated against the criteria of the World Health Organization (WHO) guidelines for drinking‐water quality and Chinese national standards for drinking water quality and surface water quality (first two grades, suitable as source for drinking water).
2.6.1 WHO guidelines WHO Guidelines for Drinking‐water Quality are generally adopted worldwide for water quality assessment and management. The third edition (WHO, 2004) of the guidelines included 125 chemical quality parameters. Among these 21 are considered in the present study (Appendix I).
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2.6.2 China’s standards Standards for Drinking Water Quality (GB 5749) were established by the Ministry of Health (MOH) in China for the first time in 1985. The first revision of this standard was made in 2006. The standard is addressed to regulate the water quality for drinking water both from central water supply, and small/non‐central water supply. According to this standard, a total of 38 quality parameters, mainly inorganic chemicals, are categorized as regular indices, indicating a general state of drinking water quality. Among them, a total of 16 (i.e. As, Cd, Cr(VI), Pb, Hg, F‐, NO3‐(N), pH, Al, Fe, Mn, Cu, Zn, Cl‐, SO42‐, and TDS) were considered in the present study (Appendix I). Environmental Quality Standards for Surface Water (GB 3838) were
established in 1983 by the Ministry of Environmental Protection (MEP) in China (former SEPA: State Environmental Protection Administration of the P.R. China). The present edition (GB 3838‐2002) is the third revision made in 2002. The standard categorizes surface water into five grades according to different ecosystem services of surface water: Grade I: Headwaters and national nature reserves; Grade II: First level preservation areas for central supply drinking water sources; habitats of rare aquatic life; spawning zones for fish and shrimps; Grade III: Second level reservation areas for drinking water sources; reservation zones for fishes; swimming areas; Grade IV: General industrial water supply; recreational waters in which there is no direct human contacts with the water; Grade V: Agricultural water supply and general landscape.
A total of 24 quality parameters, including water temperature, pH, NH3‐N, Total‐P, Total‐N, Cu, Zn, F‐, As, Hg, Cd, Cr, and Pb measured in the present study, are listed as fundamental requirement for the assessment of all grades of water quality. In additions, 85 parameters (e.g. SO42‐, Cl‐, NO3‐, Fe, Mn, Mo, Co, Ni, and Ti) are required for quality control of surface water used as water source for central drinking water supply. In general, Grades I and II are considered potable. Since surface waters at the Plateau, with few exceptions (e.g. in Lhasa City), are commonly used as drinking water in the region, the stream water quality in the
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Tibetan Plateau has been assessed mainly based on the criteria for these two grades. Details on the risk limits from these standards are listed in Appendix I.
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3. Objectives of this study
This thesis is the first systematic study on chemical evaluation of the water quality of the “Water Tower of Asia”. The overall objective of this work was to contribute to defining the present chemical quality of these headwaters in the Tibetan Plateau, and to increase the knowledge about detrimental environmental degradation caused by the rapid economic development on the abundant fresh water resources on the Tibetan Plateau. Specifically, the aims were: 1. To assess temporal and spatial variations of chemical
compositions of the headwaters of four major Asian rivers, i.e. the Yangtze River, the Mekong River, the Salween River and the Yarlung Tsangpo in the Tibetan Plateau (Papers I‐IV);
2. To address possible mechanisms governing the spatial variation of the water chemical compositions in these rivers (Papers II and III);
3. To identify potential sources of contaminants (Papers I‐IV); 4. To evaluate the present chemical quality of the drinking water
and identify potential sources for contaminations (supplement unpublished data);
5. To assess the present and future potential risks of the mining operations on the stream water quality and to the downstream aquatic environment (Paper IV).
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4. Materials and methods
4.1 SAMPLING PROCEDURE
A systematic water quality study is presented in this thesis. Temporal variation was assessed by collecting water samples before the rain season (in April‐May) and after the heavy rain season (in Aug.‐Sep.). The study of spatial variation was performed by collecting water samples at the Tibetan Plateau along the Yangtze River, Mekong River, Salween River and Yarlung Tsangpo river courses in T.A.R., Sichuan Province, and Yunnan Province of China. Sampling sites (St.), located both in remote and urban areas were selected with the aim to cover the water course of the four main rivers and their major tributaries. Water flowing through major cities and towns was covered by the sampling program to evaluate the potential urban impact. An important selection criterion was also to obtain samples which could be compared to earlier studies. Water samples were collected approximately 30 cm below the water surface and from the main water masses of the stream.
Samples from mining sites within the Yarlung Tsangpo river catchments and drinking water (groundwater supplied) samples from the capital city of T.A.R., Lhasa, were also collected. For details on each year’s surface water sampling stations and protocols see Papers I‐IV. Sampling of suspended materials (SM) with a hand vacuum pump filtration system was prepared. However, the actual sampling was not possible due to the low atmospheric pressure on the Plateau. A portable filtration system that works properly at high elevation (above 4 000 m a.s.l.) for collecting of SM samples would be needed for future especially in remote areas.
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4.2 SAMPLE HANDLING AND PRESERVATION
Sample handling and preservation were carried out with considerations of both the guidance of international/national standards (ISO, 1985; SEPA, 1991) and the requirements of the applied analytical methods. A two liter colorless polypropylene plastic (PP) bottle was used for water sample collection; A 15 mL colorless PP bottle with polyethylene (PE) plastic screw cap was used for storing sample fraction for metal ions measurements; A colorless 100 mL PP/PE bottle (deionized water pre‐washed) with PE screw cap was applied for collecting sample for anion and other parameter measurements; A 16 × 125 mm size colorless borosilicate glass (BG) bottle with a Teflon screw cap was used to storing sample that was preserved for Hg analysis. These sample bottles were laboratory pre‐washed with nitric acid (10%, v/v, 65% Suprapure®, MERCK, Germany) and deionized water prior to sampling.
Sample filtration, using a 0.45 μm pore size filter, is required for the determination of dissolved constituents in water quality study. A filtration step removes two types of materials: (1) bacteria and phytoplankton (which may alter the concentration of measured content by uptake, breakdown of organic/polymeric fractions); (2) particulate materials (which may adsorb or release the analyte during storage). Filtration is, in particular, an essential pre‐treatment process for water samples collected in remote sites where immediate accessing to a laboratory is not feasible. In this study, all water samples subjected to a laboratory instrumental analysis of dissolved contents were filtered through a 0.45 μm disposable cellulose acetate syringe membrane filter (33 mm diameter, white rim, Whatman GmbH, Germany) immediately after collections. Sample bottles were all filled with the filtrate to the top, leaving no airspace, and capped immediately. Sampled bottles were then stored in double PE bags and kept at 4 °C until analysis.
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4.3 IN-SITU MEASUREMENTS
Labile quality parameters, such as pH, electrical conductivity (EC), water temperature and turbidity, have to be measured in the field.
A portable pH meter with automatic temperature compensation and accuracy of ± 0.02 pH units was used for in situ pH measurements. Together with the pH meter, a portable EC meter (accuracy: ± 1% of full scale) with temperature sensor (accuracy: ± 0.5 °C) was used for EC and water temperature measurements. An unfiltered sample collected in a 15 mL glass sample vessel was subjected to turbidity measurements using a portable turbidity meter (accuracy: ± 2%) on site.
4.4 LABORATORY ANALYSES
4.4.1 Major cations and trace elements Major elements and trace elements are present in the aquatic system in both dissolved and particulate forms. They can originate from both natural sources (e.g. from the weathering of rocks and erosion within the sediment) and anthropogenic (e.g. mining discharge, industrial and domestic waste disposals, and long‐range transported pollutants) inputs. Elevated levels of trace elements in environmental compartments are usually caused by human activities (Gaillardet, et al., 2003). Among a wide variety of pollutants effecting water quality, some trace elements (e.g. Ag, As, Cd, Cr, Hg, Mo, Ni, and Pb) receive particular attention due to their toxicity even at low concentrations. Some of these have also bioaccumulation‐ and biomagnifications‐ properties.
Among the analytical methods that have been used in determination of metal concentrations in water, the atomic spectrophotometric method combined with inductively coupled plasma (ICP) has become the most extensively used. This is because the ICP techniques are the most accurate, sensitive, and reliable methodologies for water analysis (Marcovecchio, et al., 2007, p. 287), and they allow simultaneous multiple elements determination. Typically, a water sample aliquot is aspirated into a
40
nebuliser, and a proportion of aerosol generated by the nebuliser is passed into an argon plasma torch that has a very high temperature (6 000‐8 000 K); the sample is then efficiently atomized within the plasma. The atoms are excited by the high temperature to an electronic level whereupon they emit light when they relax back to ground state; the emission at an element characteristic wavelength is detected. The intensity of emission recorded is proportional to the number of atoms and molecules undergoing the transition and provides quantitative information. Only a few molecular species are stable at such high temperatures as generated by the plasma and interference from molecular emission is hence minimized.
For the ICP determinations, samples were acidified using conc. nitric acid to < pH 2 prior to the analysis. Filtered water (water soluble fraction) samples for most of metal concentrations were determined by an ICP‐optical emission spectrometry (ICP‐OES, Papers I and IV, 2006 samples) and an ICP‐atomic emission spectrometry (ICP‐AES, Papers II‐IV). ICP‐AES operating conditions are present in Appendix II, while chosen wavelength in ICP‐AES for each element and corresponding limit of detection (LOD) are listed in Appendix III. The accuracy of the ICP‐AES method was revealed by recovery percentage of the quality control analysis, and precision of the method was evaluated by duplicate analysis of the standard reference materials (see details on validation of ICP‐AES in Paper II). Data presented in Paper I for Cu, Ag, Mo, Cr, Cd and Ni were determined by using a graphite furnace atomic absorption spectrometry (GFAAS) due to its high sensitivity and low detection limits available at the time of analysis.
4.4.2 Mercury Dissolved mercury (Hg) is in natural waters believed to be mainly present in its inorganic form (Hg2+) (WHO, 2004). Hg is of special concern due to its high toxicity even at very low concentration. However, duo to its high volatility and general low concentrations most analytical techniques do not have sufficient sensitivity to produce significant results for Hg concentrations in natural water. In this study, total dissolved Hg concentration in water samples
41
collected in 2006 (Paper I) and 2007 (Papers II and IV) were analyzed using flow injection‐atomic absorption spectrometry (FI‐AAS), with a LOD value of 0.001 mg Hg/L. While samples collected in 2008 (Papers III and IV) were subjected to a cold vapor‐ atomic fluorescence spectrometry (CV‐AFS) analysis (SFS, 2008), giving a limit of quantification (LOQ) of 2 ng Hg/L. For all the Hg content determination samples were acidified using conc. nitric acid to < pH 2 prior to the analysis.
4.4.3 Anions and NH4+ All inorganic ions contributing significantly to the anionic charge can be separated and determined by ion chromatography (IC). IC application in water analysis has been accepted as standard method for anion determination worldwide (e.g. EPA, 1993). The principal and instrumentation used for IC is analog of that for HPLC using an ion exchange resin as the stationary phase. The separation of ionic species takes place depending on their ion exchanging affiliation with the resin, when sample is eluted through the column with a mobile phase. A conductivity detector is commonly used for measuring the electrical conductivity of this eluting mobile phase. Details on IC instruments and operating conditions in this study, for both major anions and NH4+, are presented in Appendix IV.
4.4.4 Total dissolved sulfur Total dissolved sulfur (S) in the water sample was quantified together with metal analyses, using the ICP‐AES method as described above (in section 4.4.1).
4.4.5 TDP, TDN and silica Total dissolved phosphorus (TDP) is measured in 0.45 μm filtered samples using the phosphormolybdenum blue (PMB) method, following a strong‐acid digestion. This digestion process is intended to decompose organic P, polymeric and colloidal P into orthophosphate. When phosphate is mixed with molybdate ions in an acid solution, 1,2‐molybdophosphoric acid is formed, which is reduced to the PMB complex in a presence of a reducing agent (e.g.
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ascorbic acid). The intensity of this blue color is proportional to the amount of orthophosphate ions in the complex hence it can be determined spectrophotometrically.
In this study data for TDP were partially obtained from measurement based on a formation of antimony‐phosphomolybdate complex reduced by ascorbic acid after nitric‐perchloric acid (HNO3‐HClO4) digestion (Papers II and IV, 2007 samples). This method is adapted as Chinese state standard method for TDP analysis in natural water and wastewater (SEPA, 2002). Other part of data (Papers III and IV, 2008 samples) were obtained spectrophotometrically based on a formation of PMB complex reduced by ascorbic acid, followed after a persulphate (potassium peroxydisulphate, K2S2O8) autoclaving digestion process in the presence of sulphuric acid (SFS, 2004).
Natural river waters in the Tibetan Plateau have in general an oligotrophic characteristic. Monitoring the changes of TDP concentration is therefore a proxy for sewage inputs to the aquatic environment in the region, especially downstream from the rapidly expanded cities and industrial sites.
Total dissolved nitrogen (TDN) concentration in samples collected in 2007 (Paper II) were quantified by a non‐dispersive infrared detector, following oxidation of nitrogen to nitrogen oxides (SFS, 2003). In this method the nitrogen in the water sample is converted to nitrogen oxides by catalytic (cerium oxides) combustion in an oxygen atmosphere at 800 °C.
The concentration of total dissolved SiO2 in samples collected in 2007 (Paper II) was measured directly using an ICP‐OES, while atomic absorption spectrometry (AAS) was applied for the samples collected in 2008 (Papers III and IV).
4.5 STATISTIC METHODS AND DATA ANALYSIS
Mathematical and statistical computations and graphical presentations were made using Excel 2003 and SigmaPlot. Multivariate analysis was conducted using principal component analysis (PCA), available in Minitab.
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In the PCA, each object (sample) is positioned in a multi‐dimensional space described by the variables, i.e. quality parameters (QPs), the two coordinates (principal components, PCs) that represent the largest (PC1) and second (PC2) largest variances among the samples are computed simultaneously. In this way the interrelationship between the samples can be described in two dimensions without considerable loss of the total original variance. In the resulting PCs‐loading plots (PC2 vs PC1), the original variances, i.e. QPs, are displayed in the coordinate system and the correlation among these QPs are shown. In the plot, QPs with high (positive or negative) values along the PC have great importance for that PC accordantly, and QPs located closely together are positively correlated, and vice versa.
In this study, only samples with relatively complete measurements were included in the computation. For some important QPs, missing data, i.e. measured value below LOD was replaced with [(LOD)/2] value. QPs with more than half of the data below LOD value were omitted from the PCA analysis.
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5. Results and discussion
5.1 DATA COLLECTION
A total of 34 physiochemical quality parameters were measured in water samples in this study (described in Chapter 4 and Papers I‐IV). Spatial variation of these parameters in the Tibetan rivers was shown by data obtained from a total of 159 sampling sites, with a topographic relief from 4 800 m a.s.l. to 1 700 m a.s.l., along the four major Asian rivers draining in the Tibetan Plateau. Temporal variation was studied by comparing data obtained in the 2006 sampling campaign (mainly trace elements data) representing the water chemistry at low flow (sampled in spring before rain starts) and data from samples obtained at the same sampling sites in 2007 and 2008 (sampled just after the rainy season). The latter are given as average values representing chemical load in the rivers during high flow.
5.2 WATER CHEMISTRY OF THE TIBETAN RIVERS
Tibetan rivers have a fairly high buffering capacity. It is reflected by their average pH values, which range from 8.4 to 8.7. This is higher than that of the global average (between 6 and 8.2, Meybeck, 2003).
The distribution of major ions in the Tibetan rivers is somewhat different from that of other pristine rivers in the world (Table 1). Despite considerable variation in geology, lithology and climate among individual rivers and along these large river catchments, the distributions of ionic contents in the Tibetan rivers are relatively homogenous. The similarities are indicated by a low percentile ratio (Q99/Q1), ranging from 5 to 16. The exceptions are for Na+ and Cl‐, which is due to the influence of evaporites and drainage from saline lakes in the region.
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Table 1: Major ion distribution in the Tibetan rivers (the Yangtze River, the Mekong River, the Salween River, the Yarlung Tsangpo and their tributaries in the Tibetan Plateau, n = 124) compared to that of the World’s rivers.
Ca2+ Mg2+ Na+ K+ SO42- Cl- HCO3
- SiO2 ∑+
Major ion contents in Tibetan rivers a
Q99 2 751 1 575 3 325 147 1 977 3 743 3 027 168 7 547
Q1 520 149 39 9 189 39 271 32 744
Q99/Q1 5 11 86 16 10 96 11 5 10
Ionic proportions (%) of Tibetan rivers a
Q99 81 36 44 3 49 50 84 - -
Q1 34 11 3 0 9 2 20 - -
Upper
quartile
69 23 15 1 35 11 70 - -
Major ion contents in World's rivers b
Q99 9 300 5 900 14 500 505 14 500 17 000 5 950 680 32 000
Q1 32 10 18 4 5 4 47 3 128
Q99/Q1 291 590 806 129 2 900 4 595 127 206 250
Ionic proportions (%) of World's rivers b
Q99 84 48 72 19.5 67 69 96 - -
Q1 11 0.1 1 0.1 0.1 0.1 9 - -
a The present study; b Meybeck, 2003. Note: Ion contents are in μeq/L, except SiO2 is in μmol/L; ∑+ is the sum of cationic contents; Ionic proportion (%): proportion of ions in the sum of total cations or anions; Q1 and Q99: the lowest and highest percentiles of distributions. Mean value (in mg/L) of the major solutes in the rivers in the
Tibetan Plateau is given in Appendix V. These are compared with similar data from other parts of the world. The illustration presented in Figure 2 shows that the major solutes in the Tibetan rivers (given as mean values of four river catchments) are on average two times higher than mean values of waters from the rest of the world (Wetzel, 1975). The exception here is for SiO2. In general, the concentration of SiO2 in Tibetan rivers is only 1/3 of that of other rivers in the world and account for less than 5% of TDS. This is significantly lower than that of the world’s rivers. According to Meybeck and Carbonnel (1975 and references therein)
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the SiO2 contributes about 10% of the TDS. Elevated concentrations of Na+ and Cl‐, along with SO42‐, in these rivers are largely due to strong evaporation caused by a negative water balance, dissolution of evaporites and some drainage from saline lakes. Contribution of atmospheric sea salt to the Tibetan waters can be disregarded. An important source of SO42‐ in the Tibetan rivers is the oxidation of sulfides present in the catchments. This has also been demonstrated in other studies on the Plateau (e.g. Galy & France‐Lanord, 1999; Hren, et al., 2007). In general the ionic contents of Tibetan rivers are comparable with waters in Europe with respect to the other parameters which are not mentioned above (e.g. Ca2+, Mg2+, and HCO3‐, see Appendix V).
0
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mg/
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C in
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Water quality of Tibetan rivers compared to the "rest of the world"
Tibetan PlateauWorld
Mg2+Ca2+ Na+ K+ NO3- HCO3
- SiO2SO42- Cl- EC
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Water quality of Tibetan rivers compared to the "rest of the world"
Tibetan PlateauWorld
Mg2+Ca2+ Na+ K+ NO3- HCO3
- SiO2SO42- Cl- EC
Figure 2: Major ion concentrations in the Tibetan rivers, given as mean values, and compared to the world’s average (Wetzel, 1975). Data source: Appendix V.
Mean values of TDS for the four rivers studied here are illustrated in Figure 3, and compared with similar means from other parts of the world. In general, easily weatherable carbonates are the dominant source of major ions in these rivers (Figure 2), even when only small amounts are present in the catchments (Hren, et al., 2007; Singh, S.K., et al., 2005). In addition, dissolution of evaporites, some drainage from brackish/saline lakes and
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geothermal waters are important contributors to the high TDS in the Tibetan rivers (Wu, et al., 2008b). Silicate weathering plays also a significant role in contributing major solutes in these rivers (Tipper, et al., 2006b; Wu, et al., 2008a, 2008b). TDS in these rivers decrease downstream in the river courses. This is coincident with the annual aridity (annual aridity = annual evaporation loss/ annual precipitation), which declines about 10 times from these rivers’ headwater regions in the west and north parts of the Plateau to the east and southeast (Zheng, 1997, p. 55).
0
50
100
150
200
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TDS
(mg/
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SalweenRiver
Mekong River
YangtzeRiver
AfricaAsiaEuropeYarlungTsangpo
NorthAmerica
SouthAmerica
World0
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(mg/
L)
SalweenRiver
Mekong River
YangtzeRiver
AfricaAsiaEuropeYarlungTsangpo
NorthAmerica
SouthAmerica
World
Figure 3: TDS in the Tibetan rivers, compared to TDS of other rivers around the world (Wetzel, 1975). Data source: Appendix V.
Like the other rivers studied around the world (Meybeck, 2003; Wetzel, 1975), Ca2+ and HCO3‐ are the dominant ions also in the Tibetan rivers (Papers I‐III). This is illustrated in Figure 4 and indicated by the upper quartile in the Table 1. Sulfate also plays a significant role in the Tibetan rivers, while Cl‐ is about as important as HCO3‐ in the Yangtze River samples.
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Mekong River Salween RiverYangtze River Yarlung Tsangpo
µeq/
L
Ca2+
Mg2+
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NO3-
Left bar Right bar
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Mekong River Salween RiverYangtze River Yarlung Tsangpo
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L
Ca2+
Mg2+
Na+
K+
Ca2+Ca2+
Mg2+Mg2+
Na+Na+
K+K+
HCO3-
SO42-
Cl-
NO3-
HCO3-HCO3-
SO42-SO42-
Cl-Cl-
NO3-NO3-
Left bar Right bar
Figure 4: Chemical compositions of Tibetan rivers, given as mean values of all samples in the catchments.
Natural levels of dissolved trace elements in river water are
thoroughly studied in the North America and Europe (e.g. Gaillardet, et al., 2003). In contrast there is very little information on the background levels of these elements in Asian rivers. This is rationalized to be due to a low abundance of the trace elements in the rivers as a result of their high pH value (Gaillardet, et al., 2003). Average values, based on all data collected in this study (Papers I‐III), are presented in the Table 2 and are compared with the world average (Gaillardet et al., 2003). The data suggest that the levels of trace elements in the rivers on the Plateau are rather high, although the waters are alkaline (Table 2). A comparison of the data in the Table 2 should be interpreted carefully as the dissolved contents are strongly dependant on the filtration procedure. The data for the world average, reported by Gaillardet et al. (2003), was obtained after filtration using either 0.2 μm or 0.45 μm filters. The 0.45 μm pore size was used throughout the present study. It should be pointed out that the elevated levels of, in particular of Fe, Al, and Pb, were mainly found in samples collected before the rain seasons (Paper I). In‐situ turbidity measurements showed that the Tibetan rivers, especially the main river streams during the high flow (just after heavy rain season) were rich in particulate matters (turbidity
50
> 1 000 NTU). As the rivers in the Plateau are low in dissolved organic matter (DOM), these elements will not be present in significant amounts as organic complexes, which may be rather common elsewhere in the world. One may speculate, however, that there might be some inorganic complexes of Fe, Al or Pb present in these turbid waters that keep these heavy metals in a non filterable state. Temporal variation of these elements is discussed in next section.
Table 2: Trace elements levels in the Tibetan rivers (i.e. the Yangtze River, the Mekong River, the Salween River, the Yarlung Tsangpo and their tributaries in the Tibetan Plateau), compared to that of the world average. All the elements are in unit μg/L
Tibetan rivers a World b
Range Average Upper
quartile Range Average
pH 7.7 - 9.2 8.5 8.6 4.6 - 8.3 -
Ag < 0.001 - 0.15 0.02 0.02 - -
Al 1.4 - 2320 95.5 41.0 0.50 - 1080 32
As < 2.0 - 262 18.2 15.6 0.11 - 2.71 0.62
Cd < 0.02 - - 0.001 - 0.42 0.08
Co < 0.02 - 31 1.9 1.1 0.01 - 0.43 0.148
Cr < 0.05 - 2.7 0.7 0.8 0.24 - 11.46 0.7
Cu < 0.01 - 14.6 3.1 3.7 0.23 - 3.53 1.48
Fe < 3.4 - 6680 164.7 30.5 1.40 - 739 66
Li 0.01 - 298 37.4 54.2 0.16 - 10 1.84
Mn 0.2 - 242 12.7 10.8 0.41 - 114 34
Mo < 0.6 - 20.1 3.4 3.1 0.04 - 2.31 0.42
Ni < 0.02 - 104 11.1 4.7 0.12 - 10.39 0.801
Pb < 0.1 - 781 56.5 15.2 0.01 - 4.10 0.079
Ti < 0.2 - 3.1 0.7 0.7 0.001 - 5.81 0.489
Zn 0.03 - 29.2 4.4 5.0 0.04 - 27 0.6
a The present study (data used from Papers I‐III); b Gaillardet, et al., 2003.
Nutrients, measured as TDN and TDP in the Tibetan rivers, were at the level of 0.3 ± 0.2 (mg N/L) and 0.04 ± 0.03 (mg P/L) (Paper II). The level of dissolved F‐, PO43‐ and NH4+ were below LOD values (Papers II and III).
It should also be noted that the relatively high average level of As was mainly due to the very high concentrations in the upper
51
part of the Yarlung Tsangpo (avg. 95 μg As/L, Paper III). The concentration level ranged from < 2.0 to 73 μg As/L (avg. 9.5 μg As/L) in the most of the river reaches. On the other hand, from a drinking‐water quality point of view, it is important to emphasize that the concentrations of Ag, Cd, Co, Cr, and Hg in the Tibetan rivers are negligible in both seasons (Papers I‐III).
5.3 RIVER WATER QUALITY
Temporal variation of some quality parameters in the Tibetan rivers is presented in the Table 3. The concentrations of Al and Fe varied considerably in all the rivers, being on average 16 and 24 times higher in the low flow season (Paper I) compared with the high flow season (Papers II and III). The values of pH and EC remained relatively constant. The level of Zn, however, was lower during spring time.
5.3.1 Yangtze River The content of TDS in the Yangtze River was clearly different from the three other rivers (Figure 3). Na+ and Cl‐, from the influence of evaporites and drainage from saline lakes in the region, are the major cause for the high TDS (Figure 4). This is especially the case at the upper reaches of the river. In addition carbonate weathering contributes significant to the contents of Ca2+ and HCO3‐. The tributaries of the river had lower contents of salts, causing the major water quality parameters in the main stream to show a clear dilution 800 km downstream with elevation decline of about 1 400 m (Paper II). It should be noted that a relatively high concentration of Li, found in the river catchments during the high flow season, was not observed in the low flow season. Ni level in the river showed the opposite trend. Concentrations of Pb were low in both seasons (Table 3).
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Table 3: Seasonal variations of some quality parameters of the Tibetan Rivers (i.e. the Yangtze River, the Mekong River, the Salween River, the Yarlung Tsangpo and their tributaries in the Tibetan Plateau). Comparison is made in the same part of the river catchments that was sampled in both seasons
Yangtze River Mekong River Salween River Yarlung Tsangpo
LF HF LF HF LF HF LF HF
pH 8.5-9.2 8.4-8.5 8.5-8.7 8.5-8.5 8.6-8.8 8.3-8.5 8.4-9.0 7.7-8.5
EC 19-120 17-71 29-67 39-43 20-39 15-28 9-34 8-24
Mg 11-79 3-19 26-58 14-16 18-51 3-13 5-35 2-8
Al 80-600 9-37 160-220 9-16 130-400 5-31 80-2320 13-80
Co 0.04-1.2 <0.7 <0.02-1.6 <0.7 0.2-4.8 <0.7 <0.02-31 <0.7
Cr 0.4-1.1 <0.8 0.3-1.4 <0.8 0.3-0.9 <0.8 <0.05-2.7 <0.8
Cu <0.01-3.9 <1.8-4.3 0.5-2.2 <1.8-7.3 <0.01-1.2 <1.8-1.8 <0.01-13 <1.8-6.2
Fe <60-890 <3.4-38 <60-130 <3.4-12 110-410 11-29 <60-6680 <3.4-61
Li 0.3-41 2.2-70 17-39 16-21 3.7-32 3.7-13 3.2-93 2.5-42
Mn 14-64 0.6-15 13-61 1.4-5.8 11-34 3.5-6.2 0.5-242 0.5-154
Mo 5.1-11 <0.6-1.7 11-13 0.7-1.2 4.5-20 <0.6-2.0 5.2-17 <0.6-2.0
Ni 0.7-64 <0.9 0.8-3.6 <0.9 0.5-18 <0.9 <0.02-104 <0.9
Pb <0.1-2.9 <4.2 2.5-15 <4.2 <0.1-781 <4.2 <0.1-130 <4.2
Zn 0.7-2.8 2.0-5.0 0.8-3.6 3.1-5.4 0.5-18 2.7-7.8 <0.02-29 2.0-21
LF: low flow (April‐May); HF: high flow (late Aug.‐early Oct.). EC in unit mS/m, concentrations of Mg in mg/L and others are in μg/L.
5.3.2 Mekong River The content of TDS in the Mekong River is high and comparable to that of the Yangtze River (Figure 3). Notable is the large contribution of SO42‐ to the anionic charge (Figure 4). This is mainly from gypsum evaporites and oxidation of sulfide minerals. There were only 15% to about 20% decrease in levels of EC, SO42‐, Ca2+ and TDS in the river main stream along a 500 km distance, with an elevation decline of more than 1 500 m (Paper II). The main reason for this was that the quality of the two main tributaries, Dzachu and Ngomchu, was only slightly different from that of the main stream. Influence of sewage effluents from the Chamdo town on the level of dissolved nitrogen was observed (Paper II). Concentrations of Pb were fairly low also at low flow (Table 3).
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5.3.3 Salween River The Salween River, with the lowest TDS (Figure 3), seemed to be the most dilute water among all studied rivers despite the existence of some limestone in the catchment. However, it should be kept in mind that in this work only a small part of the main Salween River was included. It should be noted that two tributaries Yuchu and Lengchu had even lower levels of TDS, with less Ca2+, Mg2+ and HCO3‐, relative to the main steam. Furthermore, the concentration level of SO42‐ is about half of what was found in the main stream (Paper II). Elevated concentration of Pb was found, both in the main river and its tributary Lengchu, during the low flow. This is partly explained by vehicle emissions from the highway (G318) and possibility due to atmospheric deposition (Paper I).
5.3.4 Yarlung Tsangpo A relatively intensive sampling (n = 85) was performed along the Yarlung Tsangpo river, including all five major tributaries: Raga Tsangpo, Nyangchu (in the middle reaches of the river catchments), Lhasa River, Nyangchu (in the lower reaches of the river in the southeast Plateau) and Parlung Tsangpo.
The chemical composition of the Yarlung Tsangpo and its tributaries is, with regards TDS, rather similar to the quality of the European rivers (Figure 3). The lack of easily weatherable carbonate rocks in the majority part of Yarlung Tsangpo catchments (Hren, et al., 2007) can be the cause for the lower TDS. This is particular the case when Yarlung Tsangpo is compared to the Yangtze River and the Mekong River. The river and its tributaries are also of the calcium carbonate type. SO42‐ is the second most abundant anion in the river (Figure 4). Na+ and Cl‐ are significant only at the river headwater areas. The concentrations of most major ions in the headwaters section of the main stream increased slightly as more salt‐rich waters merged into the main stream, and reached the highest values before the Raga Tsangpo confluence (Paper III). Below this tributary there is a general tendency of a decreasing ion‐content (Papers II and III).
It should be emphasized that the headwaters had also elevated concentrations of SiO2, Li, Mo, and especially As (avg. 95 μg/L),
54
indicating a silicate weathering source of these solutes. The high levels of As in the headwaters result in elevated As concentration 1 200 km downstream, with a linear decrease in the concentration due to overall dilution along the river course (Paper III). Nyangchu (in the middle reaches of the river catchments) had higher TDS than other tributaries to the Yarlung Tsangpo (Paper III). Lhasa River, which is the largest contributor to Yarlung Tsangpo, exhibits some anthropogenic influence on the level of dissolved nitrogen and heavy metals from domestic, agricultural and industrial (mining) activity (Papers II and III). This tributary, the Lhasa River, and thereby also Yarlung Tsangpo, is under high risk of heavy metal pollutions, due to poor managements and the rapidly increased mining activities in the river catchments (Paper IV).
5.4 MAJOR CONTROLLING FACTORS OF THE TIBETAN RIVER
CHEMISTRY
Mechanisms governing the water chemistry of the Tibetan rivers were assessed by identifying inter‐correlation of the quality parameters, using the PCA. The results show that the composition of dissolved chemical constituents of the Tibetan rivers is strongly influenced by carbonate weathering (Papers II and III). The results also illustrate that the level of some other ions, such as Na+, K+, Li, Cl‐ and SO42‐, are strongly controlled by up‐concentration, due to evaporation in the headwater areas, and dilution downstream. Dissolution of evaporites and some drainage from saline lakes and geothermal springs play also a significant role in controlling the level of these ions in the rivers (Papers II and III). It is believed that 90% of dissolved Li loads in the Himalayan rivers are derived from silicate weathering (Kısakűrek, et al., 2005). However, input from saline lakes, geothermal springs and dissolution of evaporites are likely to be the main source of the Li found, in particular, the Yangtze River in the Tibetan Plateau. High concentrations of Li were not observed in the spring period due to the low flow and consequently less input of these ions from the lakes and geothermal waters. The data obtained in this study shows that
55
primary source of SO42‐ in the Yangtze River catchments and a major tributary of the Yarlung Tsangpo, the Nyangchu in the middle reaches of the main river, is evaporites (Papers II and III). However, SO42‐ in the Yarlung Tsangpo is mainly derived from sulfide oxidation (Paper II).
The levels of trace elements in surface water are strongly governed by the pH through its influence on the solubility (Gaillardet, et al., 2003; Dupré, et al., 1996). This was not clearly shown for the Tibetan rivers (Table 2; Papers II and III). The reason for this might be complex and partly due to input from drainage of metal‐ions enriched saline lakes (Tian, et al., 2002; Yu, 1992; Zheng, 1997) (Papers II and III). Furthermore, elevated heavy metal concentrations found in the rivers during low flow season might be due to the melting snow and ice, in which long‐range transported pollutants have accumulated and released (Paper I). It is indeed important to emphasize that only the dissolved phase has been considered in the present study. The elements that are commonly associated with particles, e.g. Al, Fe, Cu, and Pb, were filtered off through the filtration procedure and, therefore, not detected by the applied methods.
In summary, the major controlling factors for the spatial variation of water quality of the Tibetan rivers are the differences in lithology and changes in climatic environment along the river course. This is in agreement with the relatively homogenous water quality as indicated by the low Q99/Q1 ratio. A short term quality monitoring, such as the present study, is, therefore, indeed useful for an overall understanding of the chemical properties of these rivers in the Tibetan Plateau. An impact of discharge of untreated municipal wastewater and mining effluents is detected, in particular, in the Yarlung Tsangpo catchments (Papers I‐IV).
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5.5 DRINKING WATER QUALITY – A CASE STUDY IN LHASA
CITY
Lhasa city (3 650 m a.s.l.), with 180 000 inhabitants, is located in the north bank of the Lhasa River. Centralized water supply from deep groundwater well (30‐50 m) was established in 1979. To date, the system consists of four supplies that are located in four sections of the city. In total, it has a serving capacity of 260 000 m3/d and covers water supply for 87% of the city usage. So far no major water‐related health effects have been reported in the city, nevertheless, the water is recommended to be boiled prior to consumption.
A total of 34 tap water samples were collected from ten households (A‐J), representing the water supply in the west section (WWS), centre section (CWS‐A) and north section (NWS) of the city. Three samples through a day (i.e. morning first portion of the tap water sample, midday sample, and evening sample) were collected from each household. All water samples were subjected to same analysis as described above. Chlorine residuals were not included in the analytical program as the water treatment is limited to filtration. The results are present in the Appendix VI. The data shows that in general the drinking water quality of the city is acceptable relative to the chemical quality standards set by both WHO (2004) and MOH & SAC (2006). Common drinking water problems with F‐ and As found in neighboring countries (MoEF, 2009 among others) were not observed in Lhasa city drinking‐water. Like the surface water in the region, Ca2+ and HCO3‐ are also the dominant ions in the drinking‐water, while the concentration levels of most heavy metals are below detection limits (Appendix VII). However, the levels of Fe and Zn were in some samples a cause for concern. The high concentration levels of Fe and Zn, especially in the morning samples, are due to corrosion from the pipelines. The Langelier saturation index (LSI) and Ryznar stability index (RSI) (Tchobanoglous & Schroeder, 1987) (Appendix VIII) values confirm corrosion conditions and potential scale formation of the drinking water in the city.
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5.6 MINING IMPACT ON THE SURFACE WATER QUALITY – A
CASE STUDY IN GYAMA VALLEY
Gyama valley, situated south of the Lhasa River, about 70 km upstream from Lhasa city, is one of the most intensively mining exploited areas in T.A.R. The work presented here, is based on the chemical evaluation of the stream, Gyamaxung‐chu, draining the valley. It is the first study of surface water quality and chemical impact assessment of mining activities in the entire region, despite the fact that industrial scale mining operations have been ongoing for nearly 20 years.
Chemical characterization of dissolved constituents in the stream water of Gyamaxung‐chu and wastewater treatment facilities in the Gyama valley identified a severe heavy metal contamination locally. The contents of heavy metals, such as Pb, Cu, Cd and Zn, represent a high risk for the environment. In spite of low pH and high dissolved heavy metal concentrations in the upper reaches of the stream, the reduced levels of pollution pose probably no risk only 10 km further downstream. This is mainly due to the natural high buffering capacity of ground water seepage, causing the pH to increase and the heavy metals to precipitate or adsorb to the streambed sediments. The many mining activities and processing deposits in the valley, containing large amounts of heavy metals, such as Pb, Cu, Zn and Mn, are of considerable environmental concern. These deposits are prone to leak its contaminants through seepage water and erosion of particulates, and pose therefore a future risk for the local environment and a potential threat to the downstream water quality. Changing climate, causing increased frequency and intensity of runoff, will likely cause enhanced transport of contaminated particles from the tailings and streambed in the future. Furthermore, the changes that have occurred in recent years demonstrate clearly that deposited heavy metals in the river sediments may readily be re‐mobilized if the water becomes more acidified due to enhanced mining activities. The characteristics of the tailings containing gangue material and low grade ore as well as finely milled material from the processed ore have not been
58
properly studied. Any further operation, prior to a proper assessment, should therefore be carefully considered before taking action.
59
6. Conclusions and further research
This study provides an overview of the water quality of four of the world’s large rivers draining the Tibetan Plateau.
The results show that the spatial distributions of major solutes in these Tibetan rivers are relatively homogenous and are mainly controlled by the differences in lithology and differences in climatic conditions along the river courses. The amounts of dissolved solutes in the Tibetan rivers are on average twice that of rivers elsewhere in the world. The generally high content of TDS in the Tibetan waters is, as commonly found, mainly due to high levels of Ca2+ and HCO3‐, derived from carbonates weathering. Contributing additionally to the total ionic loading are elevated concentrations of Na+ and Cl‐, largely due to the influence of evaporites and some drainage from saline lakes and geothermal springs on the Plateau. Sulfate, mainly from oxidation of sulfides present in the catchments, is also contributing significantly to the high levels of TDS.
This study reveals that in spite of the alkaline nature of these waters, the average levels of dissolved trace elements in the Tibetan rivers are rather high relative to that of rivers from other parts of world. Notable is that this is referring to the dissolved fraction only. Since particulate transport of contaminants, and especially heavy metals, is known to be important in such turbid and alkaline waters, the filtration procedure, employed in this study, may play a significant role in influencing the actual values. A considerable temporal variation between low‐ and high flow seasons was found for Mg and 14 trace elements. This is in particular the case for Al and Fe, being on average about 20 times higher during the low flow season compared to the high flow period. The Tibetan rivers, especially the main streams, are highly turbid (turbidity > 1 000 NTU) during the high flow period. It
60
should be pointed out that the particulate fraction of the elements, such as Al and Fe, commonly associated with particulate matter, were excluded in this study due to the field filtration procedures.
The results show that the headwaters of these Asian major rivers in the Tibetan Plateau can in general be considered as pristine, with negligible levels of Ag, Cd, Co, Cr, and Hg in regards to established standard for drinking‐water quality. Nevertheless, the inputs from saline lakes and geothermal springs are important sources for especially Pb and As. Influence of municipal wastes, identified in some locations by elevated concentration of dissolved nitrogen, is still below any ecological concern. However, this study identifies severe heavy metal pollution in one particular major tributary of the Yarlung Tsangpo. This is partly due to, and influenced by, the poorly regulated mining operations within the area.
It is utmost important to maintain the quality of the Tibetan rivers as it is vital for the lives of more than one third of world’s populations. Our present work has contributed to an overall view and understanding of the chemical state of the environment in the headwaters of four major Asian rivers. The most important needs for future studies are addressed below: 1. The content of particulate matter is considerable in all the
studied rivers. Future research on contaminant levels and fluxes must put efforts on the role of their particulate fraction suspended in the water as well as contaminated river sediments. By this manner, total chemical fluxes in these rivers can be assessed and factors controlling the concentration levels of trace elements in difference phases may be identified.
2. As mining industry starts playing a prominent role in the region’s economic development, studies are required that provide better understanding of the environmental impact of the mining effluent, especially their tailings of gangue and ore processing material. Environmental regulations are poorly implemented on the Plateau and the present mining activities are also inadequately managed. Large amounts of heavy metals in their freely exposed tailings are prone to leak through seepage water and erosion of particulates, and constitute a
61
potential threat to both groundwater and downstream water quality. A water quality monitoring program targeting the effect of the rapidly increased mining activities over the whole Plateau should also be implemented in order to ensure the public safe water in the future.
3. Future changes in water quality on the Tibetan Plateau as consequences of enhanced weathering and erosion due to climate change need also be addressed. In addition, evaluation of the contribution of brackish/saline lakes and geothermal springs to the chemical flux of the Tibetan rivers should also be considered. These studies, if carried out, would enhance the present
knowledge and understanding of water chemical properties in the region. Essential information on the quality state and possible future change can also be provided to the public.
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63
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8. Appendices
Appendix I: Guideline values in water quality; except pH, all units are in mg/L WHOa Remark GB5749b Remark GB3838c Remark
Grade I Grade
II
pH No Optimum:
6.5-9.5
6.5-8.5 6-9 6-9
Ammonia No 0.5 Determined
as N
0.15 0.5 Determined
as N
Cl- No 250 - 250
F- 1.5 1.0 1.0 1.0
NO3- 50 For short time
exposure
10 Determined
as N
- 10 Determined
as N
SO42- No 250 - 250
Na No 200 - -
TDS No 1 000 - -
Ag No 0.05 - -
Al 0.2 Practicable level 0.2 - -
As 0.01(P) 0.01 0.05 0.05
Cd 0.003 0.005 0.001 0.005
Co - - - 1.0
Cr 0.05(P) For total
chromium
0.05 For Cr(+6) 0.01 0.05 For Cr(+6)
Cu 2 1.0 0.01 1.0
Fe No 0.3 - 0.3
Hg 0.001 For total
mercury
0.001 0.00005 0.00005
Mn 0.4 (C) 0.1 - 0.1
Mo 0.07 0.07 - 0.07
Ni 0.02(P) 0.02 - 0.02
Pb 0.01 0.01 0.01 0.01
Ti - - - 0.1
Zn No 1.0 0.05 1.0
To be continued
70
Appendix I continued
Total P - - 0.02 0.1
Total N - - 0.2 0.5
a WHO, 2004; b MOH & SAC, 2006; c SEPA & AQSIQ, 2002; No = no health based guideline value is provided; P = provisional guideline value, as there is evidence of a hazard, but the available information on health effects is limited; C = concentrations of the substance at or below the health based guideline value may affect the appearance, taste or odor of the water, leading to consumer complaints; Hyphen indicates there is no information provided.
Appendix II: ICP‐AES operating conditions
Instrument iCAP 6300Duo, Thermo Electron Corporation
RF power 1150 W
Plasma gas 12 L/min, argon
Nebuliser type Concentric glass nebuliser
Nebuliser gas pressure 200 kPa
Auxiliary gas flow 0.5 L/min
Nebuliser pump tubing type Tygon® Orange/White
Nebuliser pump flush rate 50 rpm
Nebuliser pump analysis rate 50 rpm
Sample flush time 30 s
Rinse time 30 s
Replicates 2
Calibration method External
Detector High performance CID86 chip
Data treatment iTEVA (software)
71
Appendix III: ICP‐AES: wavelength used for each element and corresponding limit of detection (LOD)
Element Wavelength
(nm)
LOD
(µg/L) Element
Wavelength
(nm)
LOD
(µg/L)
Al 1670 0.5 Mg 2802 0.3
As 1890 2.0 Mn 2576 0.1
Ca 3158 30.7 Mo 2020 0.6
Cd 2288 0.4 Na 5889 77.1
Co 2286 0.7 Ni 2316 0.9
Cr 2677 0.8 Pb 2203 4.2
Cu 3247 1.8 S 1820 3.4
Fe 2599 3.5 Ti 3349 0.2
K 7664 40.0 Zn 2138 1.5
Li 6707 1.5
Appendix IV: IC operating conditions
Instrument Metrohm 790 Personal IC
Measured ion NH4+ Cl-, NO3
-, SO42-
Column type 6.1010.000 METROSEP
Cation 1-2
6.1005.320 Anion column
Metrosep A Supp 3
Column size 4.0 x 125 mm 4.6 x 250 mm
Eluent 4 mM tartaric acid / 1mM
dipicolinic acid
1.7 mM NaHCO3 / 1.8 mM
Na2CO3
Eluent flow 1.00 mL/min 0.70 mL/min
Detector Conductivity detector
Instrument Metrohm 761 Compact IC
Measured ion Cl-, F-, HCO3-, NO3
-, PO43-, SO4
2-
Column Type AllsepTM Anion A-51207
Column size 4.6 x 100 mm
Eluent 4 mM p-hydroxybentzoic acid (pH 7.50, adjusted with LiOH)
Eluent flow 1.0 mL/min
Detector Conductivity detector
72
Appendix V*: Mean values (all samples in the catchments) of ionic concentrations (in mg/L) of the Tibetan rivers (the Yangtze River, Mekong River, Salween River, Yarlung Tsangpo and their tributaries in the Tibetan Plateau) compared to river and lake waters around the world. Here, TDS = ∑ (Ca2+ + Na+ + K+ + Mg2+ + Cl‐ + NO3‐ + SO42‐ + HCO3‐ + SiO2 in mg/L). EC is in mS/m
Rivers Ca2+ Mg2+ Na+ K+ SO42- Cl- NO3
- HCO3- SiO2 TDS EC
Yangtze River 40 12 38 2 53 64 0 108 5 324 44
Mekong River 49 14 12 1 69 14 0 138 4 302 37
Salween River 24 7 3 1 31 5 0 66 4 141 18
Yarlung Tsangpo 29 5 7 1 32 6 1 95 6 183 22
Tibetan Plateau 33 7 13 1 40 18 1 100 5 220 28
Europe 31 6 5 2 24 7 4 95 8 182 31
Asia 18 6 6 4 8 9 1 79 12 142 24
Africa 13 4 11 - 14 12 1 43 23 121 21
North America 21 5 9 1 20 8 1 68 9 143 25
South America 7 2 4 2 5 5 1 31 12 69 12
World 15 4 6 2 11 8 1 58 13 120 20
* Table modified after Table 2 in Paper II.
73
Appendix VI: Chemical characteristics of tap water in Lhasa City. Numbers indicate samples collected at different time of day, i.e., 1: morning first portion of the tap water; 2: midday sample; 3: evening sample. TDS = ∑ (Ca2+ + Mg2+ + Na+ + K+ + HCO3‐ + Cl‐ + NO3‐ + SO42‐ + SiO2)
Temp. pH EC Turb. Ca2+ Mg2+ Na+ K+ HCO3- Cl- NO3
- SO42- SiO2 TDS Al As Fe Mn Zn Li
0C mS/m NTU mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/Lµg/L µg/L µg/Lµg/L µg/L µg/L
A-1 17.6 7.65 24.6 1.47 33.2 4.8 8.3 2.06 134 7.6 5.9 21.5 10.1 227 1.8 <2.0 543 10.6 <1.5 50
A-2 18 7.57 24.6 0.18 33.5 5.0 8.0 1.42 137 7.3 20.3 20.2 11.2 244 <0.5 4.8 14.2 0.7 <1.5 47
A-3 17.1 7.54 25.1 0.09 33.8 5.0 8.0 1.46 136 20.6 17.5 21.1 12.1 255 <0.5 4.4 13.2 0.8 <1.5 45
B-1 16.2 7.7 37.4 1.1 58.9 4.1 9.0 1.07 146 14.0 29.0 23.1 9.9 295 <0.5 4.3 26 7 3 10
B-2 16.3 7.82 39.2 0.12 65.8 3.4 8.6 0.91 186 13.9 31.7 22.0 11.0 344 <0.5 3.7 25.6 3.5 2.2 2
B-3 16.6 7.59 29.7 0.18 41.4 5.5 10.5 1.55 109 9.2 26.6 24.2 11.6 239 1.2 <2.0 26.1 3.4 2.9 45
C-1 17 7.72 25.4 0.84 33.8 5.1 10.2 2.17 141 8.2 6.5 25.2 10.6 243 2.3 4.8 112 5.4 25.4 49
C-2 17.2 7.58 28.3 0.21 39.1 5.8 11.8 2.80 173 8.3 11.6 20.9 12.8 286 1.5 3.3 <3.5 7.6 8.2 51
C-3 17 7.47 30.2 0.38 39.9 5.9 12.0 3.01 170 9.1 13.3 21.3 12.0 286 2.4 5.3 12.3 7.3 8.9 50
D-1 - 7.76 21.4 0.54 27.7 4.3 7.8 1.32 97 7.9 2.8 21.0 7.7 177 <0.5 4.5 197 9 50 46
D-2 17.6 7.73 20.1 0.28 26.1 4.2 7.3 1.23 112 6.6 2.5 19.8 6.5 187 2.6 <2.0 11.3 6.7 30 46
D-3 17.6 7.8 20.5 0.27 27.2 4.2 7.4 1.26 116 6.2 2.4 19.7 7.8 192 2 2.4 17 3.8 30 46
E-1 18.6 7.5 31.7 1.11 40.7 5.9 12.5 3.25 171 25.3 15.1 26.4 12.3 312 <0.5 3.8 72 3.8 4 50
E-2 18.1 7.47 31.6 0.59 42.7 6.1 13.0 3.43 182 9.6 15.2 24.1 12.4 309 0.9 4.5 12.1 1.8 1.7 52
E-3 18.1 7.48 31.2 0.47 42.1 6.1 12.7 3.26 175 9.9 16.4 23.1 13.0 302 1 5.8 5.5 1.9 1.8 50
F-1 17.9 7.64 23.1 0.44 32.1 4.5 6.4 1.17 119 4.2 9.5 16.7 9.8 203 <0.5 <2.0 13 1.3 45 43
F-2 19.2 7.72 20.3 0.2 31.7 4.4 6.0 1.16 128 3.1 6.2 14.4 8.7 204 8.6 6.8 <3.5 <0.1 12.2 44
F-3 17.9 7.78 21.4 0.2 31.2 4.3 6.0 1.12 127 3.2 7.9 13.0 11.1 205 1.5 6.5 <3.5 0.2 12.1 43
G-1 18 7.46 33 4.46 43.4 6.1 13.1 2.13 159 11.6 27.8 24.5 12.5 300 6.2 2.8 70 5.2 386 54
G-2 19.4 7.45 32.6 0.28 42.4 6.0 12.9 2.08 150 12.4 31.1 22.8 10.9 290 1.8 5.7 9.4 3.5 267 53
G-3 20.6 7.4 32.5 0.2 42.4 6.0 12.4 2.07 138 11.3 27.2 24.7 10.3 275 2.2 <2.0 5.1 3.5 285 50
To be continued
74
Appendix VI continued
H-1 17.4 7.75 23.5 1.57 33.7 4.4 5.5 1.18 135 3.8 10.3 19.8 11.5 226 2.1 2.4 12 2.6 96 44
H-2 17.7 7.75 22.7 0.28 34.0 4.4 5.6 1.16 135 3.5 12.1 24.5 11.6 232 <0.5 4 <3.5 <0.1 6 42
H-3 18.2 7.74 22.7 0.04 34.9 4.5 5.7 1.16 137 3.3 10.6 22.1 12.1 231 1.4 3.2 3.2 0.2 9.2 44
I-1 15.9 7.9 21.8 0.6 28.1 4.4 7.6 1.39 117 8.2 3.4 22.6 6.9 200 6.6 3.6 <3.5 1.5 122 46
I-2 20 7.89 21.1 0.11 29.4 4.4 7.3 1.41 113 6.0 <1.0 22.9 7.9 192 7.3 2.3 9.5 0.9 11.2 48
I-3 19.4 7.89 20.6 0.37 27.6 4.3 6.6 1.33 120 5.6 3.6 20.7 7.1 197 6 5.1 13.3 0.9 40 46
J-1 14.7 7.53 30.4 0.21 39.2 5.7 11.0 2.08 146 9.6 20.3 21.5 10.2 265 2.7 4.3 114 5.1 6.3 50
J-2 16.5 7.6 28.1 0.11 39.4 5.5 10.7 2.00 133 8.7 18.9 20.6 10.5 250 1.9 2.9 <3.5 1.1 13.2 49
J-3 17.7 7.69 27.3 0.08 36.8 5.3 10.1 1.83 149 7.5 14.1 19.9 11.0 255 2.5 3.9 5.3 1.2 1.5 47
CWS-A 18.7 7.48 29.1 0.76 39.0 5.7 11.4 2.76 182 8.6 19.5 20.9 13.2 303 <0.5 5 <3.5 0.4 <1.5 49
CWS-B 18.5 7.55 28.7 0.44 39.5 5.7 11.5 2.78 185 8.3 17.6 20.7 12.7 303 0.8 2.1 3.6 4.8 347 50
NWS 14.1 7.75 24.4 0.05 34.2 4.9 8.7 1.36 146 6.9 14.5 17.6 11.2 246 3.7 2.3 <3.5 0.2 3.3 41
WWS 15.9 8.04 20.4 0.13 26.8 4.2 7.8 1.26 114 7.5 4.4 18.9 8.7 194 <0.5 <2.0 <3.5 <0.1 <1.5 44
WHO (2004) - 6.5-9.5 - - - - - - - - 50 - - 1000 200 10p - 400 - -
MOH & ASC
(2006) - 6.5-8.5 - - - - 200 - - 250 - 250 - 1000 200 10 300 100 1000 -
Appendix VII: Information on some chemical quality parameters (apart from Appendix VI) of tap water in Lhasa City
Parameter State Remark Parameter State Remark
F- < 0.2 mg/L Cu < 1.8 µg/L Except H-1, 30 µg Cu/L
PO43- < 4.0 mg/L Hg 0.002-0.03 µg/L
TDP < 0.01 mg/L Except A and B, about 0.02 mg P/L Mo < 0.6 µg/L
Cd < 0.4 mg/L Ni < 0.9 µg/L Except H-1, 2.9 µg Ni/L
Co < 0.7 µg/L Pb < 4.2 µg/L
Cr < 0.8 µg/L Ti < 0.2 µg/L
75
Appendix VIII: LSIa, RSIa and measured water pH value (in the present study) of tap water in Lhasa City
Sample pH LSI State RSI State Sample pH LSI State RSI State
A-1 7.65 -0.05 C 7.8 C Continued from the left side
A-2 7.57 -0.12 C 7.8 C F-3 7.78 0.04 SF 7.7 C
A-3 7.54 -0.15 C 7.8 C G-1 7.46 -0.07 C 7.6 C
B-1 7.70 0.26 SF 7.2 C G-2 7.45 -0.12 C 7.7 C
B-2 7.82 0.52 SF 6.8 No
difficulties
G-3 7.40 -0.20 C 7.8 C
B-3 7.59 -0.11 C 7.8 C H-1 7.75 0.06 SF 7.6 C
C-1 7.72 0.05 SF 7.6 C H-2 7.75 0.06 SF 7.6 C
C-2 7.58 0.05 SF 7.5 C H-3 7.74 0.07 SF 7.6 C
C-3 7.47 -0.06 C 7.6 C I-1 7.90 0.08 SF 7.7 C
D-1 7.76 -0.15 C 8.1 C I-2 7.89 0.07 SF 7.7 C
D-2 7.73 -0.14 C 8.0 C I-3 7.89 0.07 SF 7.7 C
D-3 7.80 -0.04 C 7.9 C J-1 7.53 -0.07 C 7.7 C
E-1 7.50 -0.03 C 7.6 C J-2 7.60 -0.04 C 7.7 C
E-2 7.47 -0.01 C 7.5 C J-3 7.69 0.07 SF 7.5 C
E-3 7.48 -0.02 C 7.5 C CWS-A 7.48 -0.04 C 7.6 C
F-1 7.64 -0.12 C 7.9 C CWS-B 7.55 0.05 SF 7.5 C
F-2 7.72 -0.01 C 7.7 C NWS 7.75 0.10 SF 7.6 C
To be continued at the right side WWS 8.04 0.19 SF 7.7 C
a Tchobanoglous & Schroeder, 1987; LSI: Langelier saturation index; RSI: Ryznar stability index; LSI = pHmeasured – pHsat; RSI = 2pHsat – pHmeasured; pHsat = pH of the water in equilibrium with solid CaCO3
= ‐ log ([ ] [ ]
)sp
HCOCa
K
HCOCaK −+−+ 3
22
32 γγ
Where, +2Caγ and −
3HCOγ is the activity coefficients for Ca2+ and HCO3‐, respectively.
When, LSI > 0 water is scale‐forming (SF) (supersaturated with respect to CaCO3) LSI = 0 water is neutral LSI < 0 water is corrosive (C) (undersaturated with respect to CaCO3)
When, RSI < 5.5 heavy scale will form 5.5 < RSI < 6.2 scale will form 6.2 < RSI < 6.8 no difficulties 6.8 < RSI < 8.5 water is corrosive (C) RSI > 8.5 water is very corrosive
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