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 (2009) 6242–6254

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Water quality in the Tibetan Plateau: Major ions and trace elements in the headwaters of four major Asian rivers Xiang Huang a,b,⁎, Mika Sillanpää a, Egil T. Gjessing c, Rolf D. Vogt c a b c

Laboratory of Applied Environmental Chemistry, University of Kuopio, Patteristonkatu 1, FIN-50100 Mikkeli, Finland Department of Chemistry and Environmental Sciences, Tibet University, No. 36 Jiangsu Lu, Lhasa, T.A.R. 850000, PR China Department of Chemistry, University of Oslo, P.O. Box 1033, Oslo 0315, Norway

a r t i c l e

i n f o

Article history: Received 10 May 2009 Received in revised form 29 August 2009 Accepted 1 September 2009 Available online 23 September 2009 Keywords: Major ions Trace elements Water quality Climate change Major Asian Rivers Tibetan Plateau

a b s t r a c t The Tibetan Plateau covers an area of about one fourth of Europe, has an average elevation over 4000 m above sea level, and is the water sources for about 40% of world's population. In order to foresee future changes in water quality, it is important to understand what pressures are governing the spatial variation in water chemistry. In this paper the chemistry including major ions and trace elements in the headwaters of four major Asian rivers (i.e. the Salween, Mekong, Yangtze River and Yarlung Tsangpo) in the Tibetan Plateau was studied. The results showed that the content of dissolved salts in these Tibetan rivers was relatively high compared to waters from other parts of the world. The chemical composition of the four rivers were rather similar, with Ca2+ and HCO− 3 being the dominating ions. The exception was the Yangtze River on the Plateau, and Li due to silicate weathering followed by strong evaporation which was enriched in Na+, Cl−, SO2− 4 caused by a negative water balance, dissolution of evaporites in the catchment and some drainage from saline lakes. The concentrations of heavy metals (Cu, Co, Cr, Ni, Cd, Pb, and Hg) and As, NH+ 4 were generally low in all the rivers. Anthropogenic impacts on the quality of the rivers were identified at a few locations in the Mekong River and Yarlung Tsangpo basins. Generally, the main spatial variation in chemical compositions of these under studied rivers was found to be governed mainly by difference in geological variation and regional climatic-environment. Climate change is, therefore, one of main determining factors on the water chemical characteristics of these headwaters of Asian major rivers in the Tibetan Plateau. © 2009 Elsevier B.V. All rights reserved.

1. Introduction The Tibetan Plateau is called the “Water Tower of Asia” as it is the source of the ten largest rivers in Asia, which are the water sources for about 40% of world's population. Within the Plateau there are more than 100 rivers that have catchments area over 2000 km2, among them 20 rivers that have drainage areas exceeding 10,000 km2 (Guan and Chen, 1980; He and Feng, 1996). The Plateau is endowed with more than 1600 natural lakes of area greater than 1 km2, five of which exceed 1000 km2 in surface area. Notably, more than 350 are saline lakes of various types (Zheng, 1997). The Tibetan Plateau is also renowned for its numerous high mountain chains, with the Kunlun Mountains in the north, the Tanggulha Mountains in the northeast, the Hengduan Mountains in the east, the Gangdies Mountains and the Nyenchentangla Mountains stretching from the west across centre towards southeast, and finally

⁎ Corresponding author. Department of Chemistry and Environmental Sciences, Tibet University, No. 36 Jiangsu Lu, Lhasa, T.A.R. 850000, PR China. Tel.: +358 403553709, +86 13518986066; fax: +358 153556363. E-mail addresses: xiang.huang@uku.fi, [email protected] (X. Huang), mika.sillanpaa@uku.fi (M. Sillanpää), [email protected] (E.T. Gjessing), [email protected] (R.D. Vogt). 0048-9697/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2009.09.001

the renowned Himalayas on the far south margin of the Plateau. Due to the high altitude numerous large continental and monsoon maritime glaciers exist in the region (Shi and Yang, 1985), constituting, in terms of mass, the third largest ice cover on earth (Barnett et al., 2005). The distribution of these numerous mountain glaciers is of great significance to the water resources. The Plateau, due to its role as major water source and its strong topographic relief, has been the subject of research on water resources and hydro-energy explorations (e.g. Guan and Chen, 1980; He and Feng, 1996; Liu, 1999). Despite its significance, there is a lack of knowledge and understanding regarding the water quality of these water resources. There is growing concern about the potential effects of global warming and resultant changes in hydrological conditions on the availability and quality of the water from the Plateau (e.g. Barnett et al., 2005). One of these concerns is related to the release of accumulated long-range transported pollutants from the melting glaciers (Huang et al., 2008). In order to foresee future changes in water quality we need to understand what pressures are governing the spatial variation in water chemistry. Only a few studies on water chemistry in the Himalayan rivers have focused on climatic factors (temperature and precipitation), chemical weathering and physical erosion, as well as CO2 consumption and carbon system circulation (Harris et al., 1998; Colin et al., 1999; Galy and

X. Huang et al. / Science of the Total Environment 407 (2009) 6242–6254

France-Lanord, 1999; Dalai et al., 2002; Kısakűrek et al., 2005; Liu et al., 2005; Singh et al., 2005; Hren et al., 2007). Recent studies of surface water quality in the Tibetan rivers have reported elevated levels of heavy metals (such as Hg, Cd, Ni, Cu) (Li et al., 2007; Huang et al., 2009, mining impact on the water quality in Tibet, unpublished work). These contaminations were believed to be due to local mining industry. In saline lakes high concentrations of heavy elements, such as Pb and As, are also found. This is, however, likely due to natural processes (Yu, 1992; Zheng, 1997). In the present work, the water quality of four major rivers: the Salween River, Mekong River, Yangtze River, and the Yarlung Tsangpo (Brahmaputra) on the Tibetan Plateau is studied. New information on major ions and trace elements in these waters at their source in the Tibetan Plateau is presented. 2. Materials and methods The Tibetan Plateau, within the Tibet Autonomous Region (T.A.R., China), occupies an area of 1.22 million km2. It has an average elevation above 4000 m above sea level (a.s.l.), gradually sloping from the northwest downwards to the southeast. The typical weather type on the Plateau varies from arid to semi-arid in the upper northwest to the central part of the Plateau, to subtropics in the lower southeast parts of the Plateau. The dominant vegetation types 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 river valleys at the east and southeast margins of the Plateau. The West and Northwest parts of the Plateau are shielded by the high mountains along its south margin (Shi and Yang, 1985). 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 variation ranges from 10.0 °C in the south to 17.5 °C in the north. Due to the effect of monsoon and topography the regional distribution of precipitation is uneven, with mean annual precipitation varying from only 74 mm in the northwest to 802 mm in the southeast. More than 80% of the rain falls between May and September (ECLCT, 2005). The Plateau is subject 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 4000 to 8000 MJ/m2 and annual sunshine duration is between 1500 and 3500 h on the Plateau, with an increasing tendency from the southeast to the northwest. This causes evaporation to significantly exceed rainfall on the Plateau. The annual Pan evaporation varies from 1186 to 2800 mm from the southeast to the northwest (ECLCT, 2005). This is coincident with the annual aridity that reaches a maximum of 100 in the north-western part of the Plateau (Zheng, 1997). 2.1. Sampling locations Stream water samples were collected from the centre to the east margin, and to the southeast edge of the Plateau in T.A.R., Sichuan Province, and Yunnan Province of China (Fig. 1, Maps 1 and 2). Sampling stations (St.), located both in remote and urban areas, were selected with the aim to span a topographic relief from 4300 m to 1700 m a.s.l. and to cover the water course of the four main rivers and their major tributaries as described below. The water flowing through major cities and towns, such as Lhasa, Zetang, Bayi, Chamdo, Nyarong (Xinlong), Litang, Batang and Gyetang (Zhongdian), are covered by the sampling program (Fig. 1, Maps 1 and 2). An important selection criterion was also to obtain samples which could be compared to a previous study (Huang et al., 2008). Remote location or limited access due to e.g. deep gorges with high flow rate or sharp river shore sides, made the desired sampling unachievable in some cases. Salween River (Gyalmo Ngulchu in Tibetan; Nu-jiang in Chinese) is the second longest river in Southeast Asia (Table 1) and one of only two

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large non-regulated rivers left 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 its 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 reaches in the west Yunnan province, where subtropical and tropical evergreen conifers dominate. The river drains 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). Only a limited number of accessible sampling locations (see Fig. 1, Map 2) were found and these were comprised along a short stretch below the confluence of its tributary Lengchu. The upstream basin from these sampling sites 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 ophiolitic1 and undivided ultrabasic rocks (ISSAS, 1986; Wu et al., 2008a). To the east the Yuchu runs parallel to the Salween River through the vast Pomda pasture before they merge. The Yuchu is the biggest contributor to the Salween River on the Plateau. Mekong River (Dzachu in Tibetan; Lancang-jiang in Chinese) is the seventh longest river in Asia (Table 1). The river is closely bordered to the west by the Salween River and to the east by the Yangtze River (Fig. 1, Maps 1 and 2). As for the majority of the river catchments on the Plateau, the watershed of the Mekong River is located within the semi-arid monsoon climate zone. The dominant forms of vegetation are alpine steppes and meadows in the north, and alpine shrub and subtropical forests in the south. The soils in these three parallel river basins are weathered mainly from sedimentary sandstone and shale (ISSAS, 1986). Low-grade metamorphic rocks, granitoid intrusive rocks, clastic rocks and limestones are exposed in the river catchment from Chamdo down to the lowest sampling location (St. 6, see Fig. 1, Map 2). The headwater source areas are made up clastic rocks, limestones and volcanic rocks (ISSAS, 1986; Wu et al., 2008a). The three parallel rivers run in the southeastern Plateau to the west of Yunnan Province, 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 Mekong River ends its journey in the South China Sea of the Pacific Ocean. Dzachu is the major headwater of the Mekong River. It runs some 518 km before it merges with Ngomchu (346 km) in Chamdo to form the Mekong River (Chamdo in Tibetan means “join of waters”) (Fig. 1, Maps 1 and 2). Yangtze River (Drichu in Tibetan; the upper reach in Chinese is called Jinsha-jiang) is the longest river in Asia and the third longest in the world (Table 1). It ranks fourth in the world in terms of total water discharge to the sea (Chen et al., 2002) draining nearly 1/5 of China. It starts from the Geladandong glacier (6 621 m a.s.l.) at the Tanggulha Mountains and flows first southwards on the Plateau, makes a large bend at Shigu town in Yunnan Province (Fig. 1, Map 2) and then flow eastwards until it runs out in the East China Sea of the Pacific Ocean. 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 catchment (Hu et al., 1982; Chen et al., 2002; Wu et al., 2008a,b). Along the river down to Shigu town in west Yunnan the river basin is comprised of low-grade metamorphic rocks, clastic rocks, intermediatebasic volcanic rocks, granitoid intrusive rocks and some fractions of ophiolitic melanges2 (ISSAS, 1986; CWRC, 2007; Wu et al., 2008b). At the river catchments above Shigu town on the Plateau, the mean annual precipitation is about 450 mm (CWRC, 2007) and the annual evaporation loss is 2 to 6 times greater than annual precipitation (Zheng, 1997).

1 Section of the Earth's oceanic crust and the underlying upper mantle that has been uplifted or emplaced to be exposed within continental crustal rocks. 2 Large scale breccia, a mappable body of rock characterized by a lack of continuous bedding and the inclusion of fragments of rock of all sizes, contained in a fine-grained deformed matrix.

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Fig. 1. Map of sampling locations along the Salween River, Mekong River, Yangtze River, Yarlung Tsangpo and their tributaries in the Tibetan Plateau. Numbers refer to sampling station (St.) used in the text and other figures.

X. Huang et al. / Science of the Total Environment 407 (2009) 6242–6254 Table 1 Total length, mean annual surface runoff and catchments area of the Salween, Mekong, Yangtze River, and Yarlung Tsangpo. River

Length (km) In T.A.R.b

Total Salween River Mekong River Yangtze River Yarlung Tsangpo

c

3200 4500c 6300c 3350d

1393 509 509 2057

Mean annual surface runoff (billion m3)a

Catchments area (km2)

In Chinac

Total

70 74 975 165

In T.A.R.b 359 115 75 1395

In T.A.R.b c

325,000 810,000c 1.8 millionc 630,000e

102,500 38,300 23,060 240,480

a Mean annual surface runoff in China is considered as the annual mean value in the national terrene. Mean annual surface runoff in T.A.R. refers to the mean value at the T.A.R. border to other provinces or countries. b Guan and Chen (1980). c MWR, 2004. d Liu (1999). e Singh et al. (2005).

The vegetation types in the majority of the Yangtze River basin on the Plateau are alpine meadow, alpine shrub and forest. The Yangtze River is joined by a large number of tributaries. The predominantly snowmelt fed Batangchu was the most limpid river observed during the period of sampling. This is also reflected in a low turbidity. The Yalong River (1 640 km) is the biggest contributor to the main river in its headwaters region. 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). Litangchu is a small contributor of the Yalong River with a river course that passes through vast open pristine grassland. Litang county town (4014 m a.s.l.), one of the world's highest located towns, is the only major settlement along the Litangchu course (Fig. 1, Map 2). Yarlung Tsangpo (Brahmaputra; Tsangpo in Tibetan means big river) originates at above 5200 m a.s.l. from the Jemayangdrung glacier, near Mount Kailash in the northern Himalayas, and runs through the Gandise–Himalayan Tectonic Region in the southern Plateau (Fig. 1, Map 1). It is the biggest river on the Plateau, both in terms of length and drainage area (Guan and Chen, 1980) (Table 1). 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 finally ends up in the Bay of Bengal of the Indian Ocean. The upper part of the catchment is shielded from monsoonal rainfall by the Himalaya rain-shadow. As a result, alpine grasslands and arid farmlands are dominant. As the elevation gradually decreases, the climate zone changes. The lower part of the catchment on the plateau is densely forested. The bedrock in the drainage area on the Plateau consists mainly of granite/granitic gneiss, schist/other felsic volcanic, and mafic volcanics (includes amphibolites and other high-grade mafic metamorphics) (Hren et al., 2007). Ophiolites and ophiolitic melanges are widely exposed along the river basin (GMRT, 1993). Lhasa River (Kyichu), Nyangchu (Nyiyang He) and Parlung Tsangpo are the largest contributors to the Yarlung Tsangpo in the central and southern Plateau (Fig. 1, Map 1). With catchment areas covering 32,471 km2, 17,535 km2 and 28,631 km2, they flow 551 km, 286 km and 266 km over the Plateau, respectively (He and Feng, 1996). Parlung Tsangpo is the biggest contributor in terms of water discharge to the Yarlung Tsangpo (Guan and Chen, 1980). The capital city of Lhasa, with a population of 182,000, is located on the north bank of Lhasa river. The Lhasa river valley is the most socioeconomically developed region on the Plateau. Bayi town, one of the most rapidly developing cities in the T.A.R., is located on the east bank of the Nyangchu. Although this river basin has a relatively high amount of precipitation (660 mm) (ECLCT, 2005), the river is mainly fed by snow melt water (Liu, 1999). Sampling was made difficult along the Yarlung Tsangpo because of road constructions and landslides along some part of the river. However, samples were achieved from 10 locations over a 560 km long stretch (Fig. 1, Map 1).

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2.2. Sampling, sample preparation and analysis Water samples were collected and in situ water temperature (temp.), pH, electrical conductivity (EC) and turbidity (turb.) measurements were made at 72 sampling stations along the four river main streams and their tributaries in the Tibetan Plateau (Fig. 1, Maps 1 and 2). The sampling was conducted during late summer 2007 (from 25th August to 13th September). Water samples were collected in 2 L polypropylene bottles as far from the stream-bank as possible and at approximately 30 cm below the water surface. After in situ measurements, each collected sample was filtered through a 0.45 µm disposable cellulose acetate syringe membrane filter (33 mm diameter, white rim, Whatman GmbH, Germany). The filtered samples were divided into three portions: (I): 15 mL into polypropylene (PP) bottles (pre-acid-washed with 10%, v/v, nitric acid 65% Suprapure®, MERCK, Germany) for metal analysis; (II): 100 mL into polyethylene (PE) bottles (pre-washed with deionized water) for anion and other parameter determinations; and the third potion (III) sufficient to fill up borosilicate glass (BG) bottles (16 × 125 mm) for Hg determination. PP/PE and BG sample bottles were capped immediately with polyethylene and Teflon screw caps, respectively. Water samples were then stored in double polyethylene plastic bags and kept at 4 °C until analysis. In situ measurements for pH, EC and water temp. were carried out by applying a portable pH meter with accuracy ± 0.02 pH units (Waterproof pHScan 3+ Tester, 0.00–15.00 pH, Eutech Instruments Pte Ltd, Singapore) and a portable EC meter (accuracy: ± 1% of full scale) with temperature sensor (accuracy: ± 0.5 °C) (Waterproof ECTestr low+, 0–1999 µS/cm, Eutech Instruments Pte Ltd, Singapore), respectively. A portable turbidity meter with accuracy ± 2% (Model 2100P ISO, ©Hach Company, USA) was applied for turb. measurements. Water samples for dissolved metal concentrations, i.e. Calcium (Ca2+), sodium (Na+), potassium (K+), magnesium (Mg2+), aluminium (Al), arsenic (As), copper (Cu), iron (Fe), lithium (Li), manganese (Mn), molybdenum (Mo), titanium (Ti), zinc (Zn), cadmium (Cd), cobalt (Co), chromium (Cr), nickel (Ni), lead (Pb), and dissolved sulphur (S) were acidified to pH < 2 with HNO3 (65% conc., Suprapure®, MERCK, Germany) and quantified by Inductively Coupled Plasma — Atomic Emission Spectroscopy (ICP-AES, iCAP 6300 Duo View ICP-AES spectrometer, Thermo ELECTRON CORPOATION, UK) at the Laboratory of Applied Environmental Chemistry, University of Kuopio. Dissolved mercury (Hg) concentration was determined by Flow Injection Atomic Absorption Spectrometry (FI-AAS) at the Viljavuuspalvelu Oy (Soil Analysis Service Ltd), Mikkeli, Finland. Dissolved phosphorus (TDP) was analyzed using the molybdenum-antimony spectrophotometric method after nitric-perchloric acid oxidation (SEPA, 2002). Dissolved SiO2 was measured using an Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES, OptimaTM5300DV, PerkinElmer) at The State Key Laboratory of the Tibetan Geology & Mineral Exploration and Development Bureau in Lhasa. Dissolved nitrogen (TDN), was analyzed as nitrate by a Non Dispersive Infrared Detector (Multi N/C 3000, Analytik Jena AG, Germany) after a thermocatalytic oxidation. Dissolved anions, i.e. Chloride (Cl−), 2− + nitrate (NO− 3 ), sulphate (SO4 ) and ammonium (NH4 ) were determined by Ion Chromatography (IC, 790 Metrohm Personal IC, Metrohm Ltd., CH-9101 Herisau, Switzerland) at the Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing. Bicarbonate (HCO− 3 ) was determined by charge balance from the other ions. This method has been shown to be reliable to within 10% in Himalayan rivers and other major rivers draining the Tibetan Plateau (Galy and FranceLanord, 1999; Bickle et al., 2003; Wu et al., 2008a). Blank and duplicate sample analyses according to standard operating procedures were performed on about 10% of all samples. Analytical results for major ions (except NO− 3 ) as well as Al, Li, Mn and S compared favorably to original results (average R2 = 0.97). However, the rest of elements, possessing relatively low concentrations, showed higher variability between original and replicate samples. The accuracy

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X. Huang et al. / Science of the Total Environment 407 (2009) 6242–6254 − of all anions, followed by SO2− 4 (20–40%). As the exception, Cl accounts for about 45% in the Yangtze River main stream, while in other river basins the Cl− proportion only constitutes 10% of the anionic charge. Water in the Yangtze River has a significantly higher content of Na+ and Cl−, compared to the other rivers studied here (Fig. 2).

of the ICP-AES method was evaluated by analysis of mono-component element reference solutions (ROMIL PrimAg®-plus certified reference material, ROMIL Ltd., UK). The average recovery of the quality control analysis was 99 ± 4% depending on the actual element and its concentration. The method's precision was estimated by duplicate analyses of the standard reference materials. The relative standard deviation (RSD) of most measurements was <2%, indicating a good precision of the applied method. The exceptions were for As and Cu (which in general have rather low concentrations), with RSD of 10%. An overall good measure of the quality of the data presented here is the good correlation between calculated TDS (HCO− 3 and SiO2 excluded) and measured EC (R2 = 0.9802), and also between the calculated EC and measured EC (R2 = 0.9959).

3.2. The rivers Some quality parameters of the four rivers are illustrated on Fig. 3. Average pH for each stream was basically the same (pH=8.4) and turbidity of all waters was high. More than 35% of the turbidity measurements were above 1000 NTU (Table A1). Yangtze River had the highest content of dissolved salts. This finding is clearly shown by both elevated EC and high content of TDS, especially the content of Na+, Cl−, Li and NO− 3 , which were higher in the Yangtze River compared to in particular Yarlung Tsangpo and Salween River. It should be noted that the Mekong River was high in particulate matter, with 42% of the samples from this river having turbidity above 1000 NTU. Analytical results for each river catchment are described in the following paragraphs.

3. Results The analytical results of the four selected rivers and their tributaries are grouped relative to their drainage areas and depict from upstream to downstream in Tables A1 and A2 (Appendix A). Concentrations of some contaminants, i.e. Cu, Co, Cr, Ni, Cd, Pb, Hg, As and NH+ 4 in the rivers were below those of Chinese National Environmental Quality Standards for surface water quality (SEPA&AQSIQ, 2002) and the World Health Organization (WHO) guidelines for drinking water quality (WHO, 2004). In most samples these elements were even found to have concentrations below the detection limits for the applied methods. These elements are, therefore, not included in further considerations, except for As in Batangchu and Ni in Kyemtangchu. 3.1. Major ion composition Mean values of concentration of selected major ions in the four rivers are shown in Table 2. These values are compared with similar data from other parts of the world. It is apparent that the content of total dissolved 2− salts [TDS = ∑ (Ca2+ + Na+ + K+ + Mg2+ + Cl− + NO− 3 + SO4 + + SiO )] is relatively high in most of the Tibetan waters. This is HCO− 3 2 in particular the case of the Yangtze River and the Mekong River. The relative proportions of major cations on an equivalent basis are plotted in ternary diagrams (Fig. 2a). This plot shows that with the exception of the Yangtze River main stream, all rivers are located in the Ca2+ corner. On average, Ca2+ accounts for 50–70% of all cations, followed by Mg2+ (20–27%), Na+ (7–27%) and K+ (1%). In the Yangtze River main stream, Na+ accounts for up to 40% of the total cation budget, which is on average four times higher than that of other rivers (Table 2). Anionic composition illustrated in Fig. 2b shows that HCO− 3 constitutes the major proportion of anions in practically all waters. The exceptions are the one sample from Keymtangchu (St. 81; Fig. 1, Map 1), with unusual high sulfate levels (1715 µeq/L), followed by all samples from the Yangtze River main stream with high chloride concentrations, ranging from 1566 to 4402 µeq/L. On average, HCO− 3 accounts for 50–60%

3.2.1. Salween River Only a relatively small part of the main Salween River was included in this study. This was the 9 km long part of the river downstream from the conjunction with Lengchu (St. 55–57, Fig. 1, Map 2). From the results shown on Table A1, it appears that the quality of Lengchu was rather different from the main river, with higher content of NO− 3 , TDP, Fe and Zn (St. 58 and St. 60–62, Fig. 1, Map 2). However, the elevated concentrations of Lengchu were generally too low to be of any significant ecological importance and the data do not show that this tributary had an impact on the chemical quality of the main river. The upper part of the contributor Yuchu was studied along a 52 km stretch downstream from Pomda Airport (Fig. 1, Map 2). From the upper (St. 52) to the lower sampling point (St. 54) almost no changes in the content of major dissolved ions were found. However, the results clearly demonstrate a gradual increase in particulate matter, with turbidity increasing from 70 NTU to 177 NTU. The Salween River main stream was found to have a relatively high content of total dissolved ions, dominated by Ca2+, Mg2+ and HCO− 3 , compared to its tributaries Lengchu and Yuchu (Table A1). The main stream had also more than two times higher content of SO2− 4 compared to its tributaries. 3.2.2. Mekong River There were rather small changes in the water quality of the Mekong River downstream from Chamdo town. Comparing parameters such as 2+ and TDS (at St. 50) immediately (1 km) downstream the EC, SO2− 4 , Ca confluence of Dzachu and Ngomchu, with the composition some 500 km further downstream (at St. 6; see Fig. 1, Map 2) (descending in elevation more than 1500 m), we found only a 15% to 23% decrease

Table 2 Composition of the Salween River, Mekong River, Yangtze River, and Yarlung Tsangpo in the Tibetan Plateau (mean values of all samples in the catchments) compared to river and 2− − lake waters around the world. Here, TDS = ∑ (Ca2+ + Na+ + K+ + Mg2+ + Cl− + NO− 3 + SO4 + HCO3 + SiO2 in mg/L). EC is in mS/m. Rivers a

Salween River Mekong Rivera Yangtze Rivera Yarlung Tsangpoa Europe b Asia b Africa b North America b South America b World b a b c

Ca2+

Mg2+

Na+

K+

HCO− 3

SO2− 4

24 49 40 21 31 18 13 21 7 15

7 14 12 4 6 6 4 5 2 4

3 12 38 3 5 6 11 9 4 6

1 1 2 1 2 4 – 1 2 2

66 138 108 47 95 79 43 68 31 58

31 69 53 27 24 8 14 20 5 11

Measured in the present study. Wetzel (1975). Calculated according to Wetzel (1975).

Cl− 5 14 64 5 7 9 12 8 5 8

NO− 3

SiO2

TDS

EC

0 0 0 0 4 1 1 1 1 1

4 4 5 4 8 12 23 9 12 13

141 302 324 112 182 142 121 143 69 120

18 37 44 15 31 24 21 25 12 20

c c c c c c

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− 2− Fig. 2. Ternary plots of the dissolved major cations a: (Mg2+, Na+ + K+ and Ca2+) and major anions b: (HCO− 3 , Cl and SO4 ) on an equivalent concentration (µeq/L) basis in the + and Cl− also constitute a significant proportion. studied rivers. In general, Ca2+ and HCO− 3 are by far the dominant in all the waters, except in the Yangtze River where Na

2+ (EC = −23%, SO2− = −18%, and TDS= −19%). The 4 = −15%, Ca exception was for the content of Al which showed a small increase during this 500 km long distance (from 9 µg Al/L to 22 µg Al/L). The quality of the two contributors, Dzachu and Ngomchu was only slightly different from the main river. The content of almost all major chemical components in Dzachu showed an increase downstream: TDS in this contributor doubled along the 90 km long part of the river down to Chamdo town (from St. 44 to St. 46, Table A1). This was mainly due to a significant increase (~5 times) in Na+, Cl− and SO2− 4 concentrations. No municipal wastewater treatment facilities existed in the region. The town of Chamdo, with its 31,000 inhabitants, discarded therefore all its wastes (both liquids and solids) into the river without treatment. An influence of sewage effluents might also be seen in the nutrient status of the water, as the TDN in Dzachu and Ngomchu (St. 46 and St. 48) just before Chamdo is 0.30 mg N/L and 0.36 mg N/L, respectively; however,

after mixing, downstream of Chamdo (at St. 47) the TDN was increased seven times (to 1.54 mg N/L), which was the highest value in all samples measured in this study. 3.2.3. Yangtze River The content of TDS in the Yangtze River, especially upstream from the Batangchu confluence, was clearly different from other rivers, elevated concentrations of Ca2+, Mg2+, Na+ and Cl− being the major cause for the high TDS (Fig. 3 and Table A1). TDS in the uppermost sampling site near Derge (St. 26) was 0.5 g/L. This salt content was reduced to about a half at 800 km downstream in Shigu (at St. 1; Fig. 1, Map 2), with a difference in elevation of about 1400 m. The contribution of SO2− 4 (and therefore also S, Table A2) to the anionic charge-budget in the Yangtze River was also significant. In addition to the high content of the salts described above, a relatively high concentration of Li (Fig. 3) should be emphasized. Fig. 4

Fig. 3. Chemical quality of the four major rivers, i.e. the Salween River, Mekong River, Yangtze River, Yarlung Tsangpo and their tributaries in the Tibetan Plateau, given as mean values. n: refers number of samples considered.

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shows a gradual decrease in concentration of major water quality parameters in the Yangtze River from Derge down (St. 26) to Shigu town (St. 1). Even though the results show a clear dilution downstream (except HCO− 3 ), it should be noted that this water remained extremely high in dissolved salts. The main river downstream of the Kamtok village flowed gently approx. 50 km through a narrow valley down to St. 25. Along this stretch the concentrations of dissolved salts, in particular Mg2+ − (20 mg/L), Na+ (87 mg/L), SO2− 4 (103 mg/L), Cl (156 mg/L) (Table A1) and Li (74 µg/L, Table A2), reached the highest value (at St. 25) measured in the present study (Fig. 4). By comparing the mean values of the Yangtze River main stream with data from its downstream tributary Batangchu (St. 15 and 16), it is apparent that this part of the catchment area gave rise to a more dilute runoff relative to the catchments further upstream. However, despite the relatively dilute character of the water, the Batangchu tributary contained the highest content of As found in the study (avg. 12 µg As/L; Table A2). This value slightly exceeds the established health-based guideline value for drinking water, set by both the WHO (WHO, 2004) and Ministry of Health of the PR China (MOH) and Standardization Administration of the P.R. China (MOH & SAC., 2006) (10 µg As/L). The Yalong River meets with the Yangtze River around 1200 km downstream from Kamtok (Fig. 1, Map 2). There were three sampling stations from the mid part of Yalong River around Nyarong county town (Xinlong xian in Chinese) (Sts. 18–20). Unfortunately, no sample was collected after the Yalong River merged into the main river, where it causes the discharge of the main river to double (Wu et al., 2008b). The measured results show only minor differences along this approx. 100 km part of Yalong River. Nevertheless, this river (avg. 237 mg TDS/L) was a more significant contributor than Batangchu (107 mg TDS/L) to the elevated TDS concentration in the Yangtze River (Table A1). 3.2.4. Yarlung Tsangpo The part of Yarlung Tsangpo that was studied here included the main river as well as its tributaries Lhasa River, Kyemtangchu, Nyangchu, and finally Parlung Tsangpo in the southeastern Plateau. Ten samples in total

from 560 km long part of the Yarlung Tsangpo between the conjunction with Lhasa River and the contributing Nyangchu in the southeastern Plateau (Fig. 1, Map 1) were included in the present study. The result shows a gradual decrease in concentration of major ions with a linear descent in elevation from 3600 m a.s.l. to about 3000 m a.s.l. (Table A1). The mean chemical quality of Yarlung Tsangpo river water is illustrated in Fig. 5 together with the corresponding data for its tributaries: Lhasa River, Kyemtangchu, Nyangchu and Parlung Tsangpo. There was no major difference in water quality between the main river (Yarlung Tsangpo) and its major tributary, Lhasa River. However, this tributary was more dilute with the exception of NO− 3 and Fe, Al and Zn (Table A2), Lhasa River showed a relatively mild gradual decrease of concentration of major ions downstream over the first 25 km, from 130 mg TDS/L (at St. 85) to 121 mg TDS/L (at St. 84). The discharge from Lhasa city, with its 182,000 inhabitants, had an insignificant impact on the water quality of this river. Slightly elevated TDS and turbidity downstream to Lhasa may have originated from the city itself as TDS increased only 7% after the city and turbidity changed from 84 NTU to 95 NTU before and after the city. The Kyemtangchu tributary seemed more likely to have had some influence on the main river as its mean water chemistry showed a higher concentration of major ions as well as the highest concentrations of Ni (avg. 51 µg/L, Table A2), Zn (avg. 11 µg/L) and Mn (avg. 153 µg/L) measured in the present study (Fig. 5 and Table A2). The elevated concentrations of Ni and Mn exceed the established health-based guideline value for drinking water, set by the MOH & SAC (20 µg Ni/L and 100 µg Mn/L). However, the data do not show an influence on the chemical quality of the main river (Yarlung Tsangpo) downstream (St. 80). The Nyangchu tributary, some 300 km further downstream from the Kyemtangchu confluence, represented the “cleanest” and most dilute water encountered in the present study (avg. TDS= 58 mg/L, Fig. 5). Both Nyangchu and Parlung Tsangpo are mainly fed with snowmelt water and well developed maritime glaciers in the watershed and the water quality of these two rivers was comparable with low chemical fluxes along the river course. However, a higher content of NO− 3 and especially that of Al and Fe was observed in Parlung Tsangpo (Fig. 5).

Fig. 4. Changes in chemical composition of Yangtze River from Derge (near St.26, “zero-point”) and downstream 800 km to Shigu town (St.1). Kamtok village is about 60 km from the “zero-point”. The confluence of Batangchu to the Yangtze River is about 360 km from the “zero-point” and Shigu town is about 800 km from the “zero-point”. Corresponding sampling station (St. No.) is labeled on each data point of chloride (Cl−) concentration trendline.

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Fig. 5. Mean values of chemical water quality of Yarlung Tsangpo and its contributors, Lhasa River, Kyemtangchu, Nyangchu and Parlung Tsangpo. n: refers number of samples considered.

The TDS levels of the river Yarlung Tsangpo ranged from 106 to 165 mg/L with the mean shown in Fig. 5. Highest TDS concentration (165 mg/L) along the river was found in its upper reaches (St. 97), upstream of the Lhasa River confluence (Table A1 and Fig. 1, Map 1). 4. Discussion In general, river water chemistry is to a large degree reflected by the soil constituents in the catchments. Although human activity plays a role, the trace element concentrations in Tibetan stream waters are mainly governed by the weathering of soil parent materials followed by upconcentration due to high aridity (Tian et al., 1993; Zhang et al., 2002). The Tibetan Plateau is the youngest and highest plateau in the world. In general, soils on the Plateau are therefore in general weakly developed and the soil organic matter scarce and weakly correlated with trace element amounts in the soils (Zhang et al., 2002). Chemical weathering and physical erosion of the soil parent materials on the Plateau provide a significant contribution to the chemical composition of its water. The Himalayan region has a high rate of chemical weathering and physical erosion (Colin et al., 1999; Dalai et al., 2002; Singh et al., 2005), while the interior of the Plateau, such as the headwater regions of the Salween River, Mekong River, and Yangtze Rivers, suffer mainly from physical erosion (Wang et al., 2007; Zhang et al., 2007). The rate of chemical weathering of e.g. feldspar and mica is sensitive to temperature. Meteorological studies have shown that over the last 40 year period (1960–2000) the mean annual temperature has risen by 0.8 °C (Du, 2001) on the Plateau. In addition, the Plateau's annual amount of precipitation (from the 1970 s to the1990s) has increased at a rate of 19.9 mm per decade (Du and Ma, 2004). Global climate change is therefore believed to be one of the main determining factors of increased chemical weathering and erosion in the region (Colin et al., 1999; Dalai et al., 2002; Liu et al., 2005; Singh et al., 2005; Wang et al., 2007). Moreover, land-use changes in headwater areas and degradation of grassland on the Plateau are other major factors affecting the intensity of physical weathering and erosion, and thereby the water quality (Wang et al., 2007; Zhang et al., 2007). Mechanisms governing the chemical composition of these waters were assessed by identifying interrelationships and identifying covariations of parameters, using a Principal Component Analysis (PCA) (Minitab® 15.1.1.0., ©2007 Minitab Inc.). This analysis was based on the 72 samples that had data for the complete set of 24 parameters measured. As these samples are from four individual streams, the

problem with interdependencies within each stream is unavoidable and poses a clear limitation to the interpretation of the statistical results. Keeping this in mind the PCA still provides a clarifying view of the parameter interrelationships. Despite considerable parameter variations among individual samples, the first two principal components (PC1 & PC2) of the PCA represent 59% of the total variances in the data of the four rivers and their tributaries. The resulting PC loading-plot (PC2 vs PC1) is presented in Fig. 6. Three main parameter clusters can be observed in this figure. (S). The coCluster 1 consists of EC, Na+, K+, Li, Cl−, and SO2− 4 location of these parameters can be explained by the fact that various kinds of evaporites are present in the Plateau. The level of these major ions is also strongly governed by up-concentration, due to evaporation in the headwater lakes, and dilution downstream. Studies by Singh and co workers (2005, 2006) indicated that the majority of the dissolved salts in the Tibetan rivers are derived from various evaporites, salts and saline lakes. The co-location of Na+ and Cl− in the PCs- plot may also be due to dissolution of evaporite mineral, such as halite, in the catchments. Kısakűrek et al. (2005) demonstrated that approximately 90% of dissolved Li loads in the Himalayan rivers are derived from silicate weathering, even in the carbonate-dominated catchments. Nevertheless, unlike the Himalayan rivers, high content of Li-bearing minerals in a geothermal zone (~107 mg Li/L) (Zheng, 1997) that passes through the river basin and down into the stream, in addition to dissolution of evaporites, is most likely to be the source of the high content of Li found in the studied rivers. High concentrations of Li were, however, not observed in the previous study conducted during the spring low flow can be derived from either period (Huang et al., 2008). The SO2− 4 dissolution of gypsum (CaSO4) mineral in sedimentary evaporites or from oxidation of sulfide minerals (Galy and France-Lanord, 1999). Good and Cl− obtained in the Yangtze River correlation between SO2− 4 (R2 = 0.97) suggests that the primary source of SO2− 4 in this river is from evaporites, as is also observed by other studies (e.g. Chen et al., 2002; Wu et al., 2008b). This conclusion is supported by the presence of evaporites found in the upper part of the river catchments. However, the primary in the Yarlung Tsangpo was found to be from the source of SO2− 4 oxidation of sulfides (e.g. pyrite FeS2) present in the region (Galy and France-Lanord, 1999; Kısakűrek et al., 2005; Hren et al., 2007), since is not supported due to a lack of correlation evaporitic origin of SO2− 4 between Cl− and SO2− 4 . The clustering of pH and SiO2 together with HCO− 3 and Turb. in Cluster 2 (Fig. 6) indicates the breakdown of clay minerals, the major

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Fig. 6. Principal component analysis (PC2 vs PC1) of water quality-parameters of four major Asian rivers in the Tibetan Plateau. The first component (PC1) represents 47% of total variations; the second component (PC2) represents another 12% of total variations in all the data. Three clusters discussed in the text are also shown on the figure.

contributors of turbidity to the river. The pH value is clearly dictated 2+ by HCO− 3 in these rivers. Generally, on average, 85% of the solute Ca was balanced by HCO− 3 charge in the waters studied here, indicating that carbonate weathering was the main source for the solute Ca2+. Hren et al. (2007) suggested that 80–90% of dissolved Ca2+ and Mg2+ are generated from carbonate weathering in the Yarlung Tsangpo catchments. However, recent isotopic studies demonstrate that at least 50% of the Mg2+ is derived from silicate weathering in this river and other major Tibetan rivers (Tipper et al., 2006, 2008). Although the contents of these two base cations in the Yangtze River catchment downstream from the Plateau were also found to be mainly derived from carbonate weathering (Chen et al., 2002), Wu and co-workers (2008b) found that the river draining most of its length in the Plateau has a considerable high rate of silicate weathering. In the PCs-plot, Ca2+ and Mg2+ tend to depart from HCO− 3 and move towards cluster 1. This suggests that also up-concentration and dilution mechanisms along with weathering of other evaporite minerals (e.g. gypsum) might be important factors governing the levels of Ca2+ in these waters, whereas silicate weathering plays an important role in controlling the solute Mg2+ in these Tibetan rivers. Elements with comparably low solubility at the pH of these waters (Al, Fe, Mn, Ti and Zn) are located in cluster 3 (Fig. 6). These elements are, as commonly found, negatively correlated to pH along both PC1 and PC2. Generally, a tendency to decreasing ionic strength downstream can be observed. According to the sample score plot of the PCA (not shown), PC1 might be seen as to represent the spatial variation downstream of the individual watersheds. Although elevation per se is not an explanatory variable for the variations of chemical composition for the Tibetan waters, it may be conceived as a proxy for dilution and changes in climate (e.g., precipitation/evapotranspiration and vegetation, soil types and depths) along the topographic relief of the Plateau. The PC2 reflects more the geological variation within and among the catchments, especially regarding the carbonate content. The pH has therefore a strong loading along PC2. The temperature increase on the Plateau, due to global warming, is most pronounced in the headwaters areas of the Yangtze River. As a result, an increase in weathering and erosion intensity in the region can be expected. Rapid climate change has been found to be the major cause of ecosystem degradation in the headwaters area of the river (Wang et al., 2004). In this area, the remote sensing data obtained by Wang

et al. (2004) showed that over 15 years (from 1986 to 2000) lake water coverage have shrank by 11%, and alpine meadow swamps, which are sensitive to climate change, decreased by 28%. In addition, intensive deforestation and mineral exploration along the river basin can be observed. Where the vegetation cover is lost (desertification) the land suffers from wind erosion in addition to a high rate of water erosion. Even at the lower reaches of the river in Yunnan Province, despite rapid urbanization and input from industry (i.e., mining) to the river, water quality was found to be mainly influenced by soil erosion and terrestrial processes in the catchments (Zhang and Gu, 2000). However, a major contribution to the changes of the water chemical quality from human activity can be seen from the Yarlung Tsangpo basin (e.g. St. 97). The high content of dissolved salts found in the water is in agreement with other studies carried out in the same river (Chen, 1989; Hren et al., 2007). This is likely from discharge of high salinity lake water into the river from a hydropower station (some 20 km upstream from the sampling site). Chen (1989) assessed the impact of operation of this hydropower station (Yamdrok Yumtso hydropower station, 4440 m a.s.l.) on the water chemistry of the Yarlung Tsangpo, and showed an approx. doubling of the water salinity (measured as TDS) in the Yarlung Tsangpo stretching about 30 km downstream of the power station. Three in situ measurements made during previous sampling campaigns in spring 2006 from this lake showed that the lake had high conductivity (> 199.9 mS/m). The Yarlung Tsangpo and its tributaries supply the main agriculture region on the Plateau with water. Furthermore, more than half of the region's population is located along this water course, and the rapid economic development in Tibet has been centered along the river. Increased mineral exploration activities and processing is foreseen in the immediate future as the railway lines are planned to extend along the Yarlung Tsangpo River and its tributaries over the Plateau. In addition, being one of the most popular tourist destinations, now with convenient railway connection, the region has experienced a 60% growth in tourism in 2007. These rapid demographic changes and economic expansion will, in addition to the mining activities, put heavy burdens on the quality of the water in the region. Knowledge of water management as well as environment protection in general is poor in the Plateau. Furthermore, environmental regulations, such as solid waste and wastewater treatment, are relatively poorly implemented on the Plateau. This study shows that the headwaters of these Asian major rivers are still undisturbed at

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their source in the Tibetan Plateau, though in urban and industrialized areas human influence can be seen. Water quality degradation can be expected in the near future due to e.g. intensified weathering and erosion processes caused by global climate change and rapid development of mining operations in the region. 5. Conclusions This study provides rudimentary information on the overall regional span and spatial variations in chemical compositions of the important water resources on the Tibetan Plateau. The main purpose was to contribute to defining the present chemical quality of these Asian headwaters, seek to identify major natural factors governing this spatial variation and address possible sources for contaminants. The results showed that the content of dissolved salts in these Tibetan rivers is relatively high compared to waters from other parts of the world. The main spatial variation in chemical compositions is caused by differences in geological variation and climatic environment in the catchments. Climate changes and changes in land-use, such as deforestation, are therefore likely to have a strong impact on the chemical properties of these Tibetan rivers in the future. In general, the data suggests that the chemical fluxes in all the rivers are mainly controlled by carbonate weathering, with Ca2+ and HCO− 3 being the dominated ions. This is especially the case for the Salween River and Yarlung Tsangpo. Silicate weathering followed by strong evaporation and evaporite dissolution along with some drainage from saline lakes, contributing

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mainly high concentrations of Na+ and Cl−, plays in addition a significant role in controlling the chemical composition of the Yangtze River. With few exceptions, the Yangtze River main stream seemed to behave in a conservative way becoming more diluted downstream. The results obtained showed that most water bodies are considered to be undisturbed in respect to agriculture and other human activities, although a few locations with anthropogenic influence might be significant, especially from discharge of untreated municipal wastewater and mining activities.

Acknowledgements This study was funded by the EU and the city of Mikkeli, Finland. The Network for University Co-operation Tibet–Norway is acknowledged for financial support of the field work. The first author would like to thank Prof. Emeriti Hans Martin Seip and Dr. Thorjørn Larssen for their useful discussions on the data analysis. This manuscript has also benefited from insightful reviews by Sunil K. Singh and Albert Galy.

References Barnett TP, Adam JC, Lettenmaier DP. Potential impacts of a warming climate on water availability in snow-dominated regions. Nature 2005;438:303–9. Bickle MJ, Bunbury J, Chapman HJ, Harris NBW, Fairchild I, Ahmad T. Fluxes of Sr into the headwaters of the Ganges. Geochim Cosmochim Acta 2003;67(14):2567–84.

Appendix A Table A1 Major ion composition and TDN, TDP concentrations of the Salween River, Mekong River, Yangtze River, Yarlung Tsangpo and their tributaries in the Tibetan Plateau. St. No.

River

Elevation m

pH

EC

Temp.

Turb.

Ca2+

Mg2+

Na+

K+

SO2− 4

NO− 3

Cl−

HCO− 3

SiO2

TDN

TDP

TDS

mS/m

°C

NTU

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

Salween River basin tributaries and the river main stream 52 Yuchu 4282 8.4 15.9 11.7 53 Yuchu 4169 8.4 16.2 11.9 54 Yuchu 4116 8.4 16.5 12.5 62 Lengchu 3707 8.2 10.7 9.8 61 Lengchu 3108 8.4 14.0 11.0 58 Lengchu 2728 8.4 14.6 12.6 60 Lengchu 2728 8.3 15.3 12.6 57 Salween R. 2713 8.5 27.5 14.2 56 Salween R. – 8.4 26.7 14.4 55 Salween R. – 8.7 27.3 14.4

69.3 127 177 39.5 90.6 55.7 121 > 1000 > 1000 > 1000

21.1 21.3 21.9 14.9 18.7 21.0 21.4 32.1 32.8 32.1

5.3 5.3 5.6 2.3 3.0 2.8 3.3 12.7 12.3 12.6

1.8 1.8 2.0 2.9 4.1 3.4 3.4 4.3 4.0 4.2

0.6 0.6 0.7 0.6 0.7 0.6 0.7 1.1 1.0 1.1

20.6 20.2 19.4 13.9 21.6 24.8 34.9 53.0 53.2 52.0

0.46 0.35 0.46 0.57 0.41 0.44 0.27 0.26 0.07 0.03

4.3 4.3 4.3 4.6 4.7 4.8 4.9 4.9 5.2 4.9

62.7 63.6 68.4 39.8 47.9 47.8 38.8 98.7 97.2 99.2

3.6 4.1 4.0 3.8 4.1 4.1 3.9 4.1 4.0 3.8

0.16 0.10 0.12 0.15 0.20 0.14 0.70 0.44 0.21 0.40

0.04 0.03 0.04 0.02 0.04 0.01 0.05 0.02 0.01 0.02

120 122 127 83 105 110 112 211 210 210

Mekong River basin tributaries and the river main stream 44 Dzachu 3565 8.3 21.9 10.5 45 Dzachu 3285 8.4 40.0 13.5 46 Dzachu 3240 8.5 39.1 12.0 49 Ngomchu – 8.5 39.5 13.0 48 Ngomchu 3240 8.5 40.0 12.2 47 Mekong R. 3240 8.5 39.7 12.5 50 Mekong R. 3240 8.5 42.6 14.5 51 Mekong R. 3168 8.5 42.5 13.6 12 Mekong R. 2195 8.4 36.6 18.3 11 Mekong R. 1912 8.4 36.2 18.6 9 Mekong R. 1841 8.5 35.4 18.5 8 Mekong R. 1841 8.4 34.8 18.9 7 Mekong R. 1779 8.4 34.4 19.4 6 Mekong R. 1702 8.4 32.9 12.1

660 611 479 > 1000 > 1000 > 1000 872 912 571 761 992 > 1000 > 1000 > 1000

33.7 53.7 56.8 52.1 51.5 51.7 53.5 55.6 49.8 47.6 47.4 46.2 46.0 43.8

8.0 13.5 14.4 16.1 16.4 15.8 15.4 15.1 13.4 13.4 12.9 12.3 12.1 11.8

3.1 15.7 17.5 7.3 8.0 7.4 13.2 13.4 13.5 13.0 13.1 12.4 12.1 11.7

0.9 1.5 1.6 1.5 1.6 1.9 1.4 1.4 1.5 1.4 1.6 1.8 1.3 1.3

19.6 66.6 93.7 76.8 76.6 73.6 73.4 77.3 72.8 72.2 69.0 66.9 64.5 62.1

0.42 0.60 0.98 0.36 0.65 0.57 0.55 0.98 <0.02 0.60 0.66 0.56 0.58 0.52

4.5 18.9 22.0 9.1 9.7 8.9 15.6 16.1 16.7 16.0 16.1 15.8 16.4 14.6

119.5 157.3 136.1 147.6 147.9 150.0 157.1 155.6 135.4 129.2 129.7 125.4 124.0 121.0

4.6 4.0 4.8 4.4 4.9 4.5 4.7 5.1 4.2 4.0 4.4 3.9 4.5 4.1

0.42 0.44 0.30 0.34 0.36 1.54 0.34 0.36 0.35 0.30 0.36 0.32 0.34 0.34

0.02 0.03 0.03 0.05 0.03 0.02 0.03 0.05 0.01 0.02 0.05 0.02 0.04 0.01

194 332 348 315 317 314 335 340 307 297 295 285 281 271

Yangtze River basin tributaries and the river main stream 31 Kamtok 3120 8.4 17.0 13.4 32 Kamtok 3120 8.5 16.9 13.4 37 Jomda 3570 8.5 19.1 12.1 36 Jomda 3146 8.5 19.6 12.2 20 Yalong – 8.6 27.4 16.0 19 Yalong 2993 8.6 26.5 16.5 18 Yalong 2861 8.6 25.3 15.7 16 Batangchu 2537 8.2 12.5 12.7 15 Batangchu 2537 8.3 13.0 12.7

419 432 > 1000 > 1000 536 53.1 61.9 6.79 10.4

35.2 33.8 33.4 34.1 36.5 35.1 33.6 20.1 20.9

3.2 3.1 4.5 4.5 13.1 13.4 12.0 2.5 2.7

1.8 1.6 2.8 2.8 5.5 5.6 5.3 2.9 3.1

0.9 0.9 1.1 1.1 0.9 1.1 0.9 0.5 0.6

12.1 12.0 8.7 8.7 23.8 22.8 21.5 21.3 21.5

0.41 0.64 0.41 0.19 0.10 0.10 0.19 0.62 0.58

4.8 5.9 5.0 4.9 5.4 5.2 5.2 6.0 4.4

105.1 98.4 113.2 115.7 153.2 152.6 141.8 44.6 50.8

4.8 6.3 5.9 5.8 4.5 4.9 4.9 5.4 5.4

0.23 0.45 0.43 0.37 0.28 0.31 0.26 0.17 0.12

0.12 0.06 0.08 0.08 0.04 0.05 0.10 0.06 0.10

168 163 175 178 243 241 226 104 110

(continued page) (continued on on next next page)

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Table (continued) A1 (continued) EC

Temp.

Turb.

Ca2+

Mg2+

Na+

K+

SO2− 4

NO− 3

Cl−

HCO− 3

SiO2

TDN

TDP

TDS

mS/m

°C

NTU

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

mg/L

Yangtze River basin tributaries and the river main stream 17 Litangchu 3996 8.5 15.1 12.7 26 Yangtze R. 3258 8.5 71.4 13.7 27 Yangtze R. – 8.5 70.7 14.0 33 Yangtze R. 3097 8.5 68.8 13.8 29 Yangtze R. 3097 8.5 70.2 13.6 28 Yangtze R. 3095 8.5 69.0 13.5 25 Yangtze R. 2970 8.4 78.9 15.7 24 Yangtze R. 2968 8.4 71.6 15.8 23 Yangtze R. – 8.4 68.8 16.0 14 Yangtze R. 2482 8.5 55.7 16.9 13 Yangtze R. 2196 8.5 61.8 17.5 5 Yangtze R. 1895 8.5 46.7 18.4 3 Yangtze R. 1863 8.4 43.4 18.0 2 Yangtze R. 1857 8.4 41.7 19.0 1 Yangtze R. 1827 8.5 40.4 23.1

16.2 > 1000 > 1000 > 1000 > 1000 > 1000 > 1000 934 849 > 1000 > 1000 > 1000 > 1000 681 831

21.5 53.4 52.1 53.1 53.7 51.9 53.4 50.3 51.3 45.0 45.9 40.1 37.6 37.4 37.0

4.3 18.9 19.1 18.7 18.4 18.3 19.7 19.2 18.5 15.4 16.9 12.4 11.8 10.5 10.5

3.8 74.8 72.1 73.8 72.2 70.4 87.3 76.9 74.9 54.6 63.7 45.7 39.6 36.8 34.9

0.7 3.3 3.2 3.2 3.2 3.4 3.4 3.1 3.2 2.7 2.9 2.1 2.1 2.5 1.8

14.7 94.6 95.0 93.5 93.7 92.8 103.2 94.6 91.8 74.0 82.7 54.1 50.9 46.2 44.0

0.63 0.92 0.97 1.15 0.87 0.87 1.12 1.00 1.01 0.55 1.03 0.44 0.46 0.55 0.51

4.2 125.5 126.2 124.8 125.3 124.2 156.1 133.4 130.4 88.4 108.1 75.1 64.4 58.9 55.5

71.5 124.0 112.3 121.6 117.0 109.5 97.8 107.4 110.6 116.8 105.9 110.1 106.4 107.4 108.9

<0.1 5.0 5.0 5.3 5.1 4.5 4.8 5.0 5.3 4.7 5.1 4.6 4.8 4.9 4.9

0.19 0.42 0.42 0.42 0.44 0.38 0.47 0.28 0.47 0.35 0.38 0.29 0.26 0.52 0.36

0.02 0.05 0.05 0.03 0.04 0.04 0.05 0.12 0.05 0.09 0.03 0.01 0.04 0.02 0.04

121 500 486 495 489 476 527 491 487 402 432 344 318 305 298

Yarlung Tsangpo basin 85 Lhasa R. 84 Lhasa R. 96 Lhasa R. 95 Lhasa R. 79 Kyemtangchu 81 Kyemtangchu 73 Nyangchu 70 Nyangchu 69 Nyangchu 68 Nyangchu 63 Rawok Tso 64 Parlung Ts. 66 Parlung Ts. 65 Parlung Ts. 97 Yarlung Ts. 74 Yarlung Ts. 75 Yarlung Ts. 76 Yarlung Ts. 77 Yarlung Ts. 83 Yarlung Ts. 78 Yarlung Ts. 80 Yarlung Ts. 72 Yarlung Ts. 71 Yarlung Ts.

75.7 84.5 94.7 88.8 39.2 37.7 57.4 50.9 48.3 39.2 103 127 104 532 514 > 1000 > 1000 > 1000 > 1000 773 865 828 927 > 1000

22.5 23.1 23.4 21.9 29.7 28.9 12.0 10.2 11.2 10.2 13.1 13.8 17.8 16.9 30.5 26.1 26.2 25.4 25.6 25.8 25.4 26.3 20.4 21.5

4.1 4.0 4.4 3.6 7.4 7.6 2.0 1.8 1.8 1.7 2.0 2.5 2.8 2.6 5.0 4.1 4.1 4.0 4.1 4.2 4.1 4.1 2.9 3.3

2.5 2.7 2.8 3.4 1.7 1.7 1.2 1.1 1.2 1.6 0.9 0.9 0.9 0.8 5.5 3.9 3.8 3.8 3.7 3.8 3.8 3.7 2.7 3.2

0.6 0.7 0.7 0.8 0.3 0.3 0.6 0.6 0.6 0.7 0.4 0.4 0.9 0.9 1.0 0.9 0.8 0.8 0.8 0.8 0.8 0.8 0.7 0.8

27.2 28.4 27.9 23.9 39.0 82.3 16.9 16.1 16.0 16.2 10.4 12.3 16.3 16.0 45.9 25.3 37.9 32.3 25.2 31.1 31.8 38.1 24.2 19.0

0.53 0.49 0.22 0.27 0.57 <0.02 0.50 0.45 0.55 0.42 0.59 0.65 0.67 0.66 0.16 0.16 0.54 0.21 0.06 0.14 0.04 0.11 0.02 0.28

4.7 4.9 5.0 5.5 4.4 4.2 0.5 4.4 4.3 4.7 4.2 4.2 4.1 4.2 6.3 5.2 5.4 5.3 5.0 5.1 5.4 5.6 5.1 5.9

53.6 53.9 57.7 54.9 75.0 19.3 27.8 15.6 18.8 15.9 32.2 34.2 43.6 40.1 64.8 70.7 53.7 58.1 68.7 62.3 59.4 53.3 45.3 56.9

4.4 4.4 5.2 5.9 4.0 4.1 3.2 3.0 3.5 3.2 3.0 1.9 2.6 2.6 5.9 5.3 5.4 5.8 5.2 5.4 5.9 5.6 4.6 4.2

0.26 0.30 0.30 0.33 0.14 0.32 0.10 0.13 0.07 0.30 0.04 0.12 0.07 0.13 1.01 0.21 0.35 0.25 0.26 0.30 0.21 0.51 0.19 0.24

0.04 0.03 0.02 0.02 0.03 0.02 0.01 0.04 0.06 0.04 0.03 0.01 0.02 0.04 0.04 0.04 0.06 0.10 0.06 0.01 0.05 0.05 0.02 0.03

120 123 127 120 162 148 65 53 58 55 67 71 90 85 165 142 138 136 138 139 137 138 106 115

St.

River

No.

Elevation

pH

m

tributaries and the river main 3767 8.2 16.2 3719 8.1 17.0 3650 8.2 16.4 3612 8.2 15.4 3079 7.7 23.5 3049 7.7 22.9 3081 8.0 6.9 3014 7.9 7.7 3009 7.9 7.8 2989 7.8 8.1 3743 8.5 8.7 – 8.3 9.3 2686 8.5 11.6 2635 8.4 11.2 3596 8.5 21.4 3193 8.4 18.7 3154 8.4 18.7 3136 8.3 18.4 3127 8.3 18.4 3115 8.3 18.4 3053 8.3 18.5 – 8.1 18.3 2934 8.5 13.8 2927 8.5 15.3

stream 12.5 11.6 14.9 14.7 10.0 10.6 11.7 11.4 11.4 11.5 12.1 10.5 9.1 9.7 16.5 17.1 17.1 17.1 17.1 17.6 16.4 16.5 14.7 15.0

Table A2 Some of the measured element concentrations in the Salween River, Mekong River, Yangtze River, Yarlung Tsangpo and their tributaries in the Tibetan Plateau. St.

River

Al

Fe

Li

Mn

Mo

Ti

Zn

S

µg/L

µg/L

µg/L

µg/L

µg/L

µg/L

µg/L

mg/L

Salween River basin tributaries and the river main stream 52 Yuchu 5.3 53 Yuchu 7.4 54 Yuchu 8.0 62 Lengchu 31.4 61 Lengchu 14.7 58 Lengchu 27.5 60 Lengchu 22.8 57 Salween R. 30.9 56 Salween R. 26.7 55 Salween R. 18.6

28.9 23.8 21.7 43.3 11.7 18.8 12.6 20.6 11.1 2.2

4.7 5.2 3.7 10.2 14.1 9.9 12.7 12.0 11.1 10.0

4.2 3.5 6.2 2.5 3.7 3.9 3.6 4.5 4.4 0.6

1.3 0.7 1.1 1.5 1.9 1.7 2.0 0.7 <0.6 0.8

0.6 0.6 0.7 2.8 1.0 1.4 1.0 0.8 0.7 0.5

5.0 6.6 6.3 4.3 6.2 7.8 5.4 4.2 2.7 1.8

6.0 5.9 5.9 3.7 6.3 7.8 8.5 18.3 18.4 18.2

Mekong River basin tributaries and the river main stream 44 Dzachu 45 Dzachu 46 Dzachu 49 Ngomchu 48 Ngomchu 47 Mekong R. 50 Mekong R. 51 Mekong R. 12 Mekong R.

5.1 10.5 0.6 <3.4 1.9 11.5 1.5 1.0 <3.4

6.5 15.5 17.8 21.2 17.4 20.8 18.5 15.8 17.7

4.3 3.6 1.4 5.0 4.8 5.8 2.0 2.0 0.4

1.0 1.3 1.0 0.9 1.2 0.7 1.2 1.2 1.3

0.6 0.6 0.5 0.4 0.5 0.6 0.5 0.6 0.5

2.7 4.9 5.3 5.4 4.3 3.6 3.1 4.3 3.6

5.7 23.2 25.5 26.6 26.6 26.8 26.0 26.1 24.3

No.

23.6 14.7 9.7 8.7 8.5 15.5 9.1 9.7 13.6

X. Huang et al. / Science of the Total Environment 407 (2009) 6242–6254

6253

Table (continued) A2 (continued) St.

River

Al

Fe

Li

Mn

Mo

Ti

Zn

S

µg/L

µg/L

µg/L

µg/L

µg/L

µg/L

µg/L

mg/L

Mekong River basin tributaries and the river main stream 11 Mekong R. 14.8 9 Mekong R. 18.9 8 Mekong R. 21.2 7 Mekong R. 20.1 6 Mekong R. 22.4

0.5 3.8 3.7 0.7 3.2

20.8 16.3 18.3 15.5 15.8

0.4 0.8 1.2 0.4 0.6

1.3 1.1 1.3 1.1 1.3

0.6 0.7 0.5 0.5 0.6

5.5 7.2 3.1 2.9 5.0

23.7 23.1 22.5 21.7 20.7

Yangtze River basin tributaries and the river main stream 31 Kamtok 32 Kamtok 37 Jomda 36 Jomda 20 Yalong 19 Yalong 18 Yalong 16 Batangchu 15 Batangchu 17 Litangchu 26 Yangtze R. 27 Yangtze R. 33 Yangtze R. 29 Yangtze R. 28 Yangtze R. 25 Yangtze R. 24 Yangtze R. 23 Yangtze R. 14 Yangtze R. 13 Yangtze R. 5 Yangtze R. 3 Yangtze R. 2 Yangtze R. 1 Yangtze R.

10.1 10.3 26.1 36.6 10.9 7.4 7.5 6.3 6.3 13.3 14.6 13.7 9.5 31.8 9.1 12.2 10.8 13.7 12.8 13.8 18.3 23.0 21.4 22.7

4.6 3.0 19.0 34.4 3.4 3.3 3.6 4.3 3.8 31.2 8.7 4.2 2.6 37.7 <3.4 <3.4 <3.4 3.8 1.7 2.3 2.4 2.6 <3.4 <3.4

2.8 2.2 4.7 6.3 10.7 10.9 10.6 11.0 12.2 14.6 70.6 68.5 66.7 67.7 70.0 73.7 69.0 66.4 56.6 65.8 39.5 37.8 36.0 36.4

2.9 3.0 11.1 15.2 0.5 1.0 0.6 1.3 1.0 4.2 2.3 1.7 0.6 6.2 0.6 1.1 0.8 0.8 0.3 0.3 0.5 0.9 2.7 1.7

<0.6 0.8 1.0 1.0 0.6 1.1 0.7 0.8 1.5 1.1 0.8 1.7 1.0 1.5 1.3 1.2 1.1 1.0 1.6 1.2 1.3 1.4 1.2 1.2

0.5 0.7 0.6 0.7 0.7 0.6 0.7 0.7 0.6 0.7 0.7 0.5 0.5 1.0 0.4 0.5 0.5 0.6 0.5 0.6 0.5 0.6 0.6 0.6

3.0 3.5 3.3 3.7 6.1 5.1 3.5 10.8 7.8 3.0 4.6 3.3 4.9 2.0 5.0 3.8 7.4 3.0 2.1 2.4 4.2 3.6 10.1 3.9

<3.4 <3.4 <3.4 <3.4 6.9 6.6 6.4 6.2 6.3 3.9 31.8 31.0 31.5 30.8 29.9 33.6 30.5 30.3 24.7 27.0 18.3 16.8 15.6 15.0

Yarlung Tsangpo basin tributaries and the river main stream 85 Lhasa R. 31.2 84 Lhasa R. 80.1 96 Lhasa R. 32.8 95 Lhasa R. 30.9 79 Kyemtangchu 44.4 81 Kyemtangchu 42.1 73 Nyangchu 21.9 70 Nyangchu 25.3 69 Nyangchu 23.2 68 Nyangchu 20.9 63 Rawok Tso 24.7 64 Parlung Ts. 39.8 66 Parlung Ts. 56.5 65 Parlung Ts. 36.6 97 Yarlung Ts. 18.3 74 Yarlung Ts. 18.6 75 Yarlung Ts. 18.3 76 Yarlung Ts. 16.3 77 Yarlung Ts. 17.2 83 Yarlung Ts. 17.3 78 Yarlung Ts. 15.5 80 Yarlung Ts. 19.7 72 Yarlung Ts. 31.3 71 Yarlung Ts. 24.5 WHO (2004) n SEPA & AQSIQ (2002) – MOH & SAC (2006) 200

26.6 20.8 27.5 34.7 4.4 5.7 10.2 16.6 12.7 18.4 11.9 35.4 61.0 19.6 3.2 4.8 6.6 4.2 3.1 5.9 6.3 6.9 7.8 3.9 n 300 300

15.9 14.3 16.0 27.3 7.7 11.2 3.3 3.8 6.8 5.9 6.6 7.3 3.6 2.5 29.9 22.0 20.7 22.0 19.6 22.0 21.6 20.6 14.7 18.6 – – –

7.8 17.9 7.3 9.8 152.3 153.7 5.7 5.4 5.3 16.3 1.0 3.1 5.9 4.7 1.6 0.6 0.7 0.6 0.5 0.6 0.5 0.6 1.3 0.7 400 100 100

1.9 <0,6 1.2 1.7 <0.6 0.8 1.2 1.2 1.6 0.9 1.5 1.0 2.0 1.7 1.8 1.7 1.7 1.7 1.4 1.9 1.9 1.4 1.4 1.8 70 70 70

0.9 0.7 1.0 1.2 0.5 0.6 0.7 0.9 1.0 0.8 0.8 1.3 3.1 1.7 0.7 0.7 0.8 0.6 0.8 0.8 0.7 0.8 0.7 0.7 – 100 –

6.8 6.1 3.8 5.7 11.2 10.1 4.0 5.3 20.5 5.6 4.4 4.5 4.5 2.6 3.0 3.4 3.4 3.1 4.4 2.0 2.2 4.2 3.2 4.6 n 50 1000

8.3 8.3 8.2 7.0 27.8 27.4 4.8 4.4 4.4 4.1 <3.4 <3.4 4.7 4.6 13.9 10.6 9.9 9.7 10.0 9.9 10.0 10.0 7.0 7.9 – 50 20

No.

n: no health-based guideline value is proposed. Hyphen indicates no information available.

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