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Journal of Geographical Sciences >

2015 , Vol. 25 >Issue 6: 669 - 686

DOI: https://doi.org/10.1007/s11442-015-1195-6

Orginal Article

Hydrochemical characteristics and element contents of natural waters in Tibet, China

  • TIAN Yuan , 1, 2 ,
  • YU Chengqun , 1, * ,
  • LUO Kunli , 1, * ,
  • ZHA Xinjie 3 ,
  • WU Jianshuang 1 ,
  • ZHANG Xianzhou 1 ,
  • NI Runxiang 1, 2
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  • 1. Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China
  • 2. University of Chinese Academy of Sciences, Beijing 100049, China
  • 3. Xi’an University of Science and Technology, Xi’an 710054, China

*Corresponding author: Yu Chengqun, Professor, E-mail:; Luo Kunli, Professor, E-mail:

Author: Tian Yuan (1991-), Graduate student in Institute of Geographic Sciences and Natural Resources Research, CAS, specialized in geology and health, environmental science. E-mail:

Received date: 2014-10-20

  Accepted date: 2014-11-16

  Online published: 2015-06-15

Supported by

National Key Technologies R&D Program in the 12th Five-Year Plan of China, No.2011BAD17B05-4, No.2011BAC09B03

National Key Basic Research Program of China (973 Program), No.2014CB238906

National Natural Science Foundation of China, No.40872210, No.41172310, No.40171006

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Journal of Geographical Sciences, All Rights Reserved
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Abstract

Sixty water samples (35 groundwater samples, 22 surface water samples and three hot-spring water samples) were collected at 36 points from villages and towns in Lhasa city, Nagchu (Nagqu) prefecture, Ali (Ngari) prefecture and Shigatse (Xigaze) prefecture (Tibet) in 2013 to study the hydrochemical characteristics and element contents of natural waters. The concentrations of elements were determined in the water samples and compared with the concentrations in water samples from other regions, such as southeast Qinghai, south Xinjiang, east Sichuan and west Tibet. The hydrochemical species in different areas were also studied. Water in most parts of Tibet reaches the requirements of the Chinese national standard and the World Health Organization international standard. The pH values of the water samples ranged from 6.75 to 8.21 and the value for the mean total dissolved solids was 225.54 mg/L. The concentration of arsenic in water from Ali prefecture exceeded the limit of both the Chinese national standard and the international standard and the concentration of fluoride in water from Shuanghu exceeded the limit of both the Chinese national standard and the international standard. The main hydrochemical species in water of Tibet is Ca (HCO3)2. From south to north, the main cation in water changes from Ca2+ to Na+, whereas the main anions in water change from HCO3- to Cl- and SO42-. The chemistry of river water and melt water from ice and snow is dominated by the rocks present at their source, whereas the chemistry of groundwater is affected by many factors. Tectonic divisions determine the concentrations of the main elements in water and also affect the hydrochemical species present.

Key words： element concentrations; hydrochemical species; water chemistry; water quality; Tibet

Cite this article

TIAN Yuan , YU Chengqun , LUO Kunli , ZHA Xinjie , WU Jianshuang , ZHANG Xianzhou , NI Runxiang . Hydrochemical characteristics and element contents of natural waters in Tibet, China[J]. Journal of Geographical Sciences, 2015 , 25(6) : 669 -686 . DOI: 10.1007/s11442-015-1195-6

1 Introduction

The Tibet Autonomous Region (26°44'-36°32'N, 78°25'-99°06'E) is located on the Qinghai-Tibet Plateau on the southwestern border of China. It has a land area of 1.22 × 106 km2 with an average elevation being >4 km above sea level. The geology of Tibet is complicated and diverse and there are unique geological hazards in this region (Shen et al., 2011).
According to China’s Water Resource Report in 2007 (MWR, 2009), the inflowing rivers and lake water in Tibet have enormous capacity, low elements concentrations and are of good quality; the waters are mainly composed of rain, ice/snow melt water and groundwater. The average volume of surface water resources in Tibet is 4.394×1011 m3 per year, which accounts for 17% of the total surface water resources of China’s mainland. The total volume of groundwater resources in Tibet is about 9.661×1010 m3. The cover area and volume of the glaciers in Tibet account for 48.2% of the surface cover and 53.6% of the total volume of the glaciers in China (MWR, 2009; Bian et al., 2010). The volume of ice/snow melt water in Tibet is about 3 × 1011 m3.
Zhang et al. (2013) analyzed the quality of drinking water in Nyingchi, Tibet in 2011, which showed that the water quality in Nyingchi did not often reach the required standard for drinking water. Liu and Ge (2012) determined trace elements in lake water from a mining area using the inductively coupled plasma mass spectrometry (ICP-MS) and compared the results with those obtained by four other methods to determine the optimum sample recovery rate. Bu et al. (2011) determined the concentration of arsenic in three fish ponds in Lhasa. The arsenic concentration in Quxu Niedang fish pond was the highest at >60 μg/L. Nie et al. (2011) analyzed the microbiological indicators in drinking water from counties in Lhasa and found that the water quality did not often reach the required microbiological standards for drinking water. Wang et al. (2013) studied the hydrochemical characteristics of Lake Manasarovar and Lake Rakshastal and showed that the pH was inversely proportional to the amount of dissolved oxygen. Zheng et al. (2007a, 2007b, 2008) monitored and tested the water quality in some areas of Naqu and Biru where troops were stationed; the water samples did not often reach the required standard for drinking water and the arsenic concentration commonly exceeded the Chinese national standard. Zhang et al. (2009) and Li et al. (2010) analyzed the hydrochemical characteristics of water samples collected from the Niyang and Yarlung Zangbo rivers in Tibet and reported some basic data for the water samples. Liu et al. (2013) analyzed the results of a drinking water safety project in rural areas of Shannan in 2012; the results showed that some water samples were polluted. Luo et al. (2010) surveyed the water quality of about 140 urban drinking water sources in Tibet and found that 96.9% of the drinking water samples in urban areas met the required standard for drinking water. Zhao et al. (2002) investigated the water quality of self-supplied water sources in some remote areas where troops were stationed and water sanitation was poor.
There have been few systematic studies of the geochemical features and element concentrations of waters in Tibet. We investigated the elemental composition and distribution of water in Tibet in August 2013 (Figure 1) and collected water samples for analysis. From September to October, we determined the elemental composition and hydrochemical characteristics of water samples at the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences (IGSNRR, CAS). We also studied the hydrochemical and element characteristics of these water samples. This paper is a comprehensive report of the concentration and distribution of elements in waters from different geological areas of Tibet.
Figure 1 Geographical location, tectonic divisions (based on Ma et al., 2002) and distribution of water sampling points in Tibet

2 Study areas and methods

2.1 Sampling sites and types of samples

Sixty water samples (35 groundwater samples, 22 surface water samples and three hot-spring samples) were collected (Tables 1 and 2) from the majority of counties in Lhasa city, Nagchu prefecture, Ali prefecture and Shigatse prefecture in Tibet. The tap water for everyday use in Tibet comes from untreated shallow wells, river water and ice/snow melt water. These samples (nine samples from the Himalayan partition, 38 samples from Gangdise-Nyenchen Tanglha partition and 13 samples from the South and Central Changtang-Zuogong partition) therefore reflected the range of hydrochemical characteristics and types of natural water in Tibet.
Table 1 Distribution of surface water sampling locations in Tibet
Sample No. Date Latitude
(°)		 Longitude
(°)		 Elevation (m) Sample site Sample type
1 2013.04.27 29.566389 91.401144 4196 No.7 team, Xincang village, Dazi county River water
2 2013.04.27 29.570000 91.393056 4287 No.7 team, Xincang village, Dazi county Ice/snow melt
5 2013.07.13 29.604167 91.380833 3970 No.6 team, Xincang village, Dazi county River water
6 2013.07.20 29.873056 91.093333 3972 Bailang village, Linzhou county River water
7 2013.07.20 29.873056 91.093333 3972 Bailang village, Linzhou county River water
8 2013.07.20 29.871667 91.092500 3954 Bailang village, Linzhou county River water
9 2013.07.20 29.850000 91.092222 4041 Bailang village, Linzhou county River water
12 2013.07.24 30.495000 91.069167 4317 Dangxiong field station Ice/snow melt
14 2013.08.04 32.105833 92.285278 4645 Nyainrong, Nyainrong county River water
15 2013.08.04 32.109722 92.302500 4634 Nyainrong, Nyainrong county Ice/snow melt
21 2013.08.05 31.273333 92.102778 4450 Kema village, Luoma town, Nagchu River water
26 2013.08.08 32.301111 91.868056 4683 Amdo county River water
27 2013.08.08 32.303333 91.906944 4732 Shenkagang village, Amdo county River water
35 2013.08.11 32.433056 89.081111 4791 Duoma township, Shuanghu county River water
36 2013.08.11 33.206944 88.798611 4981 Shuanghu county Ice/snow melt
38 2013.08.12 32.286944 87.901944 4754 Cuozheluoma town, Shuanghu county River water
44 2013.08.17 31.370000 85.091667 4728 Gerze county River water
52 2013.08.21 31.451111 80.120556 4675 Alzadar county River water
53 2013.08.21 30.970278 81.285000 4679 Baga town, Burang county Ice/snow melt
54 2013.08.22 30.776389 81.613611 4625 Huoer town, Burang county Ice/snow melt
57 2013.08.22 29.088611 87.637778 4048 Lhatse county River water
58 2013.18.23 29.278889 88.879167 3777 Shigatse River water
Table 2 Distribution of groundwater sampling locations in Tibet
Sample number Date Latitude (°) Longitude (°) Elevation (m) Sample site Depth (m)
3 2013.04.28 29.642406 91.180731 3666 Tibet University, Lhasa -
4 2013.04.28 29.642950 91.180108 3666 Tibet University, Lhasa 6
10 2013.07.23 30.476389 91.099722 4297 Damxung county 5
11 2013.07.23 30.477500 91.103056 4281 Damxung county 30
13 2013.08.03 31.475908 92.062089 4521 Nagchu town, Nagqu county -
16 2013.08.04 32.110000 92.303611 4612 Nyainrong 10
17 2013.08.04 31.465556 92.062778 4508 Nagchu town, Nagchu 10
18 2013.08.05 31.468611 92.059167 4534 Nagchu town, Nagchu -
19 2013.08.05 31.271944 92.158611 4471 Kema village, Luoma town, Nagqu county 10
20 2013.08.05 31.271944 92.160000 4439 Kema village, Luoma town, Nagqu county 5
22 2013.08.05 31.469167 92.047500 4523 Nagchu town, Nagqu county 27
23 2013.08.05 31.275833 92.105278 4459 Nagqu field station, Nagqu county 10
24 2013.08.06 31.471944 92.047500 4506 Nagqu Agriculture Bureau, Nagqu county -
25 2013.08.07 32.264050 91.681160 4685 Amdo county -
28 2013.08.09 31.405278 90.835278 4606 Baila town, Baingoin county 6
29 2013.08.09 31.395000 90.007778 4703 Baingoin county 15
30 2013.08.10 31.523333 89.741111 4576 Mendang town, Baingoin county 4
31 2013.08.10 32.390000 89.218889 4703 Duoma town, Shuanghu county (40ºC) -
32 2013.08.10 32.386667 89.149167 4701 Duoma township, Shuanghu county (50ºC) -
33 2013.08.10 32.388056 89.149722 4708 Duoma township, Shuanghu county (60ºC) -
34 2013.08.10 32.384444 89.145278 4705 Duoma town, Shuanghu county 15
37 2013.08.12 33.233056 88.352222 4811 Jiacuo, Shuanghu county 4
39 2013.08.13 31.786111 87.234722 4553 Nyima county -
40 2013.08.15 31.876944 86.061667 4797 Asuo town, Nyima county 6
41 2013.08.15 31.253056 86.014722 4726 Juncang town, Nyima county 8
42 2013.08.16 31.263333 85.563056 4690 Cishi town, Cuoqin county 10
43 2013.08.16 31.018056 85.153889 4649 Cuoqin county 10
45 2013.08.17 32.098611 84.878889 4433 Dongco, Gerze county -
46 2013.08.17 32.300000 84.055278 4447 Gerze county 11
47 2013.08.18 32.040697 83.669022 4398 Marm, Gerze county 5
48 2013.08.19 32.371667 82.891111 4474 Wenbudangsang town, Geji county -
49 2013.08.19 32.388333 81.143333 4542 Geji county 5
50 2013.08.20 32.503333 80.090000 4308 Seng-ge Kambab -
51 2013.08.21 31.481389 79.801111 3755 Tholing, Zanda county 35
55 2013.08.22 29.652169 84.181464 4602 Laozhongba town, Zhongba county 6
56 2013.08.22 29.419006 86.724014 4632 Sangsang town, Ngamring county 10
59 2013.18.23 29.346667 89.635833 3752 Dazhu village, Shigatse 15
60 2013.08.24 29.676389 91.344722 3699 Dazi county Lhasa field station 30

2.2 Sampling and analysis

2.2.1 Sampling and preservation
The authors strictly complied with the methods in Monitoring and Analysis Methods for Water and Waste Water (MEP, 2002) to collect water samples from different geological areas in Tibet in August 2013. The sample containers used were colorless 0.5 L polythene plastic barrels and were dipped into nitric acid for 24 h before use. The containers were then washed sequentially with 10% hydrochloric acid solution and tap water. The containers were then washed with distilled water and finally flushed three times with sampling water.
2.2.2 Methods of analysis
The water samples were analyzed at the IGSNRR, CAS. The pH, Ec, RES, salinity (SAL), total dissolved solids (TDS) and temperature were determined using a Switzerland Mettler Toledo pH tester (SevenGo SG2) and Switzerland Mettler Toledo Ec tester (SevenGo SG3). The Eh was determined in situ using a Shanghai Sanxin ORP tester (SX712). The total hardness (TH) was calculated from the concentrations of Ca2+ and Mg2+. The alkalinity (as HCO3-) was determined by acid-base titration (MH, 1985; MEP, 2002). The chloride (Cl-) concentration of the water samples was determined using a chloride ion-selective electrode (Hirokazu et al., 1985; Yu et al., 2010) and the fluoride (F-) concentration was determined using a fluoride ion-selective electrode (MH, 1985; MEP, 2002). All water samples were stored in pre-cleaned plastic bottles at 4°C before analysis. Selenium and arsenic were determined by hydride generation atomic fluorescence spectrometry (MH, 1985; MEP, 2002). The concentrations of the major cations (Ca2+, Mg2+, Na+, K+, P, Sr, B and SiO2) and the SO42- anion were determined by inductively coupled plasma atomic emission spectrometry (Optima 5300 DV, Waltham, Massachusetts in the United States, PerkinElmer). The concentrations of trace elements (Li, Zn, U, Rb, Ba, Bi, Co, Cs, Ga, In, Ti, V, Ag, Al, Be, Cd, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb and Tl) were determined by ICP-MS (PerkinElmer, DRC-e). In each test method, a parallel sample was determined to ensure the stability of the data after every 20 samples. The percentage error in all the samples ranged from ±0.19% to ±4.96%, i.e. less than ±5% (Figure 2). Therefore these data are accurate and dependable (Shen et al., 1993; Ji et al., 2007).
Figure 2 Total cations versus total anions in water samples from Tibet

3 Results

3.1 Hydrochemical characteristics and element concentrations

The water samples collected from Tibet have good hydrochemical and sensory characteristics (Tables 3 and 4). The pH in these samples ranged from 6.75 to 8.21, with a mean value of 7.54. The average TDS was about 225.54 mg/L, except for the hot-spring water. Because the majority of the water samples were collected from surface runoff, which is mainly recharged by ice/snow melt, the hardness of these samples ranged from soft to moderately hard.

3.2 Trace element concentrations

The background concentrations of elements from different geological settings not only affect the hydrochemical characteristics of the major elements in water, but also affect the hydrochemical characteristics of the trace elements (Warren, 1989; Webster, 1994). The average selenium concentration of the water samples was 0.154 μg/L (maximum 0.898 μg/L). The average fluoride concentration was 0.44 mg/L (maximum 7.24 mg/L). However, the average fluoride concentration of the hot-spring water samples was 4.62 mg/L, higher than that of the other samples. The fluoride concentration in Shuanghu county was also high, with an average concentration of about 2.31 mg/L (Tables 5 and 6).
Table 3 Hydrochemical characteristics and element concentrations in surface water samples from Tibet
Sample number pH Eh
(mV)		 Ec
(μs/cm)		 TDS
(mg/L)		 TH
(mg/L)		 Ca2+
(mg/L)		 Mg2+
(mg/L)		 Na+
(mg/L)		 K+
(mg/L)		 HCO3
(mg/L)		 SO42-
(mg/L)		 Cl-
(mg/L)		 SiO2
(mg/L)
1 7.62 336 179 90 84 28.9 2.8 2.2 0.7 39.7 32.6 11.0 6.8
2 7.30 293 197 99 105 40.2 1.2 1.9 0.3 91.5 10.6 6.1 10.2
5 7.36 220 151 76 77 26.6 2.6 2.4 0.4 54.9 3.2 12.8 12.6
6 7.45 224 96 48 44 13.6 2.4 2.7 0.7 15.3 12.0 8.7 6.5
7 7.38 217 80 40 37 11.3 2.0 1.4 0.5 9.2 11.5 9.0 5.7
8 7.29 235 95 47 44 13.6 2.4 2.8 0.7 21.4 12.2 10.1 6.6
9 7.31 227 76 38 36 11.2 1.9 1.4 0.5 10.7 11.9 6.6 5.8
12 7.15 226 133 66 68 21.5 3.5 1.3 0.8 39.7 21.5 8.8 4.5
14 7.77 202 263 131 133 38.3 9.0 9.7 1.5 122.0 7.8 7.2 9.1
15 7.55 209 348 174 186 53.0 12.8 9.7 1.2 155.6 12.6 34.3 10.4
21 7.37 213 187 93 78 20.8 6.3 13.9 1.6 73.2 12.3 10.0 8.8
26 7.65 185 529 265 268 67.1 24.1 27.1 3.0 268.5 59.8 14.4 7.6
27 7.81 175 401 200 217 69.8 10.1 14.6 2.0 253.2 8.6 9.6 11.0
35 7.80 185 1530 765 443 73.0 62.5 218.7 3.9 192.2 521.0 98.9 8.7
36 8.02 172 344 172 180 26.3 27.5 11.9 3.7 125.1 32.8 27.5 9.1
38 8.21 168 278 139 158 45.4 10.6 4.7 1.3 94.6 44.3 12.4 8.5
44 7.90 188 368 184 196 58.6 11.8 11.8 1.8 155.6 56.3 13.6 11.8
52 7.72 209 595 298 352 75.8 38.9 9.0 4.3 167.8 158.5 17.5 9.7
53 7.90 200 172 86 89 23.8 7.0 4.4 0.7 18.3 39.3 21.9 4.7
54 7.96 207 90 45 43 12.8 2.6 3.1 0.9 3.1 12.3 20.3 6.2
57 7.64 219 226 113 121 40.3 4.9 4.6 0.8 79.3 30.7 15.4 9.4
58 7.73 225 355 178 194 50.9 15.9 8.9 0.5 128.1 43.6 18.3 18.3
Table 4 Hydrochemical characteristics and element contents in groundwater samples from Tibet
Sample number pH Eh
(mV)		 Ec(μs/
cm)		 TDS
(mg/L)		 TH
(mg/L)		 Ca2+
(mg/L)		 Mg2+
(mg/L)		 Na+
(mg/L)		 K+
(mg/L)		 HCO3-
(mg/L)		 SO42-
(mg/L)		 Cl-
(mg/L)		 SiO2
(mg/L)
3 7.28 262 250 125 119 38.1 5.6 7.0 1.3 91.5 21.3 8.5 12.7
4 7.31 244 261 131 124 38.6 6.5 7.4 1.5 85.4 27.2 9.5 9.6
10 6.95 245 279 139 134 39.9 8.1 10.5 1.5 103.7 10.4 15.8 16.9
11 7.11 233 161 81 83 24.3 5.3 3.2 1.0 64.1 6.4 10.0 11.1
13 7.10 252 1587 793 605 131.4 66.5 152.2 7.8 485.1 156.0 182.1 10.0
16 7.37 213 600 300 320 112.3 9.4 13.7 1.8 280.7 29.6 26.6 10.6
17 7.28 230 1399 699 563 102.4 73.8 112.0 4.0 515.6 143.7 152.8 9.0
18 7.81 205 404 202 165 31.7 20.6 33.7 3.7 155.6 44.1 16.3 6.8
19 7.37 220 467 233 237 69.1 15.4 19.7 3.2 192.2 35.3 18.1 25.5
20 6.93 235 458 229 227 61.9 17.4 18.6 4.1 167.8 46.0 16.2 33.1
22 7.07 243 2480 124 667 151.4 69.2 292.0 13.6 167.1 95.5 860.6 12.6
23 7.34 222 732 366 216 52.2 20.5 103.2 5.0 378.3 44.3 32.0 9.4
24 7.20 220 1055 528 445 134.0 26.4 77.6 5.4 387.5 94.5 89.7 15.4
25 7.37 207 554 277 282 69.2 26.1 23.3 2.9 259.3 49.5 17.2 9.6
28 7.86 191 337 168 169 33.2 20.6 15.8 1.5 198.3 12.0 10.5 10.6
29 7.56 210 804 402 389 126.2 17.5 34.5 3.6 405.8 52.7 15.6 15.4
30 7.79 195 307 154 148 32.6 15.9 16.7 2.5 61.0 19.3 65.0 10.1
31 6.75 245 1999 1000 472 144.4 26.7 363.3 20.8 970.2 86.4 35.3 25.9
32 7.46 226 4360 2180 182 48.7 14.5 1171.0 53.4 2785.6 196.3 57.5 31.5
33 7.19 220 2970 1487 183 57.3 9.5 732.3 33.8 1424.8 137.8 40.1 89.9
34 7.55 180 972 486 315 81.6 26.5 131.5 8.5 585.8 43.0 18.1 22.9
37 7.77 189 693 346 336 79.6 32.8 35.3 7.4 231.9 146.6 40.9 9.3
39 7.89 187 669 334 169 26.1 25.0 98.1 5.6 195.3 64.6 50.7 13.7
40 7.84 193 540 270 224 56.8 19.8 45.2 6.5 286.8 49.5 21.6 11.6
41 7.89 185 340 170 171 59.5 5.3 16.4 1.8 146.4 9.5 39.9 15.2
42 7.64 201 814 407 368 102.5 26.7 43.7 4.8 106.8 154.5 119.7 17.4
43 7.93 193 266 133 134 36.5 10.2 10.0 3.0 109.8 24.8 19.4 16.7
45 7.55 208 793 397 428 100.3 42.6 33.3 4.2 347.8 93.0 37.8 16.6
46 7.73 199 628 314 210 38.1 27.5 71.0 4.0 207.5 76.0 51.4 17.4
47 7.64 223 72 36 315 51.4 44.9 59.8 16.2 205.9 122.1 79.0 36.8
48 7.73 202 433 217 206 44.3 23.0 24.4 3.5 183.1 49.8 25.1 12.0
49 7.81 199 270 135 107 35.7 4.3 21.0 2.7 85.4 29.9 21.6 17.3
50 7.62 208 578 289 243 66.2 18.6 42.6 3.9 231.9 48.8 44.0 17.2
51 7.81 202 311 155 163 40.2 15.0 10.2 2.5 97.6 53.0 13.6 13.5
55 7.46 230 770 385 362 124.1 12.4 18.2 2.3 238.0 39.9 86.7 13.7
56 7.55 222 457 229 233 69.8 14.1 12.0 1.2 112.9 36.2 61.9 15.6
59 7.81 223 300 150 178 29.9 24.7 3.3 0.7 137.3 5.5 17.7 21.1
60 7.72 233 211 106 107 35.7 4.4 5.7 1.5 42.7 26.9 27.7 11.9

3.3 Test results of toxic elements

The average arsenic concentration in water samples (except the hot-spring water samples) in Tibet was 8.66 μg/L. The arsenic concentration in northern Tibet (Damxung, Shuanghu, Gerze, Geji and Seng-ge Kambab) was higher than that in other areas of Tibet, with an average value of about 113.23 μg/L, 11 times higher than the Standards for Drinking Water Quality (MH, 2006; 10 μg/L) (Tables 7 and 8). The water in these areas is therefore not suitable for drinking.
Table 5 Concentrations of trace elements in surface water samples from Tibet
Sample number Li
(μg/L)		 Sr
(mg/L)		 B
(mg/L)		 Zn
(μg/L)		 Se
(μg/L)		 F
(mg/L)		 U
(μg/L)		 Rb
(μg/L)		 Ba
(μg/L)		 Co
(μg/L)		 Cs
(μg/L)		 Ga
(μg/L)		 V
(μg/L)
1 0.25 0.10 0.01 1.48 0.00 0.02 0.20 0.36 4.43 0.04 0.00 0.20 0.08
2 0.87 0.09 0.01 0.36 0.20 0.04 0.15 0.05 0.42 0.06 0.01 0.01 -0.11
5 0.16 0.07 0.01 7.77 0.00 0.04 0.24 0.28 1.56 0.03 0.46 0.08 0.77
6 2.29 0.05 0.09 3.48 0.00 0.04 0.03 0.62 3.16 0.06 0.10 0.17 0.11
7 0.33 0.04 0.01 2.16 0.00 0.04 0.02 0.31 1.86 0.04 0.03 0.10 -0.12
8 2.20 0.05 0.10 1.97 0.03 0.04 0.04 0.51 2.65 0.07 0.06 0.13 0.04
9 0.38 0.04 0.01 1.12 0.00 0.04 0.02 0.37 1.92 0.05 0.04 0.11 -0.06
12 0.92 0.06 0.01 1.86 0.00 0.06 0.71 0.77 3.26 0.03 0.03 0.17 -0.06
14 12.6 0.14 0.12 0.57 0.01 0.25 5.57 0.65 11.97 0.07 0.04 0.54 -0.07
15 10.2 0.49 0.09 1.17 0.08 0.36 3.28 1.99 7.77 0.07 0.83 0.38 -0.07
21 8.23 0.09 0.11 3.06 0.02 0.17 0.18 1.42 5.74 0.10 0.17 0.36 0.31
26 42.5 0.37 0.25 0.92 0.07 0.16 1.13 5.10 50.22 0.08 2.22 2.24 -0.30
27 14.4 0.26 0.22 0.55 0.01 0.16 3.37 0.57 25.26 0.10 0.03 1.10 -0.16
35 140 3.05 1.50 2.91 0.52 0.58 10.85 0.42 13.08 0.10 0.18 0.56 0.27
36 18.3 0.30 0.18 57.33 0.25 0.15 0.93 1.84 29.23 0.03 0.69 1.28 0.28
38 8.87 0.25 0.24 1.97 0.11 0.13 1.58 0.50 7.19 0.05 0.10 0.32 -0.23
44 162 0.24 0.52 1.72 0.18 0.18 1.20 6.96 16.13 0.05 18.83 0.69 -0.36
52 22.3 0.69 0.34 4.18 0.85 0.04 1.35 7.76 12.15 0.06 12.05 0.50 -0.43
53 2.48 0.18 0.07 5.80 0.13 0.15 0.31 0.66 13.27 0.09 0.28 0.60 -0.43
54 2.59 0.08 0.14 3.70 0.19 0.07 0.08 0.78 5.95 0.03 0.07 0.24 -0.36
57 2.67 0.12 0.10 2.46 0.22 0.24 0.52 0.17 1.29 0.04 0.03 0.05 -0.41
58 7.3 0.29 0.21 1.45 0.45 0.14 0.95 0.27 5.07 0.05 0.09 0.21 -0.09
Table 6 Concentrations of trace elements in groundwater samples from Tibet
Sample number Li
(μg/L)		 Sr
(mg/L)		 B
(mg/L)		 Zn
(μg/L)		 Se
(μg/L)		 F
(mg/L)		 U
(μg/L)		 Rb
(μg/L)		 Ba
(μg/L)		 Co
(μg/L)		 Cs
(μg/L)		 Ga
(μg/L)		 V
(μg/L)
3 48.9 0.15 0.18 55.80 0.00 0.09 2.39 6.08 6.49 0.05 5.45 0.30 0.15
4 50.3 0.15 0.20 7.68 0.00 0.12 2.41 6.49 11.98 0.06 9.06 0.58 0.09
10 2.97 0.15 0.13 1.16 0.00 0.04 0.30 0.09 33.48 0.07 0.02 1.66 -0.08
11 1.15 0.09 0.02 21.54 0.00 0.06 0.21 0.07 25.74 0.04 0.16 1.33 -0.16
13 105 1.03 0.37 7.14 0.04 0.38 5.54 4.49 87.75 0.58 0.99 4.22 0.38
16 12.7 0.27 0.15 3.40 0.00 0.08 1.95 0.57 64.37 0.31 0.03 3.10 0.21
17 95.3 1.40 0.49 1.47 0.05 0.48 5.83 0.88 24.06 0.41 0.02 1.07 0.32
18 54.4 0.31 0.31 0.99 0.03 0.26 2.15 5.88 21.20 0.07 2.06 0.98 0.32
19 60.6 0.29 0.18 2.06 0.01 0.43 1.49 4.53 18.29 0.10 0.03 0.85 -0.27
20 85.0 0.27 0.18 10.43 0.00 0.27 0.24 5.68 53.84 0.65 0.02 2.54 -0.26
22 79.8 0.80 0.36 4.40 0.05 0.22 4.09 9.31 71.36 0.36 0.64 3.12 2.19
23 121.77 0.28 0.41 3.24 0.00 0.33 0.93 2.87 8.80 0.06 0.03 0.38 -0.04
24 24.6 0.45 0.32 2.00 0.03 0.10 2.93 1.01 60.78 0.34 0.01 2.70 0.20
25 39.9 0.88 0.22 4.79 0.08 0.19 1.65 2.14 73.71 0.09 0.04 3.24 -0.12
28 10.4 0.25 0.21 24.22 0.07 0.20 1.48 0.38 42.85 0.06 0.01 1.92 0.34
29 37.4 0.63 0.22 22.15 0.05 0.19 22.77 0.46 41.98 0.23 0.01 1.81 -0.06
30 35.7 0.26 0.31 2.90 0.05 0.33 1.44 1.19 26.70 0.05 0.04 1.18 0.13
31 745 1.64 2.92 18.34 0.04 3.05 0.42 82.40 94.15 0.28 85.13 4.50 -0.58
32 2658 1.96 8.61 1.94 0.13 7.24 0.06 190.64 75.57 0.10 428.09 3.33 0.10
33 1495 1.77 5.35 1.80 0.06 3.56 0.31 125.09 102.19 0.05 144.69 4.69 -0.22
34 295 0.86 1.18 2.47 0.15 1.34 1.45 33.29 104.00 0.11 48.34 4.75 0.81
37 29.9 0.47 0.60 6.76 0.75 0.27 13.46 2.93 33.63 0.10 15.38 1.44 -0.09
39 96.5 0.51 1.62 6.16 0.22 0.32 4.74 1.46 43.89 0.13 0.07 1.96 2.06
40 142 0.67 1.05 1.76 0.16 0.33 3.75 18.55 104.26 0.09 7.65 4.64 3.42
41 18.98 0.23 0.43 2.12 0.08 0.14 1.93 0.35 43.80 0.08 0.07 1.97 0.13
42 64.7 0.71 1.06 3.44 0.10 0.26 11.61 0.57 28.43 0.20 0.08 1.23 0.13
43 27.7 0.19 0.77 2.91 0.09 0.24 1.30 1.19 11.28 0.05 0.11 0.49 -0.23
45 55.0 0.79 0.60 2.59 0.24 0.39 2.71 3.17 25.84 0.09 1.66 1.11 -0.13
46 49.5 0.55 1.11 0.99 0.49 0.33 2.29 1.09 24.86 0.05 0.07 1.09 0.55
47 458 0.45 2.11 428.69 0.53 1.20 9.08 51.88 23.02 0.08 119.46 0.98 1.84
48 116 0.79 0.96 68.11 0.57 0.19 1.86 14.48 36.96 0.05 70.10 1.64 0.28
49 33.0 0.16 1.39 15.97 0.14 0.14 1.26 5.20 12.03 0.05 0.99 0.52 0.43
50 159 0.41 2.32 6.95 0.09 0.14 3.41 6.22 30.70 0.17 6.99 1.33 0.34
51 30.3 0.41 0.58 5.94 0.24 0.11 1.72 2.06 39.20 0.04 0.77 1.72 -0.01
55 14.2 0.46 0.07 3.80 0.11 0.04 2.27 0.25 9.52 0.15 0.04 0.39 -0.23
56 7.49 0.33 0.10 3.35 0.90 0.06 0.86 0.68 17.18 0.10 0.78 0.76 -0.25
59 3.12 0.12 0.09 1.19 0.18 0.07 0.43 0.43 6.84 0.04 0.45 0.28 -0.29
60 31.9 0.13 0.15 24.38 0.18 0.11 1.14 3.75 6.17 0.04 5.46 0.26 -0.47
Table 7 Concentrations of toxic elements in surface water samples from Tibet
Sample number Al
(μg/L)		 As
(μg/L)		 Be
(μg/L)		 Cr
(μg/L)		 Cu
(μg/L)		 Fe
(μg/L)		 Mn
(μg/L)		 Mo
(μg/L)		 Ni
(μg/L)		 Pb
(μg/L)		 Se
(μg/L)
1 3.26 1.10 0.05 6.77 0.31 76.00 0.09 1.56 0.71 0.00 0.00
2 0.37 2.05 0.04 10.71 0.21 106.38 0.06 0.72 0.93 0.01 0.20
5 0.59 89.38 0.06 9.79 -0.05 66.10 0.04 0.21 0.57 0.00 0.00
6 87.74 0.90 0.03 4.90 0.64 68.68 0.65 0.23 0.55 0.06 0.00
7 16.93 0.30 0.03 2.96 0.54 36.31 0.13 0.23 0.53 0.02 0.00
8 60.61 0.76 0.09 3.10 0.57 60.99 2.44 0.24 0.54 0.05 0.03
9 26.73 0.31 0.04 2.58 0.51 43.60 0.41 0.25 0.44 0.04 0.00
12 3.57 10.59 0.01 4.97 0.09 51.28 0.11 0.61 0.50 0.00 0.00
14 1.34 0.68 0.05 5.65 0.94 97.90 1.45 0.71 2.08 0.02 0.01
15 0.80 1.74 0.03 4.83 0.16 121.11 0.36 1.58 1.19 0.04 0.08
21 385.72 0.86 -0.02 6.87 0.78 251.87 2.75 0.27 1.23 0.25 0.02
26 4.52 1.51 -0.06 2.42 0.26 134.14 0.04 0.33 1.54 0.01 0.07
27 2.00 1.36 -0.04 2.01 0.38 167.27 0.34 1.06 2.02 0.02 0.01
35 0.98 1.63 -0.04 2.39 1.52 140.65 0.09 2.80 1.95 0.01 0.52
36 0.30 2.22 -0.04 6.03 0.86 50.03 0.11 0.80 0.51 0.05 0.25
38 2.20 2.96 -0.01 1.18 0.18 87.86 0.05 0.58 0.91 0.00 0.11
44 0.99 3.44 -0.07 1.09 -0.02 109.53 0.16 0.64 1.02 0.01 0.18
52 1.45 1.81 0.00 1.91 -0.03 146.57 0.13 0.34 1.86 0.01 0.85
53 84.26 0.73 -0.02 0.67 0.37 75.09 6.62 0.52 1.06 0.05 0.13
54 42.07 6.97 0.02 0.62 0.13 44.11 0.55 1.51 0.54 0.07 0.19
57 1.08 1.20 -0.05 1.08 -0.07 75.46 0.27 0.88 0.73 0.01 0.22
58 0.70 2.00 -0.08 8.40 0.08 91.71 0.11 0.44 0.87 0.01 0.45

4 Discussion

4.1 Hydrochemical characteristics

The water samples collected (except for sample numbers 20 and 30) were weakly alkaline (Tables 3 and 4) and the pH of these water samples met both the Chinese national standard and the international standard (WHO, 2004; MH, 2006) (Table 9). The TDS and TH in the natural waters of Tibet also met both the Chinese national standard and the international standard (WHO, 2004; MH, 2006). Some of the water samples also met the national Drink Natural Mineral Water Standard (GAQS, 2008) (samples collected from Kema village, Luoma town, Nagchu county; Marm town, Gerze county; and Baga town, Burang county; Table 9).

4.2 Toxic elements

Arsenic poisoning is a common endemic disease. The main symptom of arsenic poisoning is skin alteration, including dermal hyperkeratosis, verrucous keratosis and skin cancer (Smith, 1992). Some patients also experience gastrointestinal or hepatic dysfunction (Zhao et al., 2002). Studies have shown that the arsenic concentration in water is mainly affected by the underlying lithology (Qing et al., 2007). In Damxung, Shuanghu, Gerze, Geji and Seng-ge Kambab of northern Tibet, the arsenic concentration is high (Tables 7, 8 and 10). As a result, people who live in these regions may be affected by arsenic poisoning through drinking water. Therefore it is essential to carry out further research on endemic arsenic poisoning in these prefectures as well as on the distribution and genesis of water with a high arsenic concentration. The fluoride concentration in Shuanghu county exceeded both the Chinese national standard and the international standard (WHO, 2004; MH, 2006). The toxic elements in water from other regions meet both these standards, which means that water in these regions is suitable for drinking.
Table 8 Concentrations of toxic elements in groundwater samples from Tibet
Sample number Al
(μg/L)		 As
(μg/L)		 Be
(μg/L)		 Cr
(μg/L)		 Cu
(μg/L)		 Fe
(μg/L)		 Mn
(μg/L)		 Mo
(μg/L)		 Ni
(μg/L)		 Pb
(μg/L)		 Se
(μg/L)
3 0.19 1.96 -0.02 10.35 -0.04 98.39 0.07 0.96 0.77 0.01 0.00
4 0.46 3.10 -0.04 10.63 0.02 100.00 0.02 0.80 0.82 0.00 0.00
10 99.64 0.48 0.06 9.66 0.23 96.70 0.39 0.10 0.86 0.01 0.00
11 0.55 1.06 -0.04 8.46 -0.01 59.88 0.83 0.08 0.53 0.03 0.00
13 0.95 0.38 0.00 13.97 1.55 344.86 242.76 0.59 5.75 0.09 0.04
16 1.10 0.54 0.04 18.13 1.07 257.68 0.11 0.16 2.71 0.01 0.00
17 7.28 0.58 -0.01 12.06 0.88 238.17 0.09 0.39 2.61 0.01 0.05
18 33.97 5.09 0.05 3.48 0.62 78.13 0.30 0.67 1.60 0.02 0.03
19 0.75 0.64 -0.01 7.97 0.19 148.33 0.23 0.24 1.46 0.01 0.01
20 0.49 0.61 -0.07 16.32 0.04 143.27 514.97 0.21 1.84 0.01 0.00
22 1.15 1.05 -0.03 6.78 3.35 320.31 19.15 0.41 5.85 0.02 0.05
23 0.49 0.63 -0.03 4.62 0.50 112.17 0.55 0.15 1.13 0.01 0.00
24 0.30 0.47 0.02 4.87 0.84 269.51 0.11 0.10 3.46 0.01 0.03
25 0.26 1.20 -0.08 2.86 0.31 140.86 0.03 0.51 1.40 0.00 0.08
28 1.19 0.87 0.00 2.98 0.15 65.05 0.08 0.20 0.75 0.01 0.07
29 4.38 3.21 -0.08 3.77 0.59 246.08 0.55 0.91 2.45 0.02 0.05
30 0.44 1.54 -0.02 2.00 0.12 62.22 0.06 0.99 0.66 0.02 0.05
31 0.67 46.19 0.14 60.90 2.51 333.99 2.82 2.25 4.22 0.02 0.04
32 2.13 333.92 0.07 19.04 7.56 125.91 5.81 0.11 1.64 0.07 0.13
33 0.63 219.94 0.23 33.60 4.51 110.92 6.62 0.30 1.03 0.02 0.06
34 0.47 2.46 -0.03 9.48 0.82 155.70 0.20 0.58 1.60 0.02 0.15
37 0.45 1.29 0.00 3.63 0.94 156.06 0.06 2.19 1.79 0.01 0.75
39 0.62 6.81 -0.04 6.45 1.16 45.64 0.07 2.19 0.74 0.01 0.22
40 1.35 4.42 -0.05 1.84 0.53 107.69 0.04 0.59 1.25 0.01 0.16
41 1.27 3.77 -0.03 1.49 0.17 107.52 0.00 0.47 1.10 0.01 0.08
42 0.67 2.22 0.05 1.64 0.84 190.51 0.01 2.36 2.07 0.05 0.10
43 0.49 4.46 -0.04 1.20 0.13 65.08 0.01 0.54 0.65 0.01 0.09
45 0.47 1.28 0.04 3.68 0.04 188.20 0.04 1.06 1.89 0.01 0.24
46 0.43 3.03 -0.02 7.20 0.29 64.15 0.42 1.02 0.70 0.01 0.49
47 0.31 163.55 -0.06 1.50 0.74 89.59 0.94 6.02 0.98 0.02 0.53
48 0.68 57.96 -0.10 2.07 0.20 80.98 0.02 1.28 0.81 0.01 0.57
49 7.98 56.21 -0.03 0.81 0.06 64.30 0.00 0.98 0.65 0.01 0.14
50 0.91 17.48 0.02 1.61 0.30 122.64 0.13 0.59 1.82 0.01 0.09
51 0.63 1.09 -0.03 1.62 0.00 74.42 0.02 0.72 0.73 0.01 0.24
55 0.86 1.51 -0.04 5.66 0.12 238.44 0.11 0.36 2.18 0.01 0.11
56 21.45 3.56 -0.03 2.78 0.25 133.97 2.34 0.64 1.44 0.02 0.90
59 0.97 2.50 0.01 4.65 0.09 53.98 0.00 0.18 0.92 0.02 0.18
60 1.55 1.87 -0.03 1.02 0.00 65.49 0.62 1.34 0.75 0.01 0.18
Table 9 Major and trace element test standards for water quality
Parameter Standards for Drinking Water Quality (MOHC, 2006) Guidelines for Drinking Water Quality (WHO, 2004) Drink Natural Mineral
Water (AQSIQ, 2008)
pH 6.5-8.5 6.5-9.5 –
TDS (mg/L) 1000 1000 ≥1000
TH (mg/L) 450 500 –
Na+ (mg/L) 200 200 –
SO42- (mg/L) 250 500 –
Cl- (mg/L) 250 250 –
H2SiO3 (mg/L) – – ≥25.0
Li (μg/L) – – ≥200
Sr (mg/L) – – ≥0.2
B (mg/L) 0.5 0.5 <5
Zn (μg/L) 1000 3000 ≥200
Se (μg/L) 10 10 ≥10
F (mg/L) 1 1.5 <1.5
U (μg/L) – 15 –
Ba (μg/L) 700 700 <700

4.3 Hydrochemical characteristics

The ratio of major ions in water can be clearly shown with a Piper plot (Piper, 1944); the percentage of major ions determines the hydrochemical type of water (Chen et al., 2014; Piper, 1944; Shen et al., 2007; Zhu et al., 2011). The main hydrochemical types of water samples in Tibet are as follows: Ca-Mg-HCO3 (eight samples); Ca-Mg-HCO3-SO4 (eight samples); Ca-HCO3 (five samples); Ca-HCO3-Cl (three samples); Ca-Na-Mg-HCO3 (three samples); Na-Ca-HCO3 (three samples); Ca-Mg-HCO3-Cl (two samples); Mg-Ca-HCO3 (two samples); Na-HCO3 (two samples) (Figure 3; Tables 3 and 4).
Figure 3 Box and whisker plots showing the variation of major ion concentrations in water samples from Tibet
Table 10 Harmful element test standards for water quality
Element (μg/L) Standards for Drinking Water Quality (MOHC, 2006) Guidelines for Drinking-Water Quality (WHO, 2004) Drink Natural Mineral Water (AQSIQ, 2008)
Ag 50 100 <50
Al 200 200 –
As 10 10 <10
Be 2 – –
Cd 5 3 <3
Cr 50 50 <50
Cu 1000 2000 <1000
Fe 300 300 –
Hg 1 1 <1
Mn 100 400 <400
Mo 70 70 –
Ni 20 20 <20
Pb 10 10 <10
Se 10 10 <50
Tl 0.1 – –
The predominant cation and anion in the water samples from Tibet were Ca2+ and HCO3-, respectively. The major cations in water were Ca2+ > Na+ > Mg2+ > K+ and the major anions were HCO3- > SO42- > Cl- (Figure 4). From south to north, the main cation in water changed from Ca2+ to Na+, whereas the main anions in water changed from HCO3- to Cl- and SO42-. The surface runoff and groundwater in Tibet are recharged mainly by ice/snow melt water and rain.
The main water type in northern Tibet, in the Yarlung Zangbo river catchment, the Lhasa river catchment, the Nianchu river catchment, the Nyang river catchment and the internal flow lake basin area is pore water from loose rocks. Bedrock fissure water is mainly distributed from north of the Himalayas to south of the Changtse Mountains. Karst water is mainly distributed in the central and western Changtang Plateau.

4.4 Preliminary discussion on the causes of variation in Tibetan water samples

The boomerang envelope model developed by Gibbs (1970) describes three types of water: (1) water from evaporation/crystallization; (2) water dominated by rock type; and (3) water from atmospheric precipitation. The chemical composition of surface water in Tibet is mainly controlled by rock weathering (Figure 5).
Figure 4 Piper diagram showing the major concentrations of cations and anions in waters of Tibet by geological setting
Figure 5 Plots of the major ions within the Gibbs boomerang envelope for waters in Tibet
The control of the chemical composition of surface water in Tibet by rock weathering is consistent with results from elsewhere in the world, including the Yangtze River, the Amazon River and the Ganges (Gibbs, 1970). The results for groundwater in the Gibbs boomerang envelope plot are relatively fragmented, which suggests that the chemical composition of groundwater is diverse and complicated. As a result of the high temperatures, the concentrations of elements in the hot-spring waters are high and water samples are close to the seawater type in the Gibbs boomerang envelope.

4.5 Regional comparison

In order to explore the differences in the hydrochemical characteristics of different regions, we compared the average values for water samples collected from the Tibetan region with the average values for water samples collected from Southern Xinjiang, the Tongtian River in Qinghai, the Qinghai Lake Basin, Huanglong (Yellow Dragon), Maoxian county and Zamtang county of Sichuan, Yarlung Zangbo River between Lhasa-Nyingchi and Shegyla Mountain (Table 11).
Table 11 Hydrochemical characteristics in different regions of western China
Tibet Southern
Xinjiang		 Tongtian River Qinghai Lake Basin Huanglong Maoxian county Zamtang county Yarlung Zangbo River between Lhasa-Nyingchi Shegyla Mountain
Number of samples 57 154 9 75 9 63 423 62 9
pH 7.55 7.64 8.09 8.09 6.59 7.7 7.43 7.74 7.46
K+ 3.09 17.87 6.77 1.87 0.4 2.36 14.25 3.16 0.14
Na+ 34.93 336.97 118.02 36.42 3.14 19.12 4.89 0.03
Ca2+ 55.25 90.1 51.77 37.38 253.78 70.36 33.77 29.74 1.6
Mg2+ 18.69 73.78 18.82 16.04 20.94 28.38 10.4 5.56 3.82
Cl- 47.67 509.41 179.88 47 0.73 7.37 3.9 3.87 7.41
SO42- 54.68 429.08 83.34 39.35 23.2 119.6 8.05 25.83 62.52
HCO3- 169.67 260.28 170.63 183.37 777.44 226.27 171.21 90.28 33.9
Reference This study Liu et al. (2014),
Pang et al. (2010), Zhang et al. (1995)		 Su et al. (1987) Xu et al. (2010) Wang et al. (2009) Du (2011) Cao (2011) Liu (2011) Ren et al. (2002)
The hydrochemical types of the Southern Xinjiang, Qinghai Tongtian River, Lake Qinghai catchment, Sichuan Yellow Dragon, Sichuan Maoxian county, Sichuan Zamtang county, Yarlung Zangbo River between Lhasa and Nyingchi and Shegyla Mountain are: Na-Mg-Cl-SO4, Na-Ca-Cl-HCO3, Ca-Na-Mg-HCO3-Cl, Ca-HCO3, Ca-Mg-HCO3-SO4, Ca-Mg-HCO3, Ca-Mg-HCO3-SO4 and Mg-SO4-HCO3, respectively. It can be inferred that different locations lead to different hydrochemical types (Table 11 and Figure 6).

5 Conclusions

The data obtained in this study are representative of the natural hydrochemical characteristics in Tibet as a result of the limited human activities in this region. The water quality in most regions of Tibet is good and meets both the Chinese national standard and the international standard (WHO, 2004; MH, 2006). Some of the water samples also met the national Drink Natural Mineral Water Standard (GAQS, Inspection and Quarantine of the People’s Republic of China, 2008). The arsenic and fluoride concentrations in Damxung, Shuanghu, Gerze, Geji and Seng-ge Kambab of northern Tibet are higher than those specified in the Chinese national standard and the international standard (MH, 2006; WHO, 2004).
Figure 6 Piper diagram showing major ion compositions of natural water in different regions of western China
The results of this study can be summarized as follows.
(1) The pH value of water samples ranges from 6.75 to 8.21 and most of the water samples are weakly alkaline.
(2) The mean value of TDS in water samples is 225.54 mg/L, except for the hot-spring water samples. Therefore the majority of water in Tibet is suitable for drinking.
(3) The arsenic concentration in water samples from Ali prefecture and the fluoride concentration in water samples from Shuanghu exceed both the Chinese national standard and the international standard (WHO, 2004; MH, 2006). Further studies are needed on fluorosis and endemic arsenic poisoning resulting from drinking water.
(4) The dominant ions in water from Tibet are Ca2+ and . The main hydrochemical types of Tibetan water are Ca-HCO3, Ca-Mg-HCO3 and Ca-Mg-HCO3-SO4. From south to north, the main cation in water changes from Ca2+ to Na+, whereas the main anions in water change from to Cl- and .
(5) River water and ice/snow melt water are dominated by the rock type and the formation of groundwater is affected by many factors. The element concentrations in hot-spring water are high and are similar to seawater.

The authors have declared that no competing interests exist.

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