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

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 (HCO 3 ) 2 . From south to north, the main cation in water changes from Ca 2+ to Na + , whereas the main anions in water change from HCO 3 -to Cl -and SO 4 2-. 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.

Distribution and Potential Health Risks of Arsenic, Selenium, and Fluorine in Natural Waters in Tibet, China

“…The chemical composition of Tibet waters is mainly controlled by rock weathering (Figure 7), which is consistent with other studies led in Tibet [3] and other places of the world, including the Yangtze River, the Amazon River, and the Ganges [32]. The Gibbs boomerang envelope plot shows that the main process controlling the composition of streams is rock weathering.…”

“…Most stream and well waters are slightly alkaline, with an average pH of 7.8, and the dominant cation and anion in these water samples are Ca 2+ and HCO 3 − , respectively. The mean value of TDS in water samples is 213.0 mg/L; therefore, the majority of natural waters in Tibet are suitable for drinking.…”

“…Li et al [5] found very high concentrations of arsenic in waters from two hot springs and seven alkaline salt lakes in western Tibet, reaching maximum values of 5985 μg/L and 10,626 μg/L, respectively. Tian et al [3] also reported nine water samples with high arsenic levels (mean value 113.23 μg/L) in Damxung, Shuanghu, Gerze, Geji, and Seng-ge Kambab in northern Tibet and low selenium concentrations (maximum of 0.898 μg/L and mean of 0.154 μg/L) in all water samples collected in central and western Tibet (n = 60). Guo and Wang [7] analyzed 30 drinking water samples from Sangri, Nyêmo, Xaitongmoin, and Gongbo'gyamda counties.…”

“…The average arsenic concentrations in the different types of water are, in decreasing order ( Figure 3 In addition to displaying high levels of As, Na + and HCO 3 − are the dominating major cation and anion, respectively, for three hot spring water samples (Table S1) The arsenic concentrations measured in the hot spring waters of Chongga village, Gongtang township, and Damxung county (30.59011 • N, 91.24375 • E, altitude: 4300 m, temperature: 50 • C) are very low, at 3.0 µg/L. In lake waters, arsenic concentrations ranged from 6.4 to 54.9 µg/L (Table S1), with an average of 27.5 µg/L.…”

“…In recent years, several studies have reported the hydrochemical characteristics of natural waters in Tibet [2,3] and the associated distribution of arsenic (As) [4][5][6], selenium (Se) [7][8][9][10] and fluorine (F) [11][12][13][14][15]. Wang et al [4] showed that arsenic concentrations exceeded 10 µg/L in 43.2% of stream water samples, as well as in all the samples from hot springs, saline lakes, well waters of the Seng-ge areas, and other drainage basins.…”