One century sedimentary records of polycyclic aromatic hydrocarbons, mercury and trace elements in the Qinghai Lake, Tibetan Plateau
Introduction
Recently, distribution and fate of persistent organic pollutants (POPs) in mountain region and high Plateau have attracted increasing attention. The strong valley wind is able to dissipate POPs into mountain environment and the cold temperature would promote the deposition of POPs, namely “cold-condensation” (Daly and Wania, 2005). The “global distillation” hypothesis suggests that POPs tend to distribute from tropical point source to high-latitude areas via single-hop pathway or multi-hop pathway (Mai et al., 2003). Although the mechanism and role of high mountains during this global transport of POPs have been investigated (Daly and Wania, 2005, Chen et al., 2008, Wania and Westgate, 2008), studies focused on POPs deposition history in mountain regions are still very scarce (Daly et al., 2007, Chen et al., 2008). Distribution of sedimentary polycyclic aromatic hydrocarbons (PAHs) in industrialized region has been intensively studied and numerous studies documented the PAHs in sediments are effective proxies for the revelation and reconstruction of industrialization and urbanization (Liu et al., 2008, Hori et al., 2009, Li et al., 2009 Walker et al., 2004, Yim et al., 2005). While, limited sedimentary PAH data were published for remote areas (Barra et al., 2006), mostly in Arctic (Macdonald et al., 2000, Jiao et al., 2009), Antarctic (Martins et al., 2010) and European countries (Rose and Rippey, 2002, Vives et al., 2004). Similarly, although metal pollution has been extensively studied in coastal/industrial environments, little is known about the remote environment (Han et al., 2007, Usenko et al., 2007, Yang et al., 2010). China has undergone rapid economic development in the past three decades with an average annual Gross Domestic Product (GDP) growth rate of over 10%. Large amount of hazardous components, including PAHs, Hg and trace elements generated during industrialization may potentially move to remote/colder regions and therefore contribute to the contamination of pristine environment.
The Qinghai Lake (36°32′–37°15′ N, 99°36′–100°47′ E) is the largest saline lake in China. It is located about 100 km west of the provincial capital of Xining at 3225 m above sea level (Fig. 1). Local human activities around the Qinghai Lake basin are very limited. Therefore, sediments in Qinghai Lake archive important information about past anthropogenic influence. Jin et al., (2009a) investigated the 250-year sediment history of Pb in Qinghai lake and found that the average anthropogenic Pb deposition rate in Qinghai Lake since the 1960s was 12.2 ± 3.5 mg m−2 yr−1, which is comparable to averaged atmospheric Pb fluxes in the northern hemisphere. Qinghai Lake is adjacent to Gansu and Qinghai province of China, where industrialization and urbanization have been occurred. The pillar industries in Qinghai and Gansu province depend largely on petroleum production, hydropower generating industry, nonferrous metal industry and saline chemical industry (http://news.alibaba.com/article/detail/business-in-china/100085649-1-province-introduction-china%253A-gansu.html). In summer, Indian Monsoon, Eastern Asia Monsoon and westerly wind dominant the air circulation pattern over the Qinghai Lake. Thus, the atmospheric input of pollutants from neighbor region may lead to the contamination of the lake environment. However, less study has been conducted to evaluate the historical sediment record of PAHs and Hg in Qinghai Lake.
The objectives of the present study were to (1) examine the distribution of sediment PAHs, Hg and trace metals in the Qinghai Lake; (2) elucidate potential input sources of PAHs. To accomplish these objectives, we collected and analyzed sediment from the central areas of Qinghai Lake. Historical pollution data would be very useful in understanding the impact of economic development on the remote environment of the Qinghai Lake.
Section snippets
Study area and sample collection
Qinghai Lake is subject to a cold and semi-arid continental climate, i.e., cold and strong wind (≥18 m/s) in winter with strong westerly wind breezes from Qaidam Basin, where dust activities are prevalent. Average ambient temperature ranges from −5 to 8 °C all year around and an annual volume of rainfall ranges from 250 to 550 mm (Jin et al., 2009a, Jin et al., 2009b). The drilling site is located at 100.15°E and 36.43°N (Fig. 1). Water depth of the drilling site is 25.3 m. The sediment core
Abundance and flux of PAHs
Concentrations and depositional fluxes of PAHs in sediment core were presented in Fig. 2. Total concentrations of PAHs ranged from 15 to 341 ng g−1 (dry weight). Taking into account the USEPA proposed 16 priority PAHs, concentrations of all these 16 PAHs were in the range of 11–279 ng g−1 (dry weight). Depositional fluxes of total PAH were 0.3–14 ng cm−2 yr−1, while the fluxes of EPA 16 PAHs were from 0.2 to 11.2 ng cm−2 yr−1. The surface samples showed the higher concentration/flux values for
Conclusion
Increased level of PAHs, Hg, As, Pb and Zn in up-most sediment of Qinghai Lake reflect energy usage changes and follow closely the historical economic development in western China. This study on remote lake can help the environmental researchers to understand the global tendency of pollution. Qinghai Lake is located on the northeastern Tibetan Plateau, apparently, historical deposition trends of organic/inorganic pollutants in sediments from other part of the Tibetan Plateau are worthy to be
Acknowledgement
This study was supported by the Innovation Program of Chinese Academy of Sciences (KZCX2-YW-146), National Natural Science Foundation of China (40871233) and the Leverhulme Trust project “Lake sediment evidence for long-range air pollution on the Tibetan Plateau”(Project F/07 134BF).
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