Geological and Geochemical Characteristics of Low-Arsenic Groundwater in the Karamay Area Between Two High Arsenic Areas of Xinjiang, China
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Geological and Geochemical Characteristics of Low-Arsenic Groundwater in The Karamay Area Between Two High Arsenic Areas of Xinjiang, China Qiao Li ( [email protected] ) Xinjiang Agricultural University https://orcid.org/0000-0002-1514-8572 Hongfei Tao Xinjiang Agricultural University Mahemujiang Aihemaiti Xinjiang Agricultural University Youwei Jiang Xinjiang Agricultural University Wenxin Yang Xinjiang Agricultural University Jun Jiang Xinjiang Agricultural University Research Article Keywords: Low arsenic groundwater area, Tectonic and sedimentary evolution, Groundwater geochemistry, Xinjiang, China Posted Date: May 10th, 2021 DOI: https://doi.org/10.21203/rs.3.rs-498060/v1 License: This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License Page 1/15 Abstract The groundwater of several regions in Xinjiang, China, including the Kuitun and the Manas River Basins in the Junggar Basin, is heavily polluted with arsenic. However, the arsenic content of the groundwater of the Karamay area located within the Junggar Basin is relatively low and below the recommended drinking water limit. In our study, we analyze the factors that result in this anomaly. The geological and geochemical characteristics of the water-bearing system in this area were investigated by analyzing water samples, carrying out hydrogeological surveys, and statistical techniques. Since the Carboniferous, the geological development and subsequent structural evolution resulted in a lower arsenic concentration in groundwater of the Karamay region than that of the Kuitun River Basin and the Manasi River Basin. The missing high-energy sedimentary environment in the Middle-Upper Permian and the composition of sediments controlled the characteristics of the multi-layer aquifer in this area. We nd that the lack of arsenic sources, neutral and slightly alkaline environment, water injection to extract oil, and the Irtysh River Diversion to Urumqi Project, result in better groundwater quality and lower arsenic pollution in this area. 1. Introduction Arsenic (As) is a toxic element that is widely distributed in the environment (Guo et al. 2013). The formation of arsenic in groundwater is related to the geology and geomorphology (Nordstrom. 2012). Prolonged exposure to high levels of arsenic can cause cancer, cardiovascular diseases, nerve damage, and other diseases (He et al. 2020). Polluted drinking water (in countries such as Argentina, China, India, Bangladesh, the United States, Mexico, and Chile) is one of the primary routes through which people get exposed to arsenic (Tweed et al. 2020). Therefore, it is crucial to understand the geological and geomorphological factors that regulate the mobilization, chemical form, and fate of arsenic in groundwater. In the 1970s, people residing in the Kuitun river basin started drinking groundwater polluted with arsenic instead of clean river water. The noticeable decline in the health of the residents led to the discovery of China’s rst large-scale endemic arsenic poisoning in the 1980s (Hong. 1983; Yu et al. 2006; Wang et al. 1983). Later studies indicated that the arsenic content in groundwater of the adjacent Manas River Basin ranged from 0.003–0.491 mg/L, with an average of 0.011mg/L (Zhou et al. 2017), which exceeded the limit of arsenic in drinking water stipulated by China (Ministry of Health, PRC. 2006)and the World Health Organization: 0.01 mg/L (World Health Organization. 2011). The high arsenic content in the Kuitun River Basin is mainly caused by abundant metal reserves (the gold, copper, and pyrite-bearing sand deposits on the southern slope of the Mount Zhayier in the north and the northern slope of Yilianhabierga Mountain in the south) and geological conditions favorable for enrichment (most of the high-arsenic groundwater is distributed in the Chepaizi Depression, an artesian basin with very gentle strata as well as topographic altitude) (Li et al. 2017). On the other hand, high levels of arsenic in the groundwater of the Manas River Basin can be attributed to arsenic-rich coal seams such as the Honggou Coal Mine and the Xiaogou Coal Mine in the southern mountainous regions of the study area (Luo et al. 2017; Luo et al. 2006; Guo et al. 2013). Besides, the weakly permeable aquifer and ne-grained sediments in the high-arsenic groundwater areas lead to the further enrichment of arsenic in groundwater (Zeng et al. 2018). Zhou et al. investigated the spatial variations in the distribution of arsenic in the groundwater in Xinjiang, China (Zhou et al. 2017). They found that high- arsenic groundwater is mainly distributed in the Barkol-Yiwu Basin, Chepaizi area, Tarim Basin, and Yanqi Basin, excluding the Karamay area. The arsenic levels in the groundwater of the Karamay region is lower than the limit for arsenic in drinking water stipulated by China and the World Health Organization despite being located between the heavily polluted Kuitun and the Manas River Basins. The environmental (such as alluvial plains, sand dunes), hydrogeological and geochemical factors that result in this anomaly are poorly understood. More investigation is needed to understand the geological and geochemical characteristics that result in low-arsenic levels in this area (Giacobone et al. 2018). This paper takes the Karamay area between the Kuitun River and the Manas River basin as the study area. The water quality of the Dushanzi Reservoir, one of the water sources in the study area that uses groundwater as its water source, is evaluated as Class I water (Zhu et al. 2017). The largest urban area corresponds to the Karamay City, which is located in the northwest of the study area, with a population of more than 400,000 (Sixth National Population Census of the People’s Republic of China, 2010) (National Bureau of Statistics, PRC. 2011). The biggest threat to groundwater quality in the study area originates in human pollution and excessive exploitation of groundwater resources. Anthropogenic pollution in some areas has caused total dissolved solids in groundwater to reach 2.8 g/L (Li et al. 2011). The objective of this study is to analyze the possible tectonic, depositional, and geochemical processes that lead to low arsenic concentration in groundwater of the Karamay study area under the background of two high-arsenic watersheds. We collect groundwater samples and measure the existing aquifer composition. Further, we analyze the sediment origin, geological structure evolution, aquifer hydraulics, groundwater geochemical characteristics. We also characterize the spatial distribution of groundwater arsenic concentration in the Karamay area using a map. The growing global population has resulted in a simultaneous increase in the demand for clean water resources. Our study highlights the importance of better understanding the natural processes that create conditions conducive for good-quality groundwater, which is especially relevant for arid areas like Xinjiang. 2. Materials And Methods 2.1 Study area Location formation of the Karamay area The Karamay area is located on the northwestern margin of the Junggar Basin, between the Kuitun and Manas River Basins (Fig. 1). It is a well-known oil exploration site in China. The Zhayier Mountain lie to the northwest of the study, while the Manas Lake Depression lie to the northeast. The Zhongguai salient, Hongche Fault Zone and Dabasong salient lie to the south of the study area. The map in this gure was modied after Zhou Y et al.(2017) with permissions of Page 2/15 Elsevier (https://www.sciencedirect.com/science/article/abs/pii/S088329271630302X through QGIS—software (version 3.14.16); https://eur03.safelinks.protection.outlook.com/? url=https%3A%2F%2Fwww.qgis.org%2Fen%2Fsite%2F&data=04%7C01%7C%7Ca2eff60fe9454196008a08d8b0b20556%7C5b406aaba1f14f13a7aadd573da3 license Creative Commons Attribution-ShareAlike 3.0 licence (CC BY-SA). Geology and stratigraphy of the Karamay area With the development and evolution of the PaleoAsian Ocean in the Neoproterozoic, the junggar region and its adjacent areas nally formed the basement in the late Paleozoic, then deposit carboniferous and quaternary cap. The basement of the early Paleozoic in the study area is composed of volcanic arc rock, turbidite and ophiolite. (Buckman and Aitchison, 2004; Choulet et al., 2012). The carboniferous system in the sedimentary cover is mainly distributed on both sides of The Wuxia fault. The lower Carboniferous is relatively intact, and the lithology is mainly basalt, andesite, pyroclastic rock, siliceous rock, mudstone. The upper Carboniferous is mainly distributed around The Hararat Mountains, and the lithology is mainly volcanics, intermediate basic volcanic rocks, mudstones, sandstones and limestone lens bodies.The Permian is only developed in the lower Permian, which is distributed in a small amount near the Wuxia fault in a ne band. The lithology is basal conglomerate and sand conglomerate. The Triassic is developed in the upper Triassic, distributed in ne strips in the north of Karamay and unconformably in contact with Jurassic. The lithology is mainly sandy mudstone, conglomerate and sandstone. Jurassic outcrop is relatively complete, distributed around Karamay, lithology is mainly conglomerate, sandstone, mudstone and coal seam. The lower Cretaceous is exposed in the east of Karamay, unconformably in contact with Jurassic, and its lithology is conglomerate, sandstone and mudstone. The study area lacks upper Cretaceous, Paleogene and Miocene. The upper Holocene - quaternary series