Dynamic research on source and distribution of PAHs in the Qingshuiquan underground river

• 發表在: Carsologica Sinica
• Main Authors: Zhe WANG, Jiang LI, Li LU, Riyuan XIA, Jianwen CAO, Liangjie ZHAO, Song LUAN
• 格式: Article
• 語言: 英语
• 出版: Institute of Karst Geology,Chinese Academy of Geological Science 2023-04-01
• 主題: polycyclic aromatic hydrocarbons; underground river; source; partition; dynamic law
• 在線閱讀: http://zgyr.karst.ac.cn/article/doi/10.11932/karst2022y15?pageType=en

In recent years, the groundwater pollution of polycyclic aromatic hydrocarbons (PAHs) in Nanning City has been increasingly serious due to the acceleration of urbanization in this city and its dual water-bearing structure of underground and surface as well as the properties of PAHs. As a major source of drinking water for the city, the Qingshuiquan underground river plays an important role in the local economic and social development. Therefore, more research on PAHs pollution in Naning City is needed.Covering an area of about 55.3 km2, the Qingshuiquan underground river is located in the northwest of Nanning. The strata distributed in the area are mainly upper Carboniferous (C3), Lower Cretaceous (K1) and Paleocene (E1), and the lithology is mostly thick bedded limestone. There are two underground river pipelines in the area. The groundwater mostly flows from east to west in the way of pipeline flow, and is discharged from the surface in the form of underground river outlet at S15 and flows into the Bachi river. At present, with an annual water supply capacity of 19 million square meters, the Qingshuiquan underground river provides drinking water for Yongning district of Nanning City, and is an important source of drinking water in Nanning City. In the upper reaches of the system, pollution is mainly from agricultural and domestic pollutants. In its middle and lower reaches, pollution is mainly generated from industrial enterprises, including cement plants, paper mills, quarries and gas stations.Based on the previous test data and the sampling data of this study, the research is mainly focused on the distribution rule of PAHs with the Qingshuiquan underground river as the research object. The statistics method, isomer ratio method, distribution coefficient method and others were adopted to analyze the content, distribution characteristics and source change of PAHs in water environment over the years. Results showed that, (1) The PAHs content with different ring numbers in groundwater were in the order of 4>3>5>2>6, mainly with low ring (2-3); the content of PAHs with different ring numbers in sediment were in the order of 4>5>3>6 >2, mainly with high ring (4-6). The PAHs content in groundwater experienced an increase after a decrease, but the content in sediment saw a gradual increase, which reflected different dynamic characteristics of PAHs content in groundwater and sediment due to the urbanization and industrialization in Nanning City. (2) The spatial distribution of PAHs content in water environment was listed as follows, upstream content<middle stream content<downstream content, which may be caused by the increase of industrial pollution sources as well as PAHs emissions from upstream to downstream. The variation trend of PAHs content in groundwater in different regions was different. The content of PAHs in groundwater increased gradually in the upstream, stabilized initially and then increased sharply in the middle, and decreased first and increased afterward in the downstream. The content of PAHs in sediments of different regions presented the same trend of a gradual increase, but the increase rate was different. (3) There are also differences between the change rules over the years. The PAHs sources at upstream reaches has been generated by biomass burning, and have changed from petroleum source to the mixed one at middle reaches. At downstream, the PAHs sources has changed from fossil fuel combustion to primarily mixed source. These changes are mainly attributed to different types of pollution sources and their emissions in different areas. (4) Kp values of different ring numbers were in the order of 6>5>4>3>2. Kp values gradually increased with rise of ring numbers, and PAHs with larger ring numbers tended to be adsorbed by sediments. The lgKoc values of PAHs at S11-S15 sampling sites all exceeded the upper limit and were distributed in downstream, showing a strong adsorption capacity of PAHs on particulate matter. The lgKoc values of the remaining sampling sites are below the upper limit, reflecting the influence of dissolved organic matter on the distribution of PAHs.