Influences of groundwater extraction on flow dynamics and arsenic levels in the western Hetao Basin, Inner Mongolia, China

Zhang, Zhuo; Guo, Huaming; Zhao, Weiguang; Lichuanjushi,; Cao, Yongsheng; Jia, Yongfeng

Influences of groundwater extraction on flow dynamics and arsenic levels in the western Hetao Basin, Inner Mongolia, China | Influence de l’exploitation des eaux souterraines sur la dynamique des écoulements et les concentrations en arsenic dans l’ouest du bassin de Hetao, Mongolie intérieure, Chine Influencias de la extracción de agua subterránea en la dinámica del flujo y en los niveles de arsénico en la cuenca occidental de Hetao, Mongolia Interior, China 中国内蒙古河套盆地西部地下水开采对水流动力特征和砷含量的影响 Influências da extração de águas subterrâneas na dinâmica do fluxo e níveis de arsênio na Bacia do oeste de Hetao, Mongólia Interior, China

2018

Data on spatiotemporal variations in groundwater levels are crucial for understanding arsenic (As) behavior and dynamics in groundwater systems. Little is known about the influences of groundwater extraction on the transport and mobilization of As in the Hetao Basin, Inner Mongolia (China), so groundwater levels were recorded in five monitoring wells from 2011 to 2016 and in 57 irrigation wells and two multilevel wells in 2016. Results showed that groundwater level in the groundwater irrigation area had two troughs each year, induced by extensive groundwater extraction, while groundwater levels in the river-diverted (Yellow River) water irrigation area had two peaks each year, resulting from surface-water irrigation. From 2011 to 2016, groundwater levels in the groundwater irrigation area presented a decreasing trend due to the overextraction. Groundwater samples were taken for geochemical analysis each year in July from 2011 to 2016. Increasing trends were observed in groundwater total dissolved solids (TDS) and As. Owing to the reverse groundwater flow direction, the Shahai Lake acts as a new groundwater recharge source. Lake water had flushed the near-surface sediments, which contain abundant soluble components, and increased groundwater salinity. In addition, groundwater extraction induced strong downward hydraulic gradients, which led to leakage recharge from shallow high-TDS groundwater to the deep semiconfined aquifer. The most plausible explanation for similar variations among As, Fe(II) and total organic carbon (TOC) concentrations is the expected dissimilatory reduction of Fe(III) oxyhydroxides.

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