Abstract
Temporal variations in water levels are crucial for understanding As behaviour in groundwater systems. Groundwater levels were recorded in irrigation wells in non-irrigation and irrigation seasons. Groundwater samples were collected yearly in irrigation wells from 2014 to 2016 and in a multilevel well from 2015 to 2016 for analysing geochemical parameters. Results showed that groundwater flow direction was reversed due to groundwater pumping. The change of groundwater flow led to the surface water, as a new groundwater recharge source, which flushed the near-surface sediments enriched in soluble components and increased groundwater TDS. The labile organic matter introduced by the surface water recharge fueled dissimilatory reduction of Fe(III) oxides and further increased groundwater As concentration.
Highlights
High arsenic(As) groundwater has been found worldwide [1]
This study aims at characterizing relationships between variations in groundwater flow pattern and groundwater chemistry and understanding effects of the extraction on groundwater As dynamics
Prior to the extensive groundwater extraction, groundwater mainly flowed from alluvial fans to the flat plain and discharged into the Shahai lake and the drainage channel
Summary
High arsenic(As) groundwater has been found worldwide [1]. Some studies showed that groundwater extraction affected groundwater As via the changes of groundwater recharge source, the anomalous disturbance of sediments and the vertical groundwater mixing [2-5]. Previous studies showed that the reductive dissolution of Fe(III) oxyhydroxides led to As release from aquifer sediments in the Hetao basin [6-7]. This study aims at characterizing relationships between variations in groundwater flow pattern and groundwater chemistry and understanding effects of the extraction on groundwater As dynamics. The study area is located in the northwest of the Hetao basin, including alluvial fans and flat plain (Fig. 1). According to our borehole loggings, shallow groundwater was considered to be hosted in aquifers overlying the clay layers around 40 m below land surface (BLS), while aquifers underlying the clay layers, being regarded as the semi-
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