Abstract
PurposeTo understand the impact of geochemical sedimentation history for arsenic (As) distribution in the sediment profiles of the Hetao Basin, we (1) evaluated sediments provenance and variations of weathering intensities, (2) attempted to reconstruct the depositional environments, and (3) explored the As and Fe speciation in the sediments. Combining the information above, different sedimentation facies were distinguished in the vertical profiles.MethodsTwo sediments cores were drilled up to 80 m depth. Major and trace element compositions, including rare earth elements (REE), were analyzed. Carbon isotope ratios (δ13Corg) of embedded organic matter in the sediments were analyzed by isotope ratio mass spectrometry (IR-MS). Arsenic and Fe speciation of the sediments were determined by sequential extractions.Results and discussionThe similar REE geochemistry of rocks from the Lang Mountains and sediments in the Hetao Basin indicated that the sediments originated from the Lang Mountains. The C/N ratio (~ 4 to ~ 10) in combination with δ13Corg (− 27‰ to −2 4‰) suggested that sediments were mainly deposited in aquatic environments. The unconfined aquifer equaled the lacustrine deposit with less intensive weathering during last glacial maximum (LGM). Here, the As content (average, 5.4 mg kg−1) was higher than in the aquifer sediments below (average, 3.6 mg kg−1).ConclusionHigher content of releasable As in combination with paleolake-derived organic matter aquifer sediments probably contributes to higher groundwater As concentration in the unconfined aquifer. This study provides the first insight into the impact of sedimentation history on As distributions in sediment profiles in the Hetao Basin.
Highlights
IntroductionGeogenic groundwater arsenic (As) contamination is of global concern
Responsible editor: Tomas Matys GrygarElectronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Geogenic groundwater arsenic (As) contamination is of global concern
The similar rare earth elements (REE) geochemistry of rocks from the Lang Mountains and sediments in the Hetao Basin indicated that the sediments originated from the Lang Mountains
Summary
Geogenic groundwater arsenic (As) contamination is of global concern It is mainly reported from floodplains in South and Southeast Asia including the Ganges-Brahmaputra-Meghna (GBM) River delta, the Mekong River delta, the Red River delta, and inland basins located in the Yellow River catchment including the Hetao Basin, the Hohhot Basin, the Datong Basin, and the Yinchuan Basin (Nordstrom 2002; Rodríguez-Lado et al 2013; Guo et al 2017). Over 100 million people are exposed to As with concentration higher than 10 μg L−1 (the World Health Organization standard) in the drinking water (Ravenscroft et al 2009). Studies indicate that in situ microbial organic carbon oxidation processes coupled with reduction of As-bearing Fe oxy(hydr)oxides is the main cause for As release into groundwater
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