Abundant Fe(III) Oxide‐Bound Arsenic and Depleted Mn Oxides Facilitate Arsenic Enrichment in Groundwater From a Sand‐Gravel Confined Aquifer

Abstract

High arsenic (As) groundwater (>10 μg/L) has been increasingly observed throughout the world (Bundschuh

Dissolved Organic Matter Sources in High Arsenic Groundwater From a Sand‐Gravel Confined Aquifer

“…However, the sources and characteristics of DOM in shallow and deep groundwater were poorly understood. Under this direction, a continuation of the previously reported works in the area (Gao et al, 2022;Guo, Zhang, et al, 2014) was formed here. The main goal of our approach is to (a) identify sources and molecular compositions of shallow and deep groundwater DOM, (b) estimate a paradigm describing groundwater DOM processing pathways under reducing conditions, and (c) reveal linkages of sources and degradation state of DOM with groundwater As enrichment in the deep aquifer.…”

“…The release of sedimentary WSOM was likely related to Fe(III) oxide reduction (Mladenov et al., 2010), which occurred considerably more in the deep aquifer than in the shallow one (Gao et al., 2022). The contents of the extracted Fe(II) minerals in deep sediments (average 12.3 mmol/kg), possibly reflecting the extent of Fe(III) oxide reduction, were around two‐fold as high as those in shallow sediments (average 5.68 mmol/kg) (Gao et al., 2022). Previously reported works in the literature have revealed that WSOM in sediments were higher in BIX values (Huang et al., 2015) and labile OM abundances (Qiao et al., 2020) than groundwater DOM.…”

“…An increased DOM degradation releases more HCO 3 − into groundwater, and produces more energies and electrons for redox processes (CH 2 O + 2H 2 O → HCO 3 − + 5H + + 4e − ; Postma et al., 2016; Zhou et al., 2018). In the study area, the deep aquifer contained little amount of Mn oxides in sediments (Gao et al., 2022) and low concentrations of NO 3 − and SO 4 2− in groundwater (Table S1 in the Supporting Information ), which thus facilitated a greater extent of Fe(III) oxide reduction and As release. This result is also compatible with the much higher contents of extractable Fe(II) minerals in deep sediments (average 12.3 mmol/kg) than those in shallow sediments (average 5.68 mmol/kg) (Gao et al., 2022).…”

“…The chemical extraction methods for different solid pools of Fe, Mn, and As in sediments have been reported by Gao et al. (2022).…”

“…More details on sediment collection can be found in the Supporting Information (Text S3 in the Supporting Information S1). The chemical extraction methods for different solid pools of Fe, Mn, and As in sediments have been reported by Gao et al (2022).…”