Quantifying Geochemical Processes of Arsenic Mobility in Groundwater From an Inland Basin Using a Reactive Transport Model

Abstract

High arsenic (As) groundwater is frequently found in inland basins, yet the contributions of different processes to aqueous As distributions remain unresolved. In the Hetao Basin, a typical inland basin, groundwater As concentrations generally increased from the alluvial fan through the transition area to the flat plain. A geochemical process‐based reactive transport model was established to evaluate and quantify the processes of As mobilization in the northwestern Hetao Basin. Thirty‐six groundwater samples and eight sediment samples were collected from the alluvial fan to the flat plain to investigate the geochemical characteristics of the groundwater system. Along the approximate flow path, groundwater evolved from oxic‐suboxic conditions to anoxic conditions, with increasing concentrations of As, Fe (II), and NH4+, and decreasing Eh and SO42−/Cl−. Modeling results indicated that the observed concentrations of Fe (II) were caused by reductive dissolution of Fe (III) oxides and subsequent precipitation of mackinawite and siderite. Reductive dissolution of Fe (III) oxides was primarily driven by organic matter degradation (>75%), followed by H2S oxidation (<25%). More As was sequestered by mackinawite precipitation and adsorption than that released via abiotic reduction of Fe (III) oxides by H2S. Reductive dissolution of Fe (III) oxides was the dominant mechanism for liberating As in both the transition area and the flat plain (>70%), and As desorption under elevated pH and competitive adsorption by HCO3− and PO43− made an important contribution to As enrichment (up to 30%). Overall, this study provides an insight into the relative contributions of different geochemical processes to As enrichment in inland basins.

Conceptual Model of Arsenic Mobility in the Shallow Alluvial Aquifers Near Venice (Italy) Elucidated Through Machine Learning and Geochemical Modeling

“…Identifying a valid site‐specific conceptual model able to describe As mobility in groundwater is fundamental for many purposes related to As risk management. This includes the setup of process‐based geochemical models (e.g., Appelo & Postma, 2005; Gao et al, 2020; Jakobsen et al, 2018; Michael & Khan, 2016; Postma et al, 2007; Rathi et al, 2017; Rotiroti et al, 2014) predicting the spatial and temporal scales of occurrence of As concentrations in groundwater (e.g., predicting where As concentrations exceed the 10 μg/L recommended by World Health Organization [WHO]).…”

High-Arsenic Groundwater in Paleochannels of the Lower Yellow River, China: Distribution and Genesis Mechanisms

“…According to Figure 8, the As concentration shows a tendency of a significant increase as the HCO3proportion increases, which indicates that As release is related to high HCO3concentrations. A significant correlation between As and HCO3 -has been observed in groundwater of the Ganges plain [41], Hetao Basin [42], and Guide Basin [22]. Studies suggested that the HCO3 -ion can substitute arsenate from the surface sites of iron oxides, leading to arsenic mobilization [43][44][45].…”

Groundwater arsenic content in quaternary aquifers of the Red River delta, Vietnam, controlled by the hydrogeological processes

“…Natural contamination of groundwater by arsenic is a widespread problem in SE Asia ( van Geen et al, 2003 , Winkel et al, 2011 , Kocar et al, 2014 , Stahl et al, 2016 , Gao et al, 2020 ). Groundwater arsenic concentrations in the floodplains of SE Asia are the result of interacting hydrochemical, sedimentary and geological processes.…”

“…Groundwater arsenic concentrations in the floodplains of SE Asia are the result of interacting hydrochemical, sedimentary and geological processes. Arsenic is released to groundwater from iron hydroxides reduced by organic matter under anoxic conditions ( Postma et al, 2007 , Kocar et al, 2014 , Postma et al, 2016 , Gao et al, 2020 ). With time the reactivity of the organic matter in an aquifer decreases, and the rate of the reduction processes and the resulting groundwater arsenic content decreases ( Lawson et al, 2016 , Postma et al, 2016 , Jakobsen et al, 2018 ), also due to large water volumes recharged through the aquifer, leaching sorbed arsenic from the sediment ( Kocar et al, 2014 , Jakobsen et al, 2018 , Sø et al, 2018 ).…”