A Critical Review of Groundwater Table Fluctuation: Formation, Effects on Multifields, and Contaminant Behaviors in a Soil and Aquifer System

Abstract

The groundwater table fluctuation (GTF) zone is an important medium for the hydrologic cycle between unsaturated soil and saturated aquifers, which accelerates the migration, transformation, and redistribution of contaminants and further poses a potential environmental risk to humans. In this review, we clarify the key processes in the generation of the GTF zone and examine its links with the variation of the hydrodynamic and hydrochemistry field, colloid mobilization, and contaminant migration and transformation. Driven by groundwater recharge and discharge, GTF regulates water flow and the movement of the capillary fringe, which further control the advection and dispersion of contaminants in soil and groundwater. In addition, the formation and variation of the reactive oxygen species (ROS) waterfall are impacted by GTF. The changing ROS components partially determine the characteristic transformation of solutes and the dynamic redistribution of the microbial population. GTF facilitates the migration and transformation of contaminants (such as nitrogen, heavy metals, non-aqueous phase liquids, and volatile organic compounds) through colloid mobilization, the co-migration effect, and variation of the hydrodynamic and hydrochemistry fields. In conclusion, this review illustrates the limitations of the current literature on GTF, and the significance of GTF zones in the underground environment is underscored by expounding on the future directions and prospects.

Critical Role of Mineral Fe(IV) Formation in Low Hydroxyl Radical Yields during Fe(II)-Bearing Clay Mineral Oxygenation

“…With respective to the role of Fe­(IV) in redox reactions, it has been well established that aqueous Fe­(IV) can serve as an good oxidant for the selective oxidation transformation of inorganic and organic contaminants [e.g., As­(III), PMSO, phenol, and sulfamethoxazole in technical systems. In contrast, the formation of mineral Fe­(IV) is usually overlooked in redox-fluctuating subsurface environments . In soils and aquifers, O 2 and H 2 O 2 can be transported periodically into anoxic environments, due to both natural processes (e.g., rainfall and surface water–groundwater interaction) or anthropogenic activities (e.g., irrigation and contamination remediation project) .…”

“…In contrast, the formation of mineral Fe­(IV) is usually overlooked in redox-fluctuating subsurface environments . In soils and aquifers, O 2 and H 2 O 2 can be transported periodically into anoxic environments, due to both natural processes (e.g., rainfall and surface water–groundwater interaction) or anthropogenic activities (e.g., irrigation and contamination remediation project) . In such cases, Fe­(II)-bearing minerals can be readily oxidized to produce abundant mineral Fe­(IV), with a production higher than • OH by up to 1 order of magnitude.…”

“…In recent years, the dark formation of • OH from reduced soil/sediment oxygenation has gained increasing recognition, serving as a sustainable • OH source in redox-fluctuating subsurface environments. − This novel pathway of • OH generation is via the activation of molecular oxygen (O 2 ) by reduced species [especially mineral Fe­(II)] in the subsurface, ,− distinguishing it from the photochemical generation of • OH in Earth’s surface environments including atmosphere, surface water, and ocean. − The dark formation of • OH from mineral Fe­(II) oxygenation plays an important role in the microbial activities, − the oxidative transformation of recalcitrant contaminants [e.g., As­(III) and trichloroethylene ] and the chemical pathway of the formation of greenhouse gas (e.g., CO 2 , CH 4 , and N 2 O) at oxic–anoxic interfaces − in redox-fluctuating environments . In soils and sediments, Fe­(II)-bearing clay minerals are typically recognized as the important contributors to O 2 activation and • OH production. , Given the global distribution of clay minerals, which host significant amounts of Fe­(II) , and constitute ∼21.5% of the Earth’s crust by mass, understanding the mechanisms of Fe­(II)-bearing clay mineral oxygenation is critical for gaining insights into the • OH-induced global cycling of elements and contaminants in the shallow subsurface …”

Migration and remediation of typical contaminants in soil and groundwater: A state of art review

“…Runoff and deposition are the two main pathways of HMs migration in soil and groundwater (Figure 1b) (Qiao et al, 2019). Some HMs enter the runoff through dissolution, while the other part is adsorbed on soil particles and then migrated through runoff (Qiao et al, 2023;Wei et al, 2024). There are many effects that can affect the migration of HMs in soil and groundwater, including the physical (particle size, water content, roughness) as well as chemical properties (pH, concentration) of the soil and groundwater (Ceballos et al, 2023;Feng et al, 2023;Qiao et al, 2023).…”

“…groundwater is influenced by the physiochemical properties of the surrounding environment (Wei et al, 2024). Additionally, these natural factors can independently or synergistically influence the migration of contaminants in the subsurface environment (Cortes-Arriagada et al, 2023;Grolimund & Borkovec, 2005;Jiang et al, 2023).…”