Seawater–Groundwater Interaction Governs Trace Metal Zonation in a Coastal Sandy Aquifer

Abstract

Trace metals in the groundwater of coastal sandy aquifers significantly influence the coastal ecosystem, yet the spatiotemporal controls of these metals remain unclear. In this paper, we comprehensively revealed the distribution patterns, key controlling factors, potential ecological risks, and fluxes to the ocean of groundwater trace metals (As, Ba, Cr, Cd, Fe, Mn, Pb, and Zn) in a coastal deep sandy aquifer. The results showed a clear zonation of trace metals in the groundwater in relation to the mixing extent between seawater and terrestrial freshwater. The freshwater zone exhibited a relatively low concentration of trace metals, whereas the freshwater‐seawater transition zone showed a substantial quantity of dissolved Fe, Mn, As, and Ba. Seawater‐groundwater interactions significantly affected the Fe, Mn, As, and Ba concentrations through redox potential and pH gradients. The tide‐driven saline water zone was vulnerable to oceanic environments and anthropogenic activities, resulting in the enrichment of trace metals such as Zn and Cd. Driven by recirculated submarine groundwater discharge (SGD), the concentrations of trace metals in the density‐driven saline circulation zone were found to be higher than those in the surrounding areas. The ecological risk index suggested that the freshwater‐seawater transition zone posted the highest ecological risks. Trace metal fluxes (i.e., Fe, Mn, and As) via SGD significantly contributed to the total input into the sea, which may have potential impacts on the coastal environments. Our study highlighted the importance of seawater‐groundwater interactions on trace element cycling in coastal sandy aquifers.This article is protected by copyright. All rights reserved.

Salinity-Induced Changes in Heavy Metal Behavior and Mobility in Semi-Arid Coastal Aquifers: A Comprehensive Review

“…However, numerous studies observed that elevated concentrations of heavy metals, even in minor quantities, precede the natural accumulation of heavy metals in plant tissues, affecting their metabolism and functional means [55]. Elevated concentration of Pb can cause abrupt brain development [56], Cd could cause acute and chronic diseases [57], and Cu is used in the treatment of anemia, bone weakness, and cardiovascular issues [47] at elevated concentrations.…”

“…An interplay between evaporation, tides, waves, and precipitation could potentially cause highly intricate driving mechanisms, which significantly influence the subsurface flow patterns and transport of solutes or contaminants [37,46]. Numerous studies have concluded that seawater intrusion has major control over the concentration of contaminants in aquifers [47][48][49][50].…”

Impact of connected conduit on pumping-induced seawater intrusion in a coastal karst aquifer

“…In coastal regions, interactions of seawater and freshwater bring about unique groundwater environment, numerous endeavors have investigated chemical releasing and accumulations, biological environmental problems, and different coastal carbon budgets (e.g. Luo et al, 2022;Xiao et al, 2022;Zhang et al, 2022;Wang et al, 2023). Furthermore, in coastal karst aquifers, the seawater-freshwater interactions may be amplified since the existence of interconnected conduit systems (Arthur et al, 2007;Fleury et al, 2007).…”