Effect of Transient Wave Forcing on the Behavior of Arsenic in a Nearshore Aquifer

Abstract

Groundwater–coastal water interactions influence the fate of inorganic chemicals in nearshore aquifers and their flux to receiving coastal waters. This study evaluates the impact of variable wave conditions on the geochemical changes and distribution of mobile arsenic (As) in a nearshore aquifer. Field measurements in a sandy nearshore aquifer on Lake Erie, Canada, are presented with geochemical changes analyzed over a period of high waves. A numerical model of wave-induced groundwater flow dynamics, validated against field data, is used to provide insight into the physical flow processes underlying the observed geochemical changes. Rapid changes in dissolved As, Fe, Mn, and S demonstrate the importance of reactions as well as dynamic transport in controlling the behavior of reactive species, especially those that are redox sensitive. Field data suggest the presence of sediment traps, which under certain hydrological and geochemical conditions may result in a “hot moment” with episodic release of As. The study provides new insight into factors controlling the fate of reactive species in dynamic coastal environments as required to better predict chemical fluxes to coastal waters. Additionally, it highlights the need to pay particular attention to “hot moments” for reaction and transport caused by storms and waves.

Groundwater Flow and Moisture Dynamics in the Swash Zone: Effects of Heterogeneous Hydraulic Conductivity and Capillarity

“…For example, Xin et al (2010) developed a phase‐averaged approach where wave effects were represented by a wave‐induced onshore hydraulic gradient above the mean sea level, referred to as wave setup. This approach has been used in numerous wave relevant studies (Anwar et al, 2014; Malott et al, 2017; Rakhimbekova et al, 2018; Robinson et al, 2014). Geng and Boufadel (2015) developed a “net inflow” approach to upscale wave effects on subsurface flow and transport processes.…”

“…Previous studies have revealed that complex groundwater mixing occurs in the swash zone due to high‐frequency inundation and seawater infiltration by individual waves (Cartwright et al, 2002; Geng et al, 2014, 2017; Geng & Boufadel, 2015; Heiss et al, 2014; Malott et al, 2017; Xin et al, 2010). Swash and tidal action are a primary control on nearshore biogeochemical processes and submarine discharge of various chemical species (e.g., nutrients, carbon, arsenic, and trace elements) into coastal waters (Boehm et al, 2006; Brown & Boehm, 2016; Kim et al, 2017; Lässig, 2019; Mohapatra et al, 2011; Praveena et al, 2012; Rakhimbekova et al, 2018; Waska, 2019). Kim et al (2020) revealed that intertidal groundwater‐seawater mixing driven by tides likely creates a dynamic reactive circulation cell, where areas with high denitrification rates shift landward and seaward along the mixing zone though spring‐neap cycles.…”

A State-Of-The-Art Perspective on the Characterization of Subterranean Estuaries at the Regional Scale

“…More generally, hot moments in STE can be created through movements of the salinity gradient, when, e.g., phosphorus can desorb from aquifer sediment with increasing salinity and cause a spike of P fluxes to the ocean that is not directly connected to terrestrial or marine inputs (Flower et al, 2017). Hot moments can also result from shifts in groundwater flow paths due to changed wave activity, which have been hypothesized to trigger pulses of arsenic transport into coastal waters due to instability of iron oxyhydroxides under changing redox conditions (Rakhimbekova et al, 2018). Water residence time is an essential factor influencing chemical reaction kinetics in the STE.…”

Evaluating lacustrine groundwater discharge to a large glacial lake using regional scale radon‐222 surveys and groundwater modelling

“…To address lake water quality impairment, there is increasing need to identify, quantify, and manage all the sources and pathways delivering pollutants to lakes. While often overlooked, groundwater discharge can be an important delivery pathway for lakes (Knights et al, 2017; Lewandowski et al, 2015; Meinikmann et al, 2015; Rakhimbekova et al, 2018; Rakhimbekova et al, 2021; Rosenberry et al, 1999). Groundwater can enter a lake either directly from an aquifer, termed lacustrine groundwater discharge (LGD), or indirectly through groundwater‐fed streams that flow into the lake (termed indirect groundwater discharge) (Grannemann et al, 2000).…”