Coastal aquifers are a critically important water resource, which supports coastal populations and economies globally. Approximately half of the world’s population, including eight out of ten of the world’s largest cities, are located in coastal areas. Thus, good understanding and management of coastal aquifers constitute a critical component of global water security. Anthropogenic stressors including over-abstraction of groundwater, as well as climate and weather events (e.g. tsunami, king tide, sea-level rise, and drought), can cause saltwater intrusion (SWI) with profound impacts on water quality, quantity, and demand, which globally threatens coastal water security. Hundreds of millions of people could be directly affected by seawater intrusion. Thus, understanding coastal groundwater vulnerability is critical for economic, social, and environmental sustainability of coastal areas.

Geofluids in coastal aquifers are important reservoirs and pathways, which are directly controlled by the interactions between humans and the marine environment. Fluxes of geofluids from the land to the ocean, known as submarine groundwater discharge (SGD), deliver large loads of chemical compounds and dissolved ions to coastal estuaries and oceans. Circulation of marine water through these coastal aquifers alters the chemistry of both terrestrially-derived fluids and marine waters. Important impacts of SGD have been found on regional marine ecosystems and global oceanic chemical budgets. However, the magnitude and composition of SGD have been poorly described and quantified in many coastal systems because of the diffuse and heterogeneous nature of flow in coastal settings.

This special issue welcomes original research and review articles dedicated to covering a broad range of research activities, findings, and recent scientific advances in SWI and SGD, as well as field and laboratory methods and techniques that can be used to monitor and better understand the processes occurring in coastal aquifers.

Potential topics include but are not limited to the following:

• Controls on temporal and spatial distribution of SGD
• Impact of geological heterogeneity on SGD and SWI
• How chemical reactions in coastal aquifers affect waters of terrestrial and marine origin
• Projections of future water demand and groundwater supply in coastal areas including artificial and atoll islands
• Assessment of groundwater vulnerability from anthropogenic and climate stresses
• Engineering practices for aquifer salinization prevention
• Innovative uses for saline groundwater