Submarine Groundwater Discharge: Impacts on Coastal Ecosystem by Hidden Water and Dissolved Materials

Submarine groundwater discharge (SGD) is an underground pathway of exchange of water and dissolved materials between the land and ocean. The number of studies on SGD started growing at the break of the 21^st century, and many hydrological and oceanographic processes have been identified and characterized, such as tidal effects on SGD, water and solute fluxes and transformations through the subterranean estuary, and geochemical transports by SGD from land to the ocean. Despite great progress in methodologies and local assessment of SGD published in the past two decades, there still remain many unknowns such as the impacts of SGD on coastal ecosystems, including fisheries and coral reefs, there are gaps in large scale and global assessment of SGD, the evaluation of differences between different types of SGD and pore water exchange are not yet explored, and so on. SGD research is also important for groundwater resource management, because SGD and saltwater intrusion is a face and tail of the coin.

In this Research Topic, we collect state-of-the-art SGD studies including but not limited to field studies in bay, coastal, or basin scales, methodologies of assessment of SGD and its fresh and saline components, numerical simulations on SGD, evaluations of SGD on coastal ecosystems, and global assessment of SGD.

Coastal aquifers will be greatly affected by sea-level rise, changes in precipitation and land-use patterns, and increased groundwater withdrawal from aquifers. These effects will be reflected in changes in the magnitude and composition of SGD as well as the biogeochemistry of the subterranean estuary. Because of the importance of SGD on coastal geochemical budgets it is now timely to explore current and future expected SGD patterns and their effect on coastal biogeochemistry.