Abstract
To determine nutrient fluxes derived from submarine groundwater discharge (SGD), we conducted monthly hydrological surveys on the coast of Jeju, a volcanic island located in the southern sea of Korea. The concentrations of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved silicon (DSi) were significantly correlated with salinity, indicating that fresh SGD (FSGD) is a major nutrient source in Jeju Island where no other coastal freshwater origins exist. Based on a DSi-mass balance model, seepage rate of FSGD was found to depend on 5-day precipitation before sampling campaigns, which immediately permeatedviaporous aquifers. Thus, the FSGD-driven nutrient fluxes were generally higher in rainy season (July–August) and September 2019 when typhoons occurred. However, high DIN and DIP fluxes were found during spring (March–May), even at low seepage rate, perhaps by a fertilizer input from agriculture activity. This study highlights that large variation of the SGD-driven nutrient fluxes was caused by environmental and anthropogenic factors and emphasizes on the importance of long-term investigation.
Highlights
Submarine groundwater discharge (SGD) is the outflow of groundwater from seabed to ocean regardless of water composition or driving force (Burnett et al, 2003)
Because Jeju Island is located on the pathway of a branch of the oligotrophic Kuroshio Current with very depleted nutrients and the submarine groundwater discharge (SGD) is a dominant source of terrestrial substances, this island is an ideal place to determine the influence of SGD-driven inorganic nutrients in the coastal ocean
The concentrations of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved silicon (DSi) were significantly correlated with salinity, indicating that the fresh SGD (FSGD) is a dominant source of nutrients in the bay, where no other freshwater origins exist
Summary
Submarine groundwater discharge (SGD) is the outflow of groundwater from seabed to ocean regardless of water composition or driving force (Burnett et al, 2003). Seawater can infiltrate into coastal seabed and discharge again, to the ocean as groundwater with various ranges of salinity. This is designated as saline SGD (SSGD). The water flux of SGD into the ocean was estimated to be similar or sometimes significantly larger than the river that acted as the major source of water. Kwon et al (2014) estimated the SGD flux to be 3–4 times larger than the rivers in the global oceans In the Atlantic Ocean, the water flux of SGD was 80–160% of the river (Moore et al, 2008). Kwon et al (2014) estimated the SGD flux to be 3–4 times larger than the rivers in the global oceans
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