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Submarine groundwater discharge (SGD)

Luís Felipe Niencheski
Instituto de Oceanografia
Universidade Federal do Rio Grande
260 Marine Science Bldg

Submarine groundwater discharge (SGD) is a process defined as any and all input of water into a surface water body through the sediment - water interface, independent of the driving force, and the fluid source and composition.

Historically, the report of the existence of SGD dates back many centuries, when a submarine spring 2.5 miles offshore from Latakia, Syria, in the Mediterranean Sea was described. Other historical records focus on the collection of drinking water by Bahrain traders in offshore submarine springs in the Persian Gulf and by Etruscan people along the Black sea. Scientifically, however, the discharge of groundwater was ignored for many years, because it is considered as a process of difficult access and biogeochemically insignificant.

Today, it is known that although it is not visually as obvious as the discharge of surface water (ie, effected by rivers and lagoons), the groundwater discharge can occur directly into the sea wherever there is a connection between the marine an aquifer limits. These subterranean formations, which reserve large amounts of water, can extend over considerable distances from the coast, forming discharge points in the ocean.

Thus, the persistent and spatially diffuse character of SGD in addition to the high concentration of dissolved elements in the advecting fluid, make this process biogeochemically important, as it has been demonstrated in the last two decades for many diverse places in the world. For this study, which considers the advances of the studies of SGD in the Atlantic side of South America, we highlight that the first studies registered happened in the coast of São Paulo in 2003. Soon after, several studies were developed in the South of Brazil, Rio de Janeiro, Bahia and Pernambuco. In all of them, it was indicated that SGD supports a large fraction of the coastal primary production. In Argentina, SGD studies began in 2011 on the Patagonian coast, and, in 2016, the first SGD results were produced for the Uruguayan coast. All these studies show that although this Atlantic region receives an immense contribution of superficial water, as by the Amazon and La Plata rivers, the SGD studies present groundwater as a new source, and also a great exporter of macro and micronutrients for the coastal region, shelf off and to the open ocean as well.

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