Elco Luijendijk , Tom Gleeson, Nils Moosdorf

The flow of fresh groundwater towards the world oceans may provide substantial inputs of nutrients and solutes to the oceans. Here we present a spatially resolved global model of coastal groundwater discharge to show that the contribution of fresh groundwater is lower than most previous estimates and accounts for only ~0.6% of the freshwater input and ~2% of the solute input to the oceans. However, the coastal discharge of fresh groundwater displays a high spatial variability and for an estimated 20% of the world’s estuaries, salt marshes and coral reefs the flux of terrestrial groundwater is high enough to pose a risk for pollution and eutrophication. Coastal groundwater discharge constitutes a diffuse and largely unmonitored source of nutrients which given the slow rates of groundwater flow may continue to pose a pollution risk for vulnerable coastal ecosystems long after sources of pollution have been addressed.