Intertidal and submarine groundwater discharge on the west coast of Ireland

Submarine Groundwater Discharge is now a phenomenon of global interest, as studies show that it represents both a significant proportion of the fresh water input to the ocean, and a significant contribution to the loads of many substances. At present, little monitoring of groundwater in Ireland is carried out at its point of entry to seawater, and consequently the volumes of fresh water, and the loads of nutrients and contaminants being carried into Irish coastal waters by submarine and intertidal groundwater discharge (SiGD), are unknown. SiGD is the principal source of fresh water entering Irish coastal waters between the major west coast estuaries of the Corrib and the Shannon. Calculations of the volume of submarine SiGD delivered to southern Galway bay in winter indicate it equals 10–25% of the discharge of the R. Corrib, and that its nutrient load may be of the same order of magnitude as that from the R. Corrib. This coastal karst area includes important commercial shellfish waters, which may be strongly impacted by SiGD.

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► SiGD from a coastal karst area on the west coast of Ireland measured for the first time.
► SiGD volumes in winter equal 10–25% of the R. Corrib discharge to Galway Bay.
► SiGD may deliver similar loads of TON to Galway Bay as those from the R. Corrib due to high concentrations of TON in SiGD.