Submarine Groundwater Discharge Along the Israeli Eastern Mediterranean Coast and in Inland Basins

Abstract

Submarine groundwater discharge (SGD) includes all water that discharges directly from the aquifer and coastal sediments to the sea. Fresh water SGD occurs mainly at the coastline, while saline SGD (circulated seawater) occurs up to the outer shelf or even upper slope. SGD affects both coastal aquifer water budgets and coastal seawater chemistry and quality, since it often carries with it solutes and contaminants. In Israel, it mainly occurs from the Mt. Carmel coast northward, where the Cretaceous carbonate aquifer is either in direct contact with the sea or exposed nearby. It was shown that at the southern Carmel coast (Dor Bay), fresh water discharge is on the order of >1 x 106 m3 yr−1, which if applied to the whole Carmel coast is more than is withdrawn from the local aquifer. Fresh groundwater discharge to the whole Mediterranean is about 20% of the riverine discharge. However, when total SGD is considered (by Ra isotope mass balance), it sums up to 200–4, 300 x 109 m3 yr−1, which is much higher than riverine discharge and is probably mainly due to offshore discharge across shelves and shallow seas. It was shown both at the local scale (Dor Bay) and for the whole Mediterranean that SGD is a major conveyor of nutrients to the Mediterranean, although some of the nitrates are denitrified in the sediments (‘subterranean estuary‘) en route to the sea.