LAUSR

Abstract Freshwater submarine groundwater discharge (SGD) frequently occurs in areas of karst coastline where karst aquifers are hydraulically connected to the sea. Though up to 25% of the world's coastline is karst, little work has been done to determine the ecological impacts of karst-channelled freshwater SGD. Reported herein are the effects of karst-channelled freshwater SGD on the rock pool sessile assemblage in the locale of Olhos de Agua on the south Portuguese coast. Two quadrat surveys were conducted in eight intertidal rock pools, which ranged in freshwater SGD content from 0 to 57.3%. Salinity and nitrogen (NO3− and NO2−) concentrations were measured in the eight surveyed rock pools, as well as a further three rock pools on the same plateau, three inland groundwater boreholes and the adjacent coastal marine environment. There was a strong negative correlation between salinity (used as a proxy for freshwater SGD) and nitrogen concentration (r2 = 0.98; p