Characterisation of water quality in the island of Zakynthos, Ionian Sea, Western Greece

Abstract

This paper summarises the hydrochemical characteristics of the main aquifers of the island of Zakynthos, in the Ionian Sea. A total of 677 groundwater samples were collected from 139 points between 2004 and 2008. The karstic limestone of the mount Vrachionas in the west comprises the major drinking water supply of the island. Increased water demand resulted in the overexploitation and the encroachment of saline water intrusion to the north and south of Vrachionas. Chloride concentrations exceed drinking water threshold in 40% of the samples. Simple groundwater-seawater mixing is the main process occurring within the limestone aquifer. In the east, the confined multilayered Neogene aquifer comprises the secondary drinking water supply of the island. Saline intrusion in this area is limited due to geological constraints and the water is of good quality. Groundwater is clustered in 4 different groups depending on the prevailing hydrochemical process. The alluvial deposits in the central part of the island comprise a shallow localised aquifer pumped mainly for irrigation. This minor aquifer provides good quality irrigation water with some exceedances in chloride and sulphide. Groundwater in this aquifer is a result of simple mixing between fresh and sea water. Trace elements were also analysed resulting in values within the drinking limits.