Groundwater - lake interaction in a mediterranean coastal aquifer: the Alimini lake case study (Southern Italy)

The current study is focused on the characterisation of a coastal water system located in the Apulia Region, Southern Italy. The study site lies in the context of a semi-arid region, and comprises a freshwater lake fed by a multi-layer shallow porous aquifer. Groundwater is the main freshwater resource of the area, and suffers from an intensive exploitation that rises dramatically during summer, due to the increase of both population, caused by the massive presence of tourists, and the demand by agriculture. This study is intended to provide insight into the interactions between groundwater and lake water, in view of the potential lake water exploitation for drinking purposes, in order to help efficient and sustainable water management by local authorities. Four monitoring campaigns were carried out throughout one hydrological year to collect a set of water samples both from the lake and wells in its nearby surroundings. Geochemical interpretation of water quality data was performed by comparing a set of hydrochemical indicators that can suggest the processes controlling the chemical composition of groundwater, with special attention to the potential seawater intrusion. The applied indicators included a number of correlations involving major ions concentrations and a few physico-chemical parameters relating thereto, e.g., total dissolved solids, and seawater fraction. Groundwater and lake water quality were then compared, particularly considering the standard values for drinking water. Data processing was aimed at bringing out potential seasonal variations of groundwater quality, due to the increased withdrawal from wells in the summer season, and the consequent potential impact on lake water quality. Results suggested that groundwater chemistry was mainly controlled by the dissolution of carbonate minerals, with almost no contribution of cation exchange mechanisms, and a minimal impact of saltwater intrusion only into the wells closer to the coastline. The extent of intrusion showed no significant variation throughout the year. Lake water quality closely mirrored that of the feeding groundwater. Data analysis suggested that either biological and chemical processes occurring in the lake ecosystem, or anthropic activities in the area, did not have an impact on drinking water quality standards.