Salt contamination of Apulian aquifers: spatial and time trend

Abstract

The quality of groundwater of Apulian carbonate aquifers is severely affected by salt contamination due to seawater intrusion. Due the scarcity of surface water resources, the characterization of groundwater quality degradation risks and of spatial and temporal trend of degradation are particularly important in the region. To pursue these results considering the risk of salt contamination due to seawater intrusion, a simple salinity threshold approach, based on the determination of a single value dividing fresh groundwater from seawater contaminated groundwater, is proposed for Apulian groundwater. The threshold can be considered equal to 0.5 g/l for the Apulian karstic and costal aquifers. The spatial trend of 0.5 g/l salinity contour line in the period 1981-2003 is characterized. Along the areas close to the Adriatic and Ionian shoreline groundwater saline contamination is resulted to be a long-standing phenomenon. Only the Murgia interior and a restricted strip in the middle of the Salentine Peninsula have not been contaminated so far. The salt contamination is also characterized considering 17 time series of monthly chloride concentration, a parameter which can highlight the seawater contamination effects. Data from 1968 to 2001 are considered and compared with rainfall and temperature time series. The increased saline contamination is closely related to droughty years and to the increasing discharge by wells. Before 1980, no significant concentration increase was reported in the majority of wells. The phenomenon became apparent in the late 80s after some dry years that result in a reduced recharge of aquifers and increased groundwater withdrawals. Time series of mean annual values of specific electrical conductivity are also discussed. It is confirmed the existence of areas considerable protected from the seawater intrusion, of areas exhibited in serious manner to the salt pollution and, finally, of an immense portion of territory in which the quality of the groundwater depends exclusively from our capacity to manage the water resources.