MAPPING SALINIZATION IN THE COASTAL AQUIFER OF RAVENNA (ITALY)

The groundwater of the shallow coastal aquifer of Ravenna (Italy) is strongly contaminated by salt. The salinization has strongly increased in the last decades and it is threatening the ecosystems of the wetlands, the pine forests, and the dunes of the Park of the Po Delta (Antonellini et al. 2008, Antonellini and Mollema 2010). The coastal aquifer (Fig. 1) is a closed system and water recharge can only occur via infiltration of the rainfall and excess irrigation water in the dune areas and where sandy deposits are exposed at the surface. The limited rainfall, strong evaporation rate, sea level rise, and land subsidence have limited the amount of freshwater infiltrating into the aquifer (Mollema et al. 2012). The groundwater salinization is caused by two processes: (1) salt-water intrusion from the sea boundary, because of the strong hydraulic gradients landwards and (2) upwelling of Holocene brackish and salty water from the bottom of the aquifer where the water table is below sea level. The driver for both groundwater salinization processes is land subsidence and drainage. The physical law (Ghijben-Herzberg) clearly states that for each unit decrease in water table elevation with respect to sea level, there is a 30 times unit rise in the interface between salt-water and freshwater. In the low lying coastal plain of Ravenna, all human activities (agriculture, urbanization, etc.) are possible thanks to the drainage of the Land Reclamation Authority. The pumping machines of the land reclamation authority need to pump more water to sea in order to keep the land dry as land subsidence keeps raising the water table with respect to the topography. This drainage brings salt-water into the groundwater.