The Venice coastal plain and its surroundings is suffering of soil and surface water salinization due to seepage of saline groundwater into drainage canals of agricultural lands and soil salinization due to irrigation water quality. To study this phenomenon, two agricultural fields experiencing crop yield decrease in the last years were selected. The fields are located in a reclaimed area at approximately 2 m below sea level in the Venice province, 2.5 km from the Venice Lagoon (Site 1) and in Rovigo province, 10.5 km from the Venice Lagoon and 18.5 km from the Adriatic Sea (Site 2). To delineate the salinity gradients, 9 high resolution vertical profiles of soil cores were collected with an electrical auger corer and analysed in the field via a Meter® TDR for porewater salinity, volumetric water content (VWC), and temperature, and in the laboratory for sedimentary organic matter (SOM) gravimetrically, major ions and trace elements (TEs) via IC and ICP-EOS, respectively. The composition of porewater’s leaching fraction (LF) was gained via deionized water batch extraction with solid liquid ratio 1:5, while the plant available water (PAW) was obtained via microwave hot water extraction in three selected profiles. Stratigraphical cores were almost homogeneous with the most permeable layers constituted by organic sandy layers. An average porewater salinity of 2.2 g/l with an upward increasing trend was found in Site 1, while an average porewater salinity of 3.5 g/l with a downward increasing trend was found in Site 2. Vertical profiling highlighted the strong connection among some trace elements and the saline organic horizons in Site 2, characterized by paleo-seawater upward fluxes. Conversely, Site 1 was mostly affected by evapoconcentration processes of irrigation waters. The PAW salinity was up to two times the LF, highlighting that organic layers are the major saline source in these reclaimed lands and they can release large amount of solutes as well as TEs.