Assessing the effects of climatic variables on soil and groundwater salinity in a low-lying agricultural field near the Venice Lagoon, Italy

Costal reclaimed farmlands are commonly threatened by saltwater intrusion and peat-driven salinity, resulting in low and unstable agricultural productions. Climatic variables have a great effect on soil moisture and salinity influencing crop production during the various growing seasons. For this reason, monitoring soil water and salinity dynamics in the root zone during the crop growing season is fundamental to conceive mitigation strategies (e.g., precision irrigation techniques). To this end, a monitoring network was installed in an agricultural field located at the southern margin of the Venice Lagoon. Three soil-stations were placed along the main sandy paleochannel crossing the farmland southwest to northeast (stations S1, S2, and S3), while stations S4 and S5 were placed in two silty-loamy areas with high peat content. Each station was equipped with three T4e tensiometers (UMS GmbH, Munchen, Germany) at 0.3, 0.5, and 0.7 m, four Teros 12 sensors (METER Group, Inc., Pullman, WA, USA) measuring volumetric water content, temperature, and electrical conductivity (EC_b) at 0.1, 0.3, 0.5, and 0.7 m. In addition, a 2 m deep piezometer was installed to monitor groundwater electrical conductivity (EC_w) and depth to the water table. Soil samples were collected on each monitoring location and analyzed for texture, bulk density (BD), soil organic carbon (SOC), electrical conductivity (EC 1:5), pH, and cation exchange capacity (CEC). Moreover, a weather station was installed in the experimental field to accurately monitor the local meteorological conditions during the 2019 and 2020 growing seasons. The soil monitoring dataset shows that EC_b increases with depth at all locations. Moreover, rainfall events higher than 10 mm/day caused an increase in the EC_b at all layers and stations. The monitoring stations inside the paleochannel showed lower EC_b if compared to station S4 and S5, probably due to the highest hydraulic conductivity and, consequently, the highest leaching capacity. S5 was characterized by the highest peat content and showed the highest salinity in both soil and groundwater. In general, soil EC_b and groundwater EC_w showed similar behavior in 2019 and 2020, except for S4 and S5 that were saltier in 2019. These preliminary analyses demonstrated a strong influence of rainfall events on salinity behavior and highlights how climatic variables, soil heterogeneity, and saltwater intrusion at depth play an important role in the complex salinity dynamics within the root zone.