Identification of the origins of vadose-zone salinity on an agricultural site in the Venice coastland by Ionic molar ratio analysis
E. Zancanaro, P. Teatini
Dept. of Civil, Environmental and Architectural Engineering,
University of Padova, Padova, Italy
E. Scudiero
Department of Environmental Sciences, University of California, Riverside, USA
F. Morari
Dept. of Agronomy, Food, Natural Resources, Animals and Environment, University of Padova, Legnaro, Italy
ABSTRACT
Saltwater contamination seriously affects water quality and land productivity of
reclaimed farmlands along the Venice Lagoon, Italy. To characterize the hydrogeochemical
dynamics involved in this phenomenon, a three-year study was carried out in an experimental field
located at the southern margin of the Venice Lagoon. Soil matric potential, quality of soil pore water
and groundwater, and soil physical and chemical properties were monitored at five monitoring
stations. Relationships between Cl-, Na+, Mg2+, Ca2+,
K+, SO42-, Br- ionic concentrations, and electrical
conductivity of the water samples with the soil characteristics (e.g., texture, exchangeable cations)
were investigated. Soil water flux direction was calculated and related to ion concentrations.
Moreover, specific molar ratios (Mg/Ca, Na/Cl, Cl/Br, and SO4/Cl) were calculated to identify the
main drivers affecting salinity in the field. The study confirmed that the experimental site was
strongly affected by soil and water salinity, and two major contamination dynamics were identified.
The first one was mainly driven by seawater intrusion from the near lagoon and salty watercourses,
while the second was derived by the interactions between the peaty soil and salts that were
originally in place, since the area was only reclaimed a few decades ago. The latter highlighted the
potentiality of the experimental field to become an acidic sulfate environment. Ionic ratios were
implemented and proved to be an important tool for the identification of salinity origin.
