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.
Highlights
Seawater intrusion in coastal areas is threatening groundwater quality and farmland productivity worldwide [1]
[38] characterized the long-term evolution of groundwater piezometric levels in coastal confined aquifers of Venice, while the origin, extent, and dynamics of the salt contamination, and their relation with the natural and anthropogenic forcing factors was deepened by [7]. None of these studies focused on the unsaturated zone and on the hydrogeochemical dynamics involved in seawater-soil water-groundwater exchange interactions
Soil and water chemical characteristics confirmed that the study site was strongly affected by seawater intrusion, different dynamics were identified
Summary
Seawater intrusion in coastal areas is threatening groundwater quality and farmland productivity worldwide [1]. This phenomenon naturally occurs in coastal areas [2] but is intensified by anthropogenic activities such as groundwater pumping or land-use change [3]. In the low-lying area surrounding the southern Venice Lagoon, in northern Italy, saltwater intrusion is exacerbated by local phenomena and features, including land subsidence, which superposes to sea-level rise of the Adriatic Sea, the presence of sandy paleochannels, seawater encroachment into the river mouth, and presence of brine waters. More significant land subsidence affected the farmland at the southern margin of the Venice Lagoon. The tectonic structures locally allow deep brines to move upwards triggered by infiltrating freshwater and a high withdrawal rate [4,10]
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