Major ion geochemistry of Ghannouch–Gabes coastline (at Southeast Tunisia, Mediterranean Sea): study of the impact of phosphogypsum discharges by geochemical modeling and statistical analysis

Abstract

Since the 1970s, the Ghannouch–Gabes coastline (Southeast of Tunisia, Mediterranean Sea) has experienced significant industrialization, especially after the chemical industries were set up for phosphate ore processing in Ghannouch. These industries are the source of various discharges, phosphogypsum (PG) in particular, which is directly discharged into the sea, disastrously impacting the marine environment. The present study utilized geochemical modeling (PHREEQC) and multivariate statistical tools to identify and analyze the natural and anthropogenic factors governing the chemical composition of the major elements of the Ghannouch–Gabes coastal waters, especially through the study of the impact of the compounds derived from the PG discharge. To achieve this, a geochemical modeling and statistical investigation was conducted by dividing the study area into two zones: I and II. Zone I was located in the south of the study area, between the wadi Gabes and wadi al Fard. In Zone I, the water was less influenced by the PG inflow. The concentrations of the major elements, temperature values, pH, and dissolved oxygen content were comparable with those of the average surface seawater. Zone I water was supersaturated in terms of calcite and undersaturated with respect to gypsum and fluorite. Zone II, located in the north of the study area, between wadi Ettine and wadi Gabes showed water that was strongly influenced by the release of PG, with important amounts of Ca2+, SO4 2−, and F−. Application of the PHREEQC program showed that the PG released in this area was almost completely dissolved, a process accelerated by the high acidity and the high temperature of the water in this zone.