Wet deposition of major ions and trace elements in rural and coastal-urban sites in Monastir Region, Eastern Tunisia

摘要

Wet deposition in the Monastir region (Eastern Tunisia) was studied during the period from September 19th, 2013 to March 10th, 2014. Two types of rainy events (West to Northwest and East to Southeast) were recorded during the study period. The geochemical investigation of soluble (Cl-, NO3-, SO42-, Na+, K+, Ca2+ and Mg2+) and insoluble (Pb, Cu, Cd and Zn) phases of wet deposits at two selected rural-agricultural (S1) and coastal-urban (S2) sites showed a significant impact of the anthropogenic components attributed to metals (Pb, Cu, Cd and Zn) and to ions (NO3- and SO42-). It was associated to the simultaneous effect of urban activity (mainly traffic) at the coastal-urban site (S2) and the brick factories, the highway and the railroads' traffic at the rural-agricultural site (S1). The significant contributions of wet deposition, in terms of chlorine and sodium fluxes at the coastal-urban site (S2), could be attributed to the maritime influence. The importance of the Ca2+, Mg2+ and K+ fluxes in rural-agricultural site (S1) could be explained by the impact of both agricultural soils' resuspension and the activity of the clay quarries (generating dust) located not far from this site. It was demonstrated that measured "soluble and insoluble" concentrations were not evidently correlated to rain amounts. They varied from a rainy event to another and from one site to another. This is possibly due to the load period of the regional atmosphere in terms of particulate matter which was highly variable between two successive rains. It was also probably due to the effect of Saharan dust advection which was significantly pronounced in the spring wet deposition. Furthermore, one cannot exclude the airflow characteristics effect (especially during the convective clouds) and the nature of activities in each site.