Reply on RC1

Abstract

Eight sediment cores from the coastal marine area of West Saronikos Gulf have been analyzed for their grain size and geochemistry. The concentrations of eight metals (Al, Fe, Mn, Cu, Cr, Ni, Pb and Zn) along with total organic carbon (TOC) and carbonate content were measured. In cores taken at the deeper stations (above 100 m) the analyses were performed only in the prevailing fine fraction (f < 63 μm) while in cores from shallow stations (below 100 m) the analyses were performed separately in both fractions fine and coarse (63 μm < f < 1 mm). The cores are fairly homogeneous, in terms of carbonates and the down-core variability of % TOC, is characterized by high surficial values that decrease with depth. Metals from both geological origin (Al, Mn, Cr, Ni) and anthropogenic origin (Cu, Pb, Zn), are higher at the silt and clay fraction of sediments than the sand fraction. The spatial distribution of Al, Fe, Mn, Cu, Pb and Zn in surface sediments presents increasing concentrations from the northeast to the southwest part of the study area, from the shallow to the deeper parts in contrast to Cr and Ni which are increased in the northern nearshore stations. Based on the vertical distributions, the metal to Al ratios of Cu, Pb and Zn show a constant decrease over depth along most cores, indicating the anthropogenic effects to surface sediments, while Fe/Al is constant. Spearman’s correlation analysis performed among the fine grain metal contents, demonstrated a strong positive correlation (r > 0.5, p < 0.05) between Fe, Mn, Cu and Cu, Pb, Zn. Moreover, increased enrichment factors were determined at the fine fraction (f < 63 μm) of some sediments. The concentrations of Cr at most surface sediments are higher than the ERL (Effects Range Low) value (81 mg Kg-1) but below the ERM value (370 mg Kg-1) and the concentrations of Ni are higher than the ERM (Effects Range Median) value (51.6 mg Kg-1). Moreover, the concentrations of Cu, Pb, Zn, at most surface sediments, are below ERL values. The mean effects range medium quotients (mERMq) of surface sediments, based on the overall metal concentrations indicated that the surface sediments of most cores, are moderately toxic. The levels of Cr, Ni, Mn and Zn at most stations are decreased in 2017, but the concentrations of Pb and Cu are increased in 2017, compared to a previous study of 2007. The concentrations of Cu, Pb and Zn in the surface sediments of West Saronikos Gulf are lower than levels reported for Inner Saronikos Gulf and Elefsis Gulf, owing to the smaller industrial zone at the western coast, compared to the numerous polluting activities at the east coast of Saronikos.