Distribution and Environmental Risk Evaluation of Metals in Sediment Cores from Marmara Ereğlisi Shelf, Marmara Sea, Turkey

Abstract

This paper studies trace element contents in core sediments from Marmara Ereglisi on the northern shelf of the Marmara Sea. The main objective is to detect the concentrations of the selected elements (Al, As, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn) and historical evolution of sediment quality. The average concentrations of elements in mg/kg are 17,500 for Al, 5 for As, 70 for Cr, 12 for Cu, 10,742 for Fe, 137 for Mn, 44 for Ni, 20 for Pb, 43 for V and 44 for Zn. The average percentages of the sand, silt and clay fractions are 17%, 36% and 47%, respectively. Based on contamination factor, enrichment factor and pollution load index, computed from carbonate-free metal values, the core sediments are unpolluted for Al, Cr, Cu, Fe, Mn, Ni and V for the entire length of the cores and moderately polluted for As, Pb and Zn in the upper parts of the cores. The relative metal enrichment in cores starts at core depths of 13 to 39 cm depending on sedimentation rates, which commonly increase from the outer shelf toward the coast. Considering the sedimentation rates, the metal pollution on outer and inner shelf areas started about 400–500 years ago. Contamination of the northern shelf sediments is insignificant compared to those of the southern shelf, the semi-enclosed bays and gulf areas of the Marmara Sea with large catchment areas having a high population density and agricultural activities, as well as with similar marine shelf areas elsewhere in the world. This is mainly due to the small catchment area and the dynamic circulation system of the Marmara Ereglisi Shelf area.