Geochemical assessment of surface sediments in Tabarka's coastal ecosystem: An integrative analysis of trace metals and nutrient loading

Abstract

In coastal Mediterranean regions the accumulation of contaminants in marine sediments is driven by the combined pressures of anthropogenic activities and environmental settings.This study investigates the influence of trace metals (TMs), total organic carbon (TOC), and nutrients, including total nitrogen (TN), from the El Kebir River on sediment quality in Tabarka's coastal ecosystem. In May 2024, we collected 24 surface sediment samples for geochemical and mineralogical analysis. The average concentrations of trace metals in the sediments were as follows: Fe (25,881 mg.kg⁻¹), Cu (9.45 mg.kg⁻¹), Zn (81.16 mg.kg⁻¹), Pb (35.70 mg.kg⁻¹), and Ni (44.45 mg.kg⁻¹). Average TOC content was 0.93 % while TN was only detected at riverine stations ranging from 0.3 % to 0.52 %. Pollution indices including the Pollution Load Index (PLI = 0.66), Contamination Factor (CF) for Pb = 1.78 (moderate contamination), Geoaccumulation Index (Igeo), and the ecological Risk Index (RI) = 10.14 (low ecological risk), indicated that the area can be classified from unpolluted to moderately polluted. The TN/TOC ratio suggests a mixed origin of terrestrial and marine organic matter where higher values (0.12 – 0.15) are likely due anthropogenic TN inputs. The Pearson correlation coefficient (r) analysis reveals good positive correlations (r > + 0.5) between trace metals and organic matter (TOC, TN), emphasizing the anthropogenic nature of this contamination. Principal component analysis (PCA) revealed two dominant sources of contamination linked to wastewater discharge and rainwater drainage. While results suggest moderate contamination level, continued accumulation of trace metals and nutrients could alter ecosystem functioning and exacerbate long-term ecological degradation.These findings emphasize the apparent need for urgent measures to improve wastewater treatment and pollution control to protect the coastal environment of Tabarka.