Metal Contamination of Surface Sediments in an Urban Wetland: The Case of the Urban Natural Reserve of Pikine Grand Niaye and Dependencies (UNRPGND), Senegal
This study assessed the concentrations of cadmium (Cd), lead (Pb), and mercury (Hg) in surface sediments from seven lakes within the Urban Natural Reserve of Pikine Grande Niaye and Dependencies, using atomic absorption spectrometry. Cd concentrations ranged from 6.17 to 8.34 mg/kg, showing relatively uniform levels across the lakes. In contrast, Pb exhibited greater variability, with concentrations between ranging from 0.76 to 4.18 mg/kg, while Hg concentrations ranged from 2.15 to 3.72 mg/kg. Although spatial variations in metal concentrations were observed, the Kruskal-Wallis test revealed no statistically significant differences among the lakes. Seasonal variations were more pronounced. Cd concentrations were significantly higher during the wet season compared to the dry season. Pb levels also peaked in the wet season, with the highest values recorded at Lac Kakhira. Hg concentrations remained low during the dry season but increased notably in the wet season, particularly at Lac Maristes 1. The Kruskal-Wallis test confirmed significant seasonal differences for both Cd and Pb, while Hg concentrations did not show significant seasonal variation but not for Hg. The contamination factor indicated high contamination levels by for Cd and Hg, especially at Lakes Lac Maristes 1 and Lac Maristes 2, whereas Pb contamination remained low across all sites. The geo-accumulation index confirmed significant contamination by Cd but not by Pb, suggesting that Pb currently poses a limited threat to the reserve’s ecosystem. These findings underscore the urgent need for continuous environmental monitoring and the implementation of proactive management strategies to safeguard this vulnerable urban wetland.
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