Sedimentation and metal accumulation in the Gulf of Urabá – Colombian Caribbean: A 150-year record of natural processes and human impacts

Natural and human factors control the sediment accumulation rates and metal deposition in estuaries. This study analyzes the changes in sedimentation rates and metal accumulation in the Gulf of Urabá (southern Colombian Caribbean) over the last 150 years. The sedimentation rates of three cores (C1, C2, and C3) were determined using the constant flux (CF) model based on the ²¹⁰Pb isotope, averaging 0.14 cm/y, 0.22 cm/y and 0.10 cm/y, respectively. The temporal distribution of both major (Al, Fe, Ca, Mn) and minor (Zn, Cr, Cu, Ni) metals revealed important historical events, including the relocation of the main tributary mouth, intensive land use changes, and extreme climatic events. In agreement with previous studies in the area, moderate contamination and metal enrichment were found based on three geochemical indices (enrichment factor, anthropogenic factor and geo-accumulation index) considering global crust reference values. However, a lack of or minimal pollution was evident when considering the local background metal concentrations, which were determined in the bottom core sediments (2583 y BP). Therefore, this study evidences the relevance of using local background to determine metal pollution in surface sediments and cores. Despite high freshwater inputs and sediment supply, as well as anthropogenic activities in the gulf, sedimentation rates and metal accumulation are low compared to other marine environments worldwide, due to the presence of a salt wedge intrusion. The salt wedge creates a density difference, causing the clay fraction of the sediments, along with associated pollutants, to remain suspended for extended periods. As a result, sedimentation is hindered, and these materials are transported out of the gulf. Consequently, fine and medium silt dominate sedimentation and metal accumulation dynamics in the estuary.