Master's Theses

Department

Geosciences

Degree Name

Master of Science (MS)

Abstract

Sediment flux in estuaries is influenced by both natural processes and anthropogenic activities. Understanding the historical and current trends in sediment flux inputs and geochemical composition are essential for evaluating the estuary’s response to natural and human-induced changes and for developing effective environmental management strategies. The tropical Wouri Estuary in Cameroon receives water and sediment inputs from three main rivers draining urban, industrial, and agricultural areas, as well as different rock terrains. The complex inputs into the estuary can significantly affect sediment flux, consequently impacting the ecosystem. Thereby making an understanding of the temporal variations in sediment inputs in the estuary crucial. In this study, a 78 cm sediment core from the tidal flat of the Wouri Estuary was sampled at 5 cm intervals for qualitative grain size and color variation. The Loss on Ignition (LOI) technique was used to analyze organic matter content, and elemental composition was determined using wavelength-dispersive X-ray fluorescence (WDXRF) spectroscopy. Lithological analysis revealed a transition from coarse sediment at the top to medium-fine sediment at the middle section and very fine sediments at depth, coinciding with a progressive increase in organic matter content from surface to depth. The lithological and organic matter content variations were interpreted to reflect changes in depositional energy, changing from low at depth to very high at the surface. Elemental concentrations of major and trace elements in the sediments were ratioed to their average Upper-Continental Crust abundance to determine the elemental Enrichment Factor (EF). Enrichment Factor analysis revealed consistent enrichment of As, Co, Sb, S, and Mo throughout the core, whereas Zn and U enrichment were confined to the surface and middle section, and Pb iv exhibited elevated levels near the surface despite not being generally enriched. Analysis of cross plots of the enriched elements and statistical analyses of correlation matrices, and principal component analysis indicated variations in the covariances of enriched elements at depth (20 – 78 cm) and at the surface (0 – 20 cm). Based on the marked abrupt and consistent changes in the covariation of the enriched elements, geogenic sources are attributed to enrichment at depth, while anthropogenic sources are suggested to dominate enrichment at the surface. Furthermore, the unique covariation of enriched elements towards the surface suggested two distinct sources of anthropogenic input. Anthropogenic activities such as metal smelting, port operations, and agricultural activities are suggested as the primary drivers for the concurrent enrichment of As and Co. Automobile emissions, coal combustions activities and lubricant waste are interpreted to be the likely sources of the simultaneous enrichment of Zn, Mo, and Sb. These findings underscore the dual role of natural and human-induced factors in shaping sediment flux and pollutant dynamics in estuarine systems.

Keywords

Wouri Estuary, Tidal Flats, Sediment Flux, Sediment Core, Enrichment Factor

Advisor

Dr. Henry Agbogun

Date of Award

Spring 2025

Document Type

Thesis

Rights

© The Author

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