EVALUATION OF TEMPORAL VARIATIONS IN SEDIMENT FLUX OF A TROPICAL ESTUARY

Sediment flux in estuaries can be influenced by natural and anthropogenic inputs, as such understanding its variation is vital for effective environmental management. The tropical Wouri Estuary in Cameroon receives water from three main rivers draining urban, industrial, and agricultural areas. The complex inputs into the estuary can significantly affect sediment flux that will consequently impact the estuary ecosystem.

In other to understand the variation in sediment flux in this estuary, a sediment core from a tidal flat in the estuary can be used as a proxy for time to reveal past conditions, pollutant levels, and ecological changes. We obtained a 78 cm sediment core from a tidal flat in the estuary and analyzed it at 5 cm intervals for organic content using Loss on Ignition (LOI) and for elemental concentration using X-ray Fluorescence (XRF).

The LOI results indicate organic content ranged from 1.0 to 3.0 wt.% between 0 and 35cm depth and increased from 3.0 to 13.5 wt.% from 35 to 75 cm depth. This variation in organic content correlates with lithological observations, where sediments transition from silty coarse material at the top to dark muddy sediments at the base. To understand elemental variation, we ratioed the concentrations of major and trace elements in the sediments to background values from the Upper-Continental Crust to determine the elemental enrichment factor (EF). The calculated EF values were used to assess variation in the concentration of elements within the sediment flux.

Sulfur generally decreases towards the surface, similar to organic matter, except at a depth of 50 cm where it shows an extremely high EF of 46. At 50 cm depth, where sulfur EF peaks and begins to decline, The EFs of Sb, Mo, Co, and As begin to increase in the sediment flux towards the surface. The EFs of Sb, Co, Mo, and As range from 4 to 27, 2 to 7, 3 to 7, and 6 to 7, respectively, denoting their significant enrichment from 50 cm depth to the surface in the sediment flux. The 50 cm depth from which the significant enrichment of these elements was observed is interpreted to be the time from which anthropogenic contributions in sediment flux became significant in the estuary. To determine the specific timeframe for the anthropogenic contributions, the sediment core sample will be subjected to geochronological dating in further studies.