INVESTIGATION OF WATER - SEDIMENTS INTERACTION IN ESTUARINE RIVERS

Characterizing water - sediments interactions in coastal locations may be key to understanding the evolution of anthropogenic signatures of pollution in coastal water systems. In June 2019, we collected water column and sediments samples from 30 locations associated with three rivers draining different rock terrains within the Wouri Estuary in Cameroon. Field measurements were conducted using a multi-parameter probe to record parameters such as dissolved oxygen, pH, conductivity, salinity, and temperature. Major ion concentrations in water, including nutrients such as nitrates, phosphates and ammonia were measured. Stable isotope compositions of the water samples, δD, δ¹⁸O, δ¹⁷O, were also analyzed. The riverbed sediments were analyzed by X-Ray Fluorescence to determine the concentrations of heavy metals.

Nutrient concentrations were determined to be within acceptable limits and were similar for the three river segments. The isotopic composition of water samples from the three rivers also shows similarities with mean concentration of -12.3 % ± 2.7, -3.2 % ± 0.6, -1.7 % ± 0.3 for δD, δ¹⁸O, δ¹⁷O, respectively. Dissolved silica concentration varied from 4.5 to 15.5 mg/L in all sampled location. These values are inconsistent with potential pollution from urban activities, the seaport, farming, artisanal mining, and other anthropogenic activities around the estuarine rivers. The relatively similar ionic concentrations in water samples from the three rivers are attributed to the dilution of any leachates from surrounding country due to heavy precipitation at the peak of the rainy season, June/July when samples were collected. Heavy metals from sediments were divided by background values of the Upper-Continental Crust, to determine their enrichment factor (EF). The mean EFs of Mo and As were 4.87 ± 4.33 and 6.73 ± 1.62, respectively. While Mo was significantly enriched for some locations, As was enriched in all samples. Correlation analysis did not show any relationship between the water and sediment chemistry. Further sampling in the estuary during the dry season is planned to investigate the seasonal effects on the estuarine water and sediment chemistry.