ASSESSING THE PHYSICOCHEMICAL VARIATIONS OF THE TROPICAL WOURI ESTUARY, DOUALA CAMEROON

The hydrology of the Wouri estuary is supported by the Wouri River, Mungo River, and Dibamba River. These rivers are expected to influence the water chemistry of the estuary as they drain through different rocks and agro-industrial areas, thus supplying nutrients from geogenic and anthropogenic sources into the estuary. We conducted an axial survey of the physicochemical and stable isotope properties to assess the role of watershed geology, anthropogenic activities, and tidal mixing. The sampling traverse was designed to capture the maximum effects of tide-induced seawater-freshwater hydrologic mixing of the estuary. We sampled 18 stations along a 36 km transect at ~2 km intervals. Our results show that salinity decreased from 39 to 28 psu over 6 km from the mouth, and increased to 31 at ~8 km, beyond which salinity levels decreased to freshwater at the river mouth. The alkalinity decreased from 60 to 48 mg/L from the estuary mouth to the river mouth and was positively correlated with salinity which we suggest to be related to seawater-freshwater mixing. Seawater-freshwater mixing is supported by the stable water isotope results. Our results also show chemical perturbations in alkalinity and nitrates near the estuary mouth which is likely caused by the direct release of waste from ships waiting to unload cargo. We also observe a significant decrease in DO concentrations caused by the release of nutrients and pollutants from the seaport and cement company, within the industrial zone near the river mouth. We concluded that seawater-freshwater hydrologic mixing controls the distribution of geogenic solutes and that anthropogenic disturbance of the estuarine chemistry occurs near the river mouth and the estuary mouth.