WATER QUALITY CHANGES NEAR THE MOUTH OF A RIVER DISCHARGING INTO THE TROPICAL WOURI ESTUARY, DOUALA CAMEROON

We conducted a longitudinal survey of the water quality of the Mungo River which discharges into the tropical Wouri Estuary, Douala, Cameroon. Understanding the chemistry of the Mungo provides essential insight into the chemical dynamics of the estuary and how the estuary affects the river mouth. Our objective was to document the physicochemical properties of the Mungo River which would allow us to assess the estuary’s impact on the river. Surface water samples and measurements were taken during high tide on July 11, 2023 (peak rainy season) at fourteen stations from the estuary into the meandering river for a total of 24 km. The pH, temperature, dissolved oxygen (DO), and salinity were taken in-situ and grab samples were taken for laboratory analyses. Our results showed that the salinity decreased steeply from the estuary to about 7 km into the river. The alkalinity and DO measurements showed trends similar to the salinity, which rapidly decreased to the 7 km point in the river. Beyond 7 km, the rivers salinity stayed nearly constant, whereas the alkalinity and DO increased in an undulating manner to the 24 km endpoint of the survey. The alkalinity and DO increases can be attributed to anthropogenic factors such as sand mining, agricultural activities (nitrogen and phosphorous influx from fertilizers), and human habitations. The location of the change in slope of salinity, alkalinity and DO decreases is interpreted to be the limit of the estuary’s saltwater influence on the river chemistry. Our results demonstrate that the physicochemical properties of the Mungo River are influenced downstream by both incoming saltwater from the estuary and upstream by anthropogenic effects. The location of the limit of saltwater influence on the river is expected to fluctuate during low tide or the dry season.