THE TEMPORAL VARIATIONS OF HYDROGEOCHEMISTRY OF A TIDAL MANGROVE CREEK IN THE WOURI ESTUARY, CAMEROON

We conducted a time series analysis of water level, salinity, dissolved oxygen (DO), pH and alkalinity in a tidal creek between coastline and mangroves. Our aim was to determine the sources of water and their role in changing temporal chemistry of water in the tidal creek. We sampled at a single location about 6 km from the open estuary at varied intervals of 15, 30 and 60 minutes over semi-diurnal mixed tides. During rising tides, the salinity, pH and alkalinity decreased, while DO increased, and these signatures are reversed during falling tides. The low salinity during high tide can be explained by the estuarine water pushing back the freshwater from the River Wouri, resulting in hydraulic block that forces river water into the tidal creek. The increasing salinity, pH and alkalinity during falling tide results either from sub-marine groundwater discharge (SMGD) or drainage of mixed saline water from mangrove platforms. Our results can be used to suggest that in addition to fresh river water and saline seawater, there is additional input of saline groundwater and perhaps saline water from the mangrove platforms into the tidal creek. Our results further show that river water dominated the hydrology and solute behavior during rising tides, while SMGD and drainage from the mangrove platforms dominated the hydrology and solute behavior of the tidal creek during falling tides. The dominance of the different water sources and their hydrologic and chemical control of the tidal creek water illustrates the rapidly changing hydrodynamics of tidal creeks at the interface between land and mangroves.