B017-0002
Assessing Salinization and Pollution of Coastal Groundwater by Tidal Action: The Tropical Wouri Estuary, Douala, Cameroon

Tuesday, 8 December 2020
Poster
Goabaone Jaqueline Ramatlapeng, University of Delaware, Earth sciences, Newark, DE, United States, Eliot A Atekwana, University of Delaware, Department of Earth Sciences, Newark, DE, United States, Hendratta Ali, Fort Hays State University, Department of Geosciences, Hays, KS, United States, Isaac Knofor, University of Yaounde 1, Department of Earth Sciences, Yaounde, Cameroon and Nkoue Ndondo, University of Douala, Department of Geosciences, Douala, Cameroon
Abstract:
While numerous studies have revealed that salinization and pollution are the major processes that cause groundwater quality deterioration in coastal aquifers, relatively few studies have assessed salinization and pollution of coastal groundwater by estuarine water. In this study, we investigated the origin of salinity and pollution in shallow groundwater adjacent to the Wouri Estuary in Douala, Cameroon. We aim to ascertain if water from the estuary is the cause of salinization and metal and nutrient pollution of coastal groundwater. We conducted a time series investigation of water level, salinity and temperature at minute intervals for 67 h and assessed stable isotopes (δ¹⁸O and δD), major cations (Ca²⁺and Mg²⁺), iron (Fe) and nutrients (NO3-, PO42- and NH4+) in groundwater and in estuarine water in an adjacent tidal creek. The time-series groundwater level mimicked water level changes in the estuary. However, the temporal salinity and temperature in groundwater did not correspond to that of estuarine water, indicating that estuarine water did not intrude groundwater. The δ¹⁸O and δD of the groundwater and estuarine samples are collinear and fall along the local meteoric water line of Douala. Additionally, the salinity-δ¹⁸O relationship showed that the origin of salinity in coastal groundwater in the Douala coastal aquifer is not from seawater intrusion. The Mg²⁺/Ca²⁺ of <1 in groundwater compared to 6-8 in estuarine water support the non-seawater origin of salinity. We suggest an aquifer source for Fe and an anthropogenic pollution source for the nutrients (NO3-, PO42- and NH4+) in groundwater samples that had higher nutrient concentrations compared to estuarine water. We conclude that the salinity and quality of coastal groundwater in Douala is not affected by tide-induced salinization from the adjacent Wouri Estuary, but by geogenic sources in the aquifer and by anthropogenic activities.
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