Multi-tracer assessment of seasonal water source changes in coastal water systems along the southeastern coast of Ivory Coast (West Africa)

Proper management of coastal freshwater resources depends on an understanding of processes controlling their chemistry and seasonal flowpaths. A quantitative approach involving the coupling of major solutes and isotopes (delta O-18, delta H-2) of 180 samples in end-member mixing analysis (EMMA) was adopted to elucidate seasonal patterns of hydraulic exchanges amongst coastal waters along the Ebrie Lagoon catchment, Ivory Coast. The results show that the Ebrie Lagoon is a hydrologically dynamic system. In the dry season, evaporation and seawater inflow are the dominating processes, while in the wet season, river discharge is the main water source in the lagoon. Regional geology plays a significant role in aquifer recharge patterns. The Quaternary aquifer responds faster to precipitation, while the Mio-Pliocene aquifer is recharged indirectly via floodplain seepages. Salinization of over 90% of wells arises from hydrological exchanges with the Ebrie Lagoon. A diluted seawater effect was recorded in wells during the wet season owing to the relative increase in freshwater inflow.