Abstract
Lagoon-barrier systems are a dynamic coastal environment. When an ephemeral connection between a lagoon and the ocean develops, it has significant impact on hydrology, sedimentology and ecology. Increasingly, human actions and sea level rise also influence lagoons with the potential to increase their connectivity with the ocean. The Muni-Pomadze lagoon in central Ghana is a small lagoon-barrier system that is intermittently open to the ocean. Following opening in 2014 the lagoon was open to the ocean for more than two years. Causes for the unusually long period of lagoon opening are unclear although human intrevention has played a role. Field observation, digital mapping and GIS analysis of the shoreline during the two year period of lagoon opening has enabled an understanding of how the lagoon-ocean connection has impacted coastal morphology, erosion and sedimentation. Opening has resulted in rapid changes to the location of the barrier breaching (tidal inlet), erosion on the barrier and sedimentation in the lagoon. Such modifications have implications for local resources and ecosystem services that underpin the livelihood and wellbeing of local communities. Elucidating how a connection to the ocean impacts lagoons and the coastal communities they support are important to managing lagoons not only in Ghana but across West Africa.
Highlights
Lagoon-barrier environments are estimated to occupy 13% of coastal areas worldwide (Duck and De Silva 2012) where they are found along tectonically-stable, low-lying coastlines
Reasons for the extended period of lagoon opening are uncertain it was facilitated by local people driving boats through the tidal inlet at low tide
The open connection between the lagoon and ocean resulted in increased sedimentation in the lagoon, narrowing of the lagoon barrier and shifts in the location of the tidal inlet and sites of erosion
Summary
Lagoon-barrier environments are estimated to occupy 13% of coastal areas worldwide (Duck and De Silva 2012) where they are found along tectonically-stable, low-lying coastlines. They are highly productive ecosystems that provide a wide range of natural functions (Flower and Thompson 2008). The lagoons and the barriers fronting them formed as sea levels rose at the start of the Holocene. As coastal populations have grown globally there is increasing potential for human intervention to modify lagoon systems and their ocean connectivity (Evans 2008). Human influence on lagoon opening may be direct or indirect.
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