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Impacts of lagoon opening and implications for coastal management: case study from Muni-Pomadze lagoon, GhanaLagoon-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. TheMuni-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.
Shoreline change and sea level rise at the Muni-Pomadze coastal wetland (Ramsar site), GhanaLagoon-wetland systems are common along low-lying coastlines. They provide rich species habitats, multiple ecosystem services and socio-economic activities. They are particularly susceptible to the impacts of sea level rise (SLR), especially in less developed countries (LDCs) where economic and development constraints limit adaptation. The Muni-Pomadze lagoon is one of five coastal Ramsar sites in Ghana and one of many along the country’s coastline. It is an intermittently closed lagoon with extreme seasonal hydrological and physico-chemical variation. Field observation, digital mapping and GIS analysis of the shoreline has enabled an understanding of coastal change and SLR at the lagoon. From 1972 to 2014 the high water mark has shifted landwards with an average retreat rate of 0.22 m/year. Evidence of erosion and sediment washover indicate loss of and a shift landward of the sand barrier separating the lagoon from the ocean. Creation of an inundation map for a one-meter rise of sea level reveals fragementation and breaching of the barrier and an increasingly permanent connection to the ocean. A more open lagoon system stabilises hydrological and physico-chemical conditions, leading to increases in biodiversity and aquatic productivity. The lagoon currently has no consideration of SLR in its management plan. The results of this analysis and the limited development of the Muni-Pomadze lagoon support a no intervention approach to coastal management that allows SLR to transform the closed lagoon to an open estuary. A similar approach at comparable coastal wetland systems in Ghana and in other LDCs could prove an effective management option.