St Lucia – Africa’s Largest Coastal Lagoon - Quaternary history and effects of global change: Papers 1-3

Abstract

St Lucia, is a large coastal lagoon, which is very sensitive to changes in water level,volume and quantities of inflowing freshwater. It is therefore sensitive to the effects of global change that alter sea levels and rainfall. Earlier studies have shown that, during the Eemian, St Lucia was a marine environment. At that time global sea level was 3-4 m higher than that at the present. During the falling sea level leading up to the Last Glacial Maximum, St Lucia was above sea level and the climate was mainly dry. Studies of cores at Brodie’s Crossing showed that there were episodes with a wet climate at 23 000 years BP. During this period peat was deposited. Overlying this is wind-blown sand. Diatom studies indicate that this overlying sand was mainly redeposited Eemian marine sediments. Studies of the effects of future global change have focused on three ecosystems: the estuary itself, the Eastern Shores, and the Eastern Shores–lagoon interface (Brodie’s Crossing). For the estuary ecosystem the proportion of time in each salinity-state changes, and hence the amount of time that the various ecological states occur in the system will change. For the sand aquifer ecosystem of the Eastern Shores, the plants are very sensitive to the depth of the water table below the surface. Rising sea level and increased precipitation will raise the groundwater table, and as a response there will be an elevation of the vegetation zones. For both ecosystems the original ecological patterns will be retained, but with different spatial or temporal expressions. For the land-estuary interface, we anticipate that erosion over long time may modify important groundwater-fed refuges, and make the estuary ecosystem more vulnerable to periods of high salinity.