Impact of commercial salt production on wetland quality and waterbirds on coastal lagoons in Ghana

A comparative study conducted on two saline coastal wetlands that have been developed into saltpans and two others (referred to as 'non-saltpans'), that are also saline but have no saltpans, describes the quality of lagoon water, benthic macroinvertebrates and waterbird communities characterising these wetlands. The wetlands were sampled monthly from September 2005-April 2006. Except for turbidity, which was significantly higher in the non-saltpans, (p < 0.05), all other physico-chemical parameters studied were not significantly different between the two wetland types (p > 0.05). The waterbird communities of the saltpans and non-saltpans, characterised by 48 and 50 species respectively, scored a Sorenson Index value of 0.88, indicating a high similarity. The population density of benthic macroinvertebrates in the saltpans and the non-saltpans was statistically similar (p > 0.05) but the population densities of waterbirds feeding exclusively on benthic macroinvertebrates were significantly higher in the non-saltpans (p < 0.05). Although the shallow ponds created for salt production might be providing more suitable feeding habitats for fish-eating birds, the development of these ponds has also reduced the exploitable area available to the birds feeding exclusively on invertebrates, requiring them to depend largely on the non-saltpans. Birds feeding exclusively on fish had significantly higher population densities in the saltpans (p < 0.05) than in non-saltpans. This was attributed to reduced efficiency of piscivory, due to the high turbidity associated with the non-saltpans. Waterbirds feeding on a wide range of food types showed no significant differences in their population densities (p > 0.05) in the two wetland types.