The effect of heavy metals and physicochemical variables on benthic macroinvertebrate community structure in a tropical urban coastal lagoon

Benthic macroinvertebrates are key bioindicators of pollution and an important component of food chains on wetlands. Here, we investigated the effect of heavy metals and physicochemical variables on the benthic macroinvertebrates community structure in a tropical urban coastal lagoon in Ghana which is known for its importance in the support of migratory waterbirds. Sediment samples were collected from seven different sites in the lagoon and analyzed for heavy metals. The physicochemical characteristics of the overlying water, sediment organic matter and silt/clay content were determined at these sites. The benthic macroinvertebrates abundance, species richness and diversity at each of the sites were further determined. The results indicated low levels of Zn, Cr, Pb, Cu and Cd in the lagoon with chironomids being the dominant benthic macroinvertebrates. Overall, the benthic macroinvertebrates community structure was not affected by the levels of heavy metals as toxic units were less than one. The benthic macroinvertebrates community structure was generally influenced by the dissolved oxygen, temperature levels of the overlying water, silt/clay and organic matter in the sediment. Increased benthic macroinvertebrates abundance was associated with lower water temperatures and elevated levels of silt/clay and organic matter in the sediment.