Assessment of metal pollution in sediment and its impact on the macrobenthic community of Richards Bay Harbour, South Africa

Port and industrial activities often cause contamination of estuarine sediments, yet information on sediment metal contamination in Richards Bay Harbour is limited. This study examined the extent and ecological relevance of metal contamination using sediment quality guidelines, pollution indices, macrobenthic community structure and the biotic index M-AMBI. Sediment samples for metal and macrobenthic analyses were collected quarterly at seven sites during 2016−2017 using a Van Veen sediment grab sampler. Sediment samples were acid digested using a microwave digester and analysed for metal concentrations using ICP-OES. Highest metal concentrations (Cd, Cr, Cu, Ni and Zn) were associated with areas most affected by industrial activities, while concentrations of most metals at the remaining sites were low. Pollution indices confirmed significant enrichment of Cd, Cr and Cu in bulk terminal sediment. Sediment quality guidelines revealed potential toxicity associated with Cu, Cr and Ni. The dominant taxa were Halmyrapseudes digitalis (two sites), Mediomastus capensis (three sites) and Sigambra parva (two sites). A significant inverse correlation existed between pollution indices and M-AMBI scores, confirming the adverse effect of metals on habitat quality. The need for a biomonitoring programme incorporating relevant biotic and abiotic indices is emphasised to assess the long-term effects of sediment contamination on aquatic communities in South African estuarine environments.