Spatial and temporal variations in selected heavy metals in water and sediment from the Mhlathuze Estuary, Richards Bay

Abstract

Spatial and temporal variations in water (total, dissolved and particulate), and sediment concentrations of seven heavy metals, Al, Cr, Cu, Mn, Pb and Zn from the Mhlathuze Estuary were analyzed. Effects of environmental factors on the metals in the estuary were also investigated. In water, metals concentrations varied spatially as well as seasonally with highest concentrations of Al Cr, Fe, Mn and Zn recorded in summer. Partitioning of metals was influenced by environmental factors including dissolved oxygen, turbidity and pH with two groups being identified, that is, metals that increased with increasing salinity and metals that increased with increasing turbidity. In sediment, metal concentrations showed little seasonal variation. There were, however, significant spatial differences in metal concentrations, with muddy, high organic areas of the estuary consistently having highest concentrations of metals as compared to other sites. These results suggest a high degree of heavy metal contamination in the Mhlathuze Estuary and also stress the importance of incorporating sediment metal analysis in any assessment of metal pollution in estuarine environments. Key words: Estuaries, heavy metals, pollution.