Heavy-metal contaminants in Tamaki Estuary: impact of city development and growth, Auckland, New Zealand

Tamaki Estuary is a large, semi-enclosed water body on the eastern side of the Auckland metropolitan area. The long and relatively narrow channel of the estuary (ca. 17 km in length) is surrounded by an urbanised and industrialised catchment. The catchment is noted for more than 600 industrial premises in addition to a range of other human activities associated with pastoral and urban land-use changes during the last 150 years. The study of seven estuary cores shows that sedimentation rates as well as the sediment coarse fraction have increased with the development of the catchment. Significant enrichments were also found for Cd, Cu, Pb, and Zn in the upper part of the cores, compared to the much lower concentrations found below 40-50 cm (considered to represent pristine background levels). Spatial association of contaminants with industrial areas and yacht anchorages, and temporal enrichments associated with the intensive urbanisation and development of the catchment since 1945 indicate that these pollutants are related to anthropogenic activities.