The Impact of Christchurch City (New Zealand) on Heavy Metals in Sediments of the Avon-Heathcote Estuary

Abstract

This paper reviews heavy metal (Cr, Cu, Fe, Mn, Ni, Pb, Zn) content in the clay fraction (<4 µm) of soils, suspended sediment, surface sediment, and core sediment associated with the Avon-Heathcote Estuary. Despite the estuary's low clay content (<10%), significant metal and organic matter trends are apparent in the clay fraction, which are less obvious in parallel studies of silt (4-63 µm), sand (>63 µm), and total sediment. Clay fraction depth profiles record periods of high heavy metal input in sediments deposited slowly but not in sediments deposited rapidly. Most metals, organic matter, mud, and Fe oxides accumulate in a broad anaerobic band across the western area of the estuary. Organic matter and metal concentrations are increasing towards the surface in depth profiles of this zone. This pattern combined with the increasingly eutrophic state of the estuary suggests more serious heavy metal contamination in the future.