Surficial sediment-heavy metal associations in the avon-heathcote estuary, new zealand

Abstract

Adsorbed Zn, Cu, Pb, Cr, and Ni were extracted from surficial sediment samples of 330 sites in the Avon-Hcathcotc Estuary. Total adsorbed heavy-metal concentration (TAHM) in each site was shown to be highly correlated with mean sediment surface area. However, the relative contributions of sediment fractions to TAHM varied bimodally with decreasing particle size. In particular, the very fine silt and clay fractions showed less contribution to TAHM than coarser sediment grades including fine sand. This is because fine sediment particles tend to flocculate in saline conditions, thereby decreasing the effective adsorptive surface area of the sediments. This result implies that, paradoxically, cstuarinc sediments which consist predominantly of fine silts and clays may have fewer hcavymetal ions to contribute to the chemical environment of the estuary than coarser sediments. Show more