<P> Natural organic matter (NOM) on the surface of resuspended particles influences the partition of metal ions between free dissolved organic matter (DOM), and the particulate species. It also affects the size distribution of floes under agitation. Equilibrium between dissolved organic and particulate organic matter should, therefore, be an important indicator for predicting metal ion exchange. </p> <p> We examined the exchange of cadmium along a pH edge and compared aqueous, organic, and particulate forms of the metal ion in reactors containing either settled or resuspended sediments. A pH edge profile between 3 and 8 shows two regions of speciation: above and below pH 6.2, which corresponds to a 1 : 1, H : Cd exchange. At low pH, cadmium remains in the free form when sediments are settled, but, upon resuspension, about half of it transfers to the dissolved organic and particulate forms. On the other hand, at high pH, all cadmium is particulate in both cases. In both cases there is also a release of DOM centred at pH 6.2, followed by readsorption at higher pH values. </p> <p> The interesting finding is that cadmium binding on particles appears independent of the surge in DOM, as though cadmium is weakly bound to DOM and strongly bound to particles. We can assume that two types of organic matter exist, one dissolved, one particulate. </p> <p> To fix size distribution, the sediment/metal ion mixture was put in a Couette flocculator and subjected to a uniform shear stress. Then, the partitioning of the metal ions between the solution and sediment phases was determined. A distribution coefficient, KD was calculated for each metal ion. A correlation between log KD and log K (hydrolysis constant) was apparent, and our data was consistent with the reported metal ion binding to both sediments and artificial surfaces. We envision that organic matter accumulating on the particle creates a polyelectrolyte domain responsible for greater binding capacity. We propose that an increase in metal ion binding with increasing particle size is due to this polyelectrolyte effect, where binding is governed by particle volume, and not surface area. </p> / Thesis / Master of Science (MSc)

Contaminated sediments pose a direct risk to sediment fauna and have the potential to affect other benthic assemblages. Disturbances that resuspend and remobilise contaminants may impact on filter-feeding, hard-substrate organisms that live immediately above sediments. This thesis uses laboratory and field manipulations to examine the impact of metal-contaminated sediments on sediment fauna and hard-substrate fauna simultaneously. It also compares the response of assemblages to metal contamination in a temperate and polar ecosystem. Simulated resuspension exposures in the laboratory indicated that contaminated sediments have the potential to affect hard-substrate organisms. Spirorbid polychaetes responded to both aqueous metals and to resuspended, particulate-bound metals. Impacts on hard-substrate fauna were however, not observed in manipulative field experiments using metal-spiked sediments. The recruitment and cover of hard-substrate organisms were either not affected or enhanced above contaminated sediments. In contrast, metal contamination had direct negative effects on sediment fauna, with a reduction in the abundance of most taxa. Results suggest that sediment fauna may interact with hard-substrate fauna through physical and/or biological mechanisms. In a reciprocal transplant experiment, established Antarctic hard-substrate assemblages were also unaffected by contaminant concentrations at an impacted site. Overall, metal-contaminated sediments are unlikely to pose as serious a threat to hard-substrate fauna as they do to sediment fauna. Contaminated sediments are not restricted to industrialised regions, and human activities in Antarctica have resulted in localised contamination near research stations. Although Antarctic assemblages are thought to be more sensitive than temperate assemblages to contaminants, few studies have explicitly examined this. Little evidence was found to support the theory that Antarctic assemblages are more susceptible to contaminated sediments. The response of Antarctic and temperate assemblages in the field to metal-contaminated sediments over a 10-11 month period was comparable. Responses were of a similar magnitude, despite differences in the composition of assemblages. In 10-d toxicity tests, the mortality of a common Antarctic hard-substrate organism was relatively insensitive to aqueous Cu, Zn and Pb. These results suggest that using current sediment quality guidelines from Australia may be a useful screening tool to assess the risk associated with contaminated sediments in Antarctica.