Thesis (M.Sc.)--Memorial University of Newfoundland, 1997. / Bibliography: leaves 87-98.

Ihis work on the Sado outer estuary (western coast of Portugal) considers its bio-sedimentary characterization, and evaluates the prevailing hydrophysical and sedimentary environmental conditions. The quality status of the estuary is discussed. The thesis is based on the analysis of superficial sediments and benthic macrofauna collected from 133 sites, and on hydrodynamical data obtained from a mathematical model. The environmental variables considered were the superficial sediment temperature, granulometry and organic matter content, together with the water current velocities, flow and shear stress. The macrofaunal characterization and the analysis of the state of disturbance was based on a study of the composition, structure and spatial distribution of faunal assemblages and their relationship to the prevailing environmental conditions. The Sado was shown to be inhabited by an abundant and diversified fauna with high biomass. Two major faunal assemblages have been identified, a marine and an estuarine community, separated by a transition region. The estuarine community comprises the majority of the area and contains important subdivisions. The regions identified have been shown either to be controlled by anthropogenic inputs or to reflect mainly the effects of natural forces. The main structuring factors influencing the benthos are the hydrodynamic conditions, coupled with sediment type, and organic matter of natural and anthropogenic origin. Sedimentary organic enrichment effects have been noted in all the areas studied and in general the Sado outer estuary reveals signs of eutrophic conditions. In the more disturbed regions the macrofauna data also suggest chronic toxicity effects. Although disturbance effects due to anthropogenic inputs are suggested through the biosedimentary approach, the estuary as a whole can not be considered badly polluted. However, defaunated, impoverished and over-enriched areas, appear as a result of localised severe pollution indicating the need to improve effluent treatment systems. The methodological approach followed in this study has been shown to be effective in assessing the quality status of the Sado outer estuary. Multivariate and direct gradient analysis proved to be very useful methods and a detailed analysis of the macrofaunal species has been shown to be effective in the detection of organic enrichment effects in some of the areas. The extreme aspects of the gradients were identified by all the analytical techniques, but the univariate methods were shown to be poor at discriminating the more subtle effects.

A criação de camarões marinhos em cativeiro tem sido acusada de causar sérios impactos ambientais, sobretudo em função do lançamento de grandes quantidades de nutrientes e metais pesados nas águas estuarinas. Diversos estudos realizados nos principais estados produtores de camarão no Brasil, através do uso de fatores de emissão, estimaram as cargas destes poluentes para seus principais estuários. Neles ficou caracterizada a importância desta atividade como fonte de nutrientes, uma vez que a carcinicultura dominou as emissões de nitrogênio para os estuários dos rios Açu (RN) e Jaguaribe (CE). Ocorre que esses estudos consideraram a forma de cultivo de camarão, predominante há alguns anos, a qual estava baseada em uma produção intensiva. Desta forma, devem ser consideradas as alterações nos processos produtivos dessa atividade, e precisam ser determinados novos fatores de emissão. O estuário do rio Potengi (RN), objeto de estudo, apresenta características que o tornam bastante susceptível a elevadas depreciações da qualidade de suas águas, pelo fato de nessa bacia hidrográfica estar implantada a capital do estado, cidade com maiores contingente populacional e grau de urbanização do RN. O presente trabalho trata da determinação de novos fatores de emissão relativos a nutrientes e a metais pesados para a carcinicultura, com base na realidade atual desta atividade no estuário do rio Potengi e avalia, também a importância da carcinicultura como fonte de nutrientes e metais pesados para o referido estuário. Estes novos fatores de emissão foram determinados e serviram como base para estimativa da carga anual da carcinicultura; também foram determinadas as cargas de outras fontes naturais e antrópicas presentes no ecossistema de estudo o que permitiu verificar que a carcinicultura, apesar de não ser a atividade predominante, constitui fonte ) importante de nitrogênio (5,28%), cobre (10,54%) e zinco (14,04%). / The creation of marine shrimp in captivity has been blamed for causing serious environmental impacts, particularly through the release of large amounts of nutrients and heavy metals in estuarine waters. Several studies in the major shrimp-producing states in Brazil, through the use of emission factors, estimated the loads of these pollutants to their main estuaries. In them was a characteristic aspect of this activity as a source of nutrients, since the carciniculture dominated the emission of nitrogen to the estuaries of the Acu (RN) and Jaguaribe (CE). It turns out that these studies considered the form of shrimp farming, prevalent a few years ago, which was based on an intensive production. Thus, should be considered the changes in production processes of this activity, and need to be certain new emission factors. The estuary Potengi (RN), the object of study, has characteristics which make it very susceptible to high depreciation of the quality of the water, because this basin has been introduced to the state capital city with the highest overall population and degree of urbanization of the RN. This paper deals with the new emission factors for nutrients and heavy metals in the carciniculture, based on the current reality of this activity in the estuary Potengi and evaluates also the importance of carciniculture as a source of nutrients and heavy metals in that estuary. These new emission factors were determined and served as a basis to estimate the annual load of carciniculture, were also determined loads of other natural and anthropogenic sources in the ecosystem of the study that showed that the carciniculture, though not the predominant activity, constitutes an important source of nitrogen (5.28%), copper (10.54%) and zinc (14.04%).

The influence of sedimentary variables on the structure and function of infaunal estuarine and marine communities is well studied but less is known of the influence of biota on sediment properties. Feeding and burrowing activity, locomotion, the production of faecal pellets and biological secretions (bioturbation) have important implications for sediment structure, chemistry, transport characteristics and the flux of nutrients and contaminants. Although spatial and temporal patterns in bioturbation have been studied to some extent, little attention has been given to the effects of pollution. The present study examines the effects of an intertidal petrochemical discharge into the Humber estuary (UK), from BP chemicals (Saltend) Ltd on the structure and function of the communities. Field and laboratory techniques were used to determine the effects of community change on bioturbation potential. In addition, a laboratory flume was constructed to measure sediment erosion potential with field measurements being taken using a Cohesive Strength Meter (CSM). The physico-chemical properties of the sediment, changes to the infaunal community structure, bioturbation potential and the interaction of these variables were used to explain differences between the erosion potential of sediments subject to varying levels of contamination. The main study was carried out on the Saltend mudflats near Hull, with sites at various distances from the outfall being used. A further set of control sites on the adjacent, and largely unaffected, mudflat at Paull were also used. In terms of the sediment properties, sites closest to the outfall showed the greatest degree of anoxia and the highest chlorophyll-a and carbohydrate concentrations, with all three parameters being seasonally influenced. No consistent spatial or temporal patterns were found for any of the other parameters (water and organic content, particle size). Whilst the infaunal communities were characteristic of estuarine areas, macrobenthic community response followed the Pearson & Rosenberg (1978) model for organic discharges with high abundance and low species diversity being associated with the more polluted sediments. Close to the discharge, there was an impoverished community consisting predominantly of highly abundant oligochate worms. With increasing distance from the outfall, species diversity and biomass increased with Hediste diversicolor becoming increasingly dominant and the appearance of Corophium volutator, Streblospio shrubsolii and Macoma balthica. Bioturbation potential was significantly reduced (in terms of depth and burrow volume and density) by increasing effiuent concentrations and with proximity to the discharge. The diversity of both feeding and sediment modification guilds was also reduced as a result of the discharge. Both field and laboratory studies indicated a stabilising effect of this type of pollution. Using the CSM, critical shear stress values were found to be significantly lower from unpolluted sites, indicating higher erosion potential, than those from sites close to the discharge. As a result of this, the total mass of sediment eroded from unpolluted sites was significantly higher than that from polluted areas. A similar trend was observed in the laboratory with sediments treated with an effluent concentration of 32% being considerably more stable than untreated sediments. Flume studies also indicated the stabilising effect of pollution with suspended particulate matter (SPM) concentrations and mass of sediment being transported as bedload being significantly higher for unpolluted sediments. These differences in erosion potential were attributed to the direct effects of the effiuent on the physico-chemical properties of the sediment, the effects of the effiuent and sediment type on macrofaunal community structure and function and the differences in bioturbation potential between sites. The implications of these findings in the wider context of coastal management are discussed.

A criação de camarões marinhos em cativeiro tem sido acusada de causar sérios impactos ambientais, sobretudo em função do lançamento de grandes quantidades de nutrientes e metais pesados nas águas estuarinas. Diversos estudos realizados nos principais estados produtores de camarão no Brasil, através do uso de fatores de emissão, estimaram as cargas destes poluentes para seus principais estuários. Neles ficou caracterizada a importância desta atividade como fonte de nutrientes, uma vez que a carcinicultura dominou as emissões de nitrogênio para os estuários dos rios Açu (RN) e Jaguaribe (CE). Ocorre que esses estudos consideraram a forma de cultivo de camarão, predominante há alguns anos, a qual estava baseada em uma produção intensiva. Desta forma, devem ser consideradas as alterações nos processos produtivos dessa atividade, e precisam ser determinados novos fatores de emissão. O estuário do rio Potengi (RN), objeto de estudo, apresenta características que o tornam bastante susceptível a elevadas depreciações da qualidade de suas águas, pelo fato de nessa bacia hidrográfica estar implantada a capital do estado, cidade com maiores contingente populacional e grau de urbanização do RN. O presente trabalho trata da determinação de novos fatores de emissão relativos a nutrientes e a metais pesados para a carcinicultura, com base na realidade atual desta atividade no estuário do rio Potengi e avalia, também a importância da carcinicultura como fonte de nutrientes e metais pesados para o referido estuário. Estes novos fatores de emissão foram determinados e serviram como base para estimativa da carga anual da carcinicultura; também foram determinadas as cargas de outras fontes naturais e antrópicas presentes no ecossistema de estudo o que permitiu verificar que a carcinicultura, apesar de não ser a atividade predominante, constitui fonte ) importante de nitrogênio (5,28%), cobre (10,54%) e zinco (14,04%). / The creation of marine shrimp in captivity has been blamed for causing serious environmental impacts, particularly through the release of large amounts of nutrients and heavy metals in estuarine waters. Several studies in the major shrimp-producing states in Brazil, through the use of emission factors, estimated the loads of these pollutants to their main estuaries. In them was a characteristic aspect of this activity as a source of nutrients, since the carciniculture dominated the emission of nitrogen to the estuaries of the Acu (RN) and Jaguaribe (CE). It turns out that these studies considered the form of shrimp farming, prevalent a few years ago, which was based on an intensive production. Thus, should be considered the changes in production processes of this activity, and need to be certain new emission factors. The estuary Potengi (RN), the object of study, has characteristics which make it very susceptible to high depreciation of the quality of the water, because this basin has been introduced to the state capital city with the highest overall population and degree of urbanization of the RN. This paper deals with the new emission factors for nutrients and heavy metals in the carciniculture, based on the current reality of this activity in the estuary Potengi and evaluates also the importance of carciniculture as a source of nutrients and heavy metals in that estuary. These new emission factors were determined and served as a basis to estimate the annual load of carciniculture, were also determined loads of other natural and anthropogenic sources in the ecosystem of the study that showed that the carciniculture, though not the predominant activity, constitutes an important source of nitrogen (5.28%), copper (10.54%) and zinc (14.04%).

Persistent organic pollutants (POPs), including polychlorinated biphenyls (PCBs) are widespread in aquatic systems, they can bioaccumulate in the tissues of aquatic organisms, especially fish as they occupy a position near the top of the aquatic food web. PCBs are among the most toxic substances and have been shown to cause many adverse effects to humans and wildlife. High health risks are associated with populations that follow a diet high in fat content such as fish and shellfish in which PCBs bioaccumulate. Given the importance of industries and the potential health concerns of exposure to PCBs, the lack of information on environmental levels of PCBs in South Africa (SA) is significant and concerning. Less attention has been directed to analysis of PCBs in the South African environments due to high cost and lack of appropriate equipment. This study was the first conducted in order to assess the levels of PCBs in the environment of Nelson Mandela Bay Municipality (Port Elizabeth). The research was directed at determining the PCB levels in water, sediments, fish and mussels collected in the Nelson Mandela Bay Municipality. The sampling sites, North End Lake (NEL) and Port Elizabeth Harbour (PEH) were selected based on their location and the importance of activities taking place in these areas. In total 456 samples of water (dissolved and particulate phases), sediments, mussels and tissues of fish were analysed. Suitable analytical methods were based on the equipment and materials available at the Nelson Mandela Metropolitan University. Gas chromatography-mass spectrometry (GC/MS) was used to quantify PCBs in the samples using the internal standard method. Six indicator congeners (PCB nos. 28, 52, 101, 138, 153, 180) were chosen because they are mainly present in most PCB mixtures in environmental samples and they are recommended for regular monitoring. These congeners represent about 50% of the total non-dioxin like (NDL) PCBs in food. All these congeners were detected in the samples analysed. The total PCB concentrations in the sediments from the NEL and PEH ranged from 1.60 to 3.06 and from 0.56 to 2.35 ng g-1 dry weight, respectively. The concentrations of total PCBs in Mytilus galloprovincialis ranged from 14.48 to 21.37 ng g-1 wet weight and from 20.84 to 31.34 ng g-1 wet weight in Perna perna. Total PCBs in water ranged from 0.18 to 0.355 ng L-1. The concentrations of total PCBs in the liver, gonads, gills and muscle were 95.69, 57.49, 44.63, 34.14 ng g-1 lipid weight in Cyprinus carpio and 119.73, 59.21, 49.78, 34.63 ng g-1 in Oreochromis mossambicus, respectively. Fish liver was the most contaminated organ due to its high lipid content compared to other parts of fish analysed. The NEL was found to be more contaminated than the PEH. The main potential sources of PCB pollutants in both areas of this study are industrial and municipal discharges. The NEL is surrounded by many industries and serves as a potential pollutant sink due to wastewater and inflow entering into this lake. Four 0.227 kg meals of the edible part of fish (muscle) per month were recommended based on the non-cancer health endpoint and one 0.227 kg meal per month was recommended based on the cancer health endpoint. This research contributed to notify the public and relevant governmental departments on the PCB pollution status of sediments, water and aquatic life in the PEH and NEL.

Contamination of recreational waters with fecal waste, indicated by the presence of enterococci, can have consequences for human and ecosystem health. The difficulty in determining the extent and origin of fecal pollution in dynamic estuarine systems is compounded by contributions from sources including septic tanks and agricultural runoff. This study investigated fecal pollution at five sites with variable hydrological conditions in the St. Lucie Estuary and Indian River Lagoon. The distribution and occurrence of enterococci was assessed using traditional cultivation. A human-associated microbial source tracking assay was validated and applied in these estuaries using qPCR. Results demonstrated a correlation between enterococci concentrations, rainfall, and salinity. The human-associated assay was sensitive and specific in the lab; however, human fecal pollution was not detected in the field even though samples contained high levels of enterococci. This study highlights the importance of expanding the range of water quality assessment. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection

The Port of Durban is a resource utilised by a wide range of stakeholders. The water quality of this resource is a prerequisite for sustaining the preferred uses of the bay for future generations. Given the extent of development in the port the abundance of fauna and flora is remarkable. Based on the current literature available the management of the port uses a combination of international and local standards to manage the water resource. An associated problem however is that the local legislation does not address the heart of the pollution problem - the polluter. This is highlighted in all chapters of this thesis, as the South African water quality guidelines are not legally enforceable, and do not take into account the combined use of resources. The uncontrolled nutrient loads and pollution present in the port system could ultimately affect the ecosystem health. This is amplified by apparent inability of officials to protect the receiving environment of the Port of Durban. The subsequent condition of water quality in the port compared with the Department of Water Affairs guidelines indicates that there is less than 5% compliance with the target water quality variables. in comparing the same water quality to international water quality Legislation the compliance percentage increased marginally, however the bacterial contamination and nutrient contamination of the resource is apparent even with more relaxed international comparisons. The noticeable cause was clearly evident when comparing results, indicating extensive unacceptable bacterial and nutrient contamination emanating from stormwater systems from the city of Durban, and highly urbanised river catchments. Based on the water quality results it is highly recommended that sustainable environmental management practices be implemented to protect and address the water resource. The metropolitan authorities need to investigate the origins of the stormwater pollution and dialogue must ensue between Portnet and the City to reach consensus on receiving water quality objectives with the aim of compiling a water management policy. / Thesis (M.A.)-University of Natal, Durban, 2001.

The South Slough Estuary is located off Coos Bay along the southern coast of Oregon. It is divided into two channels that meet and continue to Coos Bay at the Charleston Harbor. There are six major contributing streams to South Slough. After rainfall events, the level of coliform bacteria in the slough increases because of stream bacteria loading. This is due to cattle grazing in the drainage areas, failed septic systems from private homes, and sewage sludge applied to the County landfill, which drains into the slough. The Oregon Health Division has enforced a Sanitation Management Plan for Commercial Shellfish Harvesting in South Slough that specifies closure of commercial shellfish harvesting for certain rainfall and flood events. The purpose of this study is to analyze and improve the current understanding of the hydraulics and water quality of the South Slough Estuary. This was achieved by calibrating the South Slough using the water quality model CEQUAL- W2. It was calibrated for the following parameters water surface elevations, velocity, temperature and total dissolved solids. A management analysis was also done analyzing the transport of bacteria and a conservative tracer. Model predictions for water surface elevations at one of the monitoring sites, Hinch Road Bridge, was significantly lower than measured elevations. There was an excellent correlation of velocity, and reasonable timing of peaks due to tidal effects. Model predictions for temperature and total dissolved solids match measured values well. To improve the accuracy of the model the following was recommended; install a raingage in the South Slough, measure temperature and constituent concentrations at inflow locations, survey the S4 current meter, new soundings performed of the Winchester Creek arm and at the Hinch Road Bridge gaging station, and investigate the possibility of an obstruction near the Hinch Road Bridge gaging station.

Three approaches were employed to examine the effects of elevated sediment trace metal concentrations on estuarine/marine macrobenthic invertebrate assemblages. The initial study examined macroinvertebrate communities along a known polymetallic gradient, Lake Macquarie, NSW (gradient study). The second study experimentally tested if sediments sourced from different locations within Lake Macquarie differentially influenced the recolonisation of benthic invertebrates. The third study investigated the different recolonisation patterns of benthic invertebrates into sediments spiked with increasing concentrations of sediment-bound cadmium. In the Lake Macquarie gradient study, four locations (Cockle Bay, Warner's Bay, Kooroora Bay and Nord's Wharf) were sampled in winter 2000 and summer 2003 using a hierarchical design (location > site > plot). On both sampling occasions, the sediments showed strong gradients in lead, cadmium and zinc concentrations emanating from the Cockle Bay industrialised region in the lake's north, with concentrations being significantly lower in the most southern and less urbanised location (Nord's Wharf). In general, concentrations of lead, cadmium and zinc in the sediments increased among locations in the following order: Nord's Wharf > Kooroora Bay > Warner's Bay > Cockle Bay. AVSJSEM analyses indicated that in some sites in Cockle Bay, and to a lesser extent Warner's Bay, SEM concentrations exceeded their molar equivalence of AVS, indicating the potential for trace metals to be labile within the porewaters. Granulometry also changed along the gradient, with a higher proportion of silt/clay occurring in the locations with high metal concentrations. Conversely, the percentage of total organic carbon was higher in the less contaminated locations. In winter 2000, changes in benthic communities along the gradient supported the a priori hypotheses, with diversity and richness being greater in locations with lower concentrations of metals. Polychaetes were most numerous in Cockle Bay and Warner's Bay, whilst bivalves and gastropods were more abundant in Nord's Wharf and Kooroora Bay. Crustaceans were more numerous in Nord's Wharf; with all other locations having similar, lower, abundances. Ordination maps of the assemblages provided relatively clear separation of the assemblages among locations, with nonparametric multivariate analysis of variance (NPMANOVA) and subsequent pair-wise comparisons finding significant differences among the assemblages from all locations. SIMPER analyses found the highest level of dissimilarity was between the Nord's Wharf and Cockle Bay assemblages - primarily attributable to differences in the relative contributions of isopods; tellenid bivalves; and the polychaete families Spionidae, Opheliidae and Nephytidae. Weighted Spearman rank correlations (BIOENV) identified cadmium (Pw =0.74) as the strongest environmental (single or combination) variable to correlate with biotic assemblages. Benthic patterns along the gradient were less defined in summer 2003 due to a dramatic reduction in the abundance and diversity of fauna in Nord's Wharf. This decline was possibly attributable to a sustained reduction in salinity caused by a prolonged rainfall event. With the exception of Nord's Wharf, trends in the community indices and abundances of key taxa among the other locations were similar to those reported in winter 2000. Multivariate analyses discriminated the benthic assemblages from the four locations, with the findings from the NPMANOVA pair-wise comparisons indicating that the assemblages from all four locations were significantly different. SIMPER analyses showed the highest level of dissimilarity was between Nord's Wharf and Warner's Bay, with these differences being primarily attributable to their relative abundances of amphipods and polychaetes from the families Spionidae, Cirratulidae, Opheliidae and Capitellidae. BIOENV found that the combination of the sedimentary concentrations of cadmium and iron provided the best correlation (Pw =0.73) with biotic patterns, with similar correlations occumng with the addition of lead and its covariate, zinc (Pw =0.72). The combined findings from the gradient study established a strong correlation between trace metal concentrations within the sediments and suite of univariate and multivariate measurements. The low abundance and diversity of fauna in Nord's Wharf in the summer of 2003 highlighted the dynamic changes which can occur in the distributions of macrobenthic invertebrates. Although the study indicated that there was a strong relationship between trace metal concentrations and benthic community structure, the study was correlative, and requires subsequent experimental testing to confirm the causality of the observed relationships. The second component of the research was a translocation experiment using benthic recolonisation as an end-point. The experiment was performed to identify if the sediments, and not location, were influencing the composition of benthic assemblages in Lake Macquarie. Sediments were collected from three locations (Cockle Bay, Warner's Bay and Nord's Wharf), defaunated, and transplanted in three new locations along the south-east edge of the lake. At each location, 10 containers of each treatment were randomly placed in the sediment and allowed to recolonise for 22 weeks. Upon retrieval, the benthic communities were sampled and enumerated in conjunction with a variety of chemical and sedimentary measurements. Ten replicate invertebrate samples were also collected in the sediments adjacent to the experiment (ambient samples) at the completion of the experiment. Due to human interference, the containers from only two locations were analysed. Upon retrieval, pH and redox profiles of the sediments were similar to those expected in natural sediments. In general, concentrations of metals were low in the porewaters; however, iron precipitation on the porewater collection devices may have artificially increased the diffusion of metals, increasing concentrations near the sediment-water interface. Concentrations of SEM exceeded their AVS equivalence in some samples taken from the Cockle Bay and Warner's Bay treatments. Two-way ANOVAs found significant interactions between location and sediment treatments in diversity, evenness and the number of polychaetes, as well as significant differences in the number of capitellids and crustaceans among locations. Post-hoc comparisons of means found the Nord's Wharf sediment contained a higher mean number of individuals than the other treatments, including the ambient samples. nMDS ordination plots for both locations provided poor graphical discrimination of the assemblages among treatments; however, NPMANOVA detected significant location and treatment interactions. In both locations, pair-wise comparisons indicated that the assemblages within the Nord's Wharf treatments were significantly different to the Cockle Bay, Warner's Bay and ambient assemblages. No significant differences were detected between the Cockle Bay and Warner's Bay assemblages at either location. SIMPER analyses found the highest level of dissimilarity occurred between the ambient assemblages in Location 2 and the Nord's Wharf treatment, primarily due to the relative difference in the abundances of Capitellidae, Spionidae, Oweniidae, Nereididae and isopods among the assemblages. The findings from the translocation experiment suggest that the sediments are influencing the recolonisation of benthos. However, because differences were not detected between the Cockle Bay and Warner's Bay treatments, the approach used in the study shows potential as an in situ technique which could be used to assess the potential ecological risks of sediments fiom specific locations. Excluding cost and time considerations, the technique's primary disadvantage is the lack of a true control. As a result, the technique can only identify if the sediments are modifying benthic recolonisation, and not causality. The final component of the research experimentally tested if elevated concentrations of sediment-bound cadmium affected benthic invertebrate recolonisation. Sediments from the south coast of New South Wales (Durras Lake) were defaunated, and spiked with cadmium under anaerobic conditions to obtain three targeted cadmium concentrations: control (<O.1 ug/g), Low-Cd (15 Cd ug/g) and High-Cd (150 Cd ug/g). The physio-chemical properties of the waters and porewater concentrations of cadmium were monitored over a 28-day equilibration period, with declines in pH mediated with the addition of NaOH(aq). At the end of the equilibration period, porewater concentrations of cadmium were low in the Low-Cd and High-Cd treatments (maximum <l.5 ug/L in High-Cd), and below the detection limit in the control. Cadmium was not detected in the control sediments, with concentrations in the Cd-Low and Cd-High sediments exceeding their targeted concentrations, with final mean concentrations of 17 ug/g and 183 ug/g, respectively. The experimental design was similar to that employed in the translocation experiment, with 10 containers from each treatment transplanted into the sediments at three locations within Lake Macquarie. After 20 weeks, the containers were collected, along with benthic invertebrate samples from the ambient sediments. Data was not used from Location C due to extensive sediment deposition on the transplanted treatments. Significant declines occurred in the concentrations of cadmium in both the Low-Cd and High-Cd sediments, with the greatest loss occumng in the surficial sediments. The loss of cadmium was probably due to the differential loss of the fine fraction through physical means (hydrodynamic) rather than fluxing, as it assumed that the cadmium was primarily sediment-bound and relatively insoluble under anoxic conditions. Mean porewater concentrations of cadmium were below the detection limit in the control treatments; < 1 ug/L in the Low-Cd treatment, and generally < 2ug/L in the High-Cd, with the exception of some samples in Location B (maximum 5.6 ug/L) Concentrations of ammonia were low in the porewaters from the surficial sediments, with concentrations being significantly higher, and potentially toxic, in the anoxic porewaters (7 cm depth). In comparison to the previous recolonisation experiment, the number of individuals which recolonised the cadmium-spiked treatments was low, and significantly lower than the mean number of individuals sampled in the ambient sediments. No significant differences were detected among the treatments or locations (and their interactions) in diversity (H'), richness (d) or evenness (J). The number of polychaetes and molluscs significantly differed among the treatments, with post-hoc analyses indicating these differences were not among the cadmium-spike treatments, but were due to a greater mean abundance of these taxa in the ambient sediments. A significant interaction between treatment and location was detected in the mean abundance of crustaceans, with the ambient sediments having significantly lower mean abundances in both Location A and B. Ordination plots of the experiments in Location A and B provided poor graphical discrimination among the spiked treatments, although the ambient assemblages appear to be separated from the cadmium-spiked assemblages. NPMANOVA detected a significant interaction between treatments and locations, as well as among treatments. In both Location A and B, pair-wise analyses found the assemblages in the ambient sediments to be significantly different to the assemblages in all three cadmium treatments, with no differences being detected among the latter. SIMPER analyses found the highest levels of dissimilarity occurred between the spike-treatments and the ambient sediments, with these differences being primarily due to the relatively higher abundance of decapods in the spiked treatments, and capitellids in the ambient sediments. The cadmium-spiking component of the experiment clearly illustrated that artificially increasing the trace metal concentrations of metals in estuarine sediments is a complex process which needs to be performed in a methodological manner in order to obtain homogenous treatments with low porewater concentrations, and minimal artefacts. Furthermore, the results confirmed that the equilibration time for sediments can be extensive (several weeks), even in the case of organically rich sediments. The timing of the experiment (commenced late summer, February, 2003) appears to the major factor for the relatively low recolonisation rates, with the experiment missing the main larval recolonisation period between spring and early summer. Even in the highest treatment, elevated concentrations of cadmium did not appear to affect benthic recolonisation. This finding is supported by other experimental studies which suggest that concentrations of a single isolated metal must considerably exceed current guideline values (or contain high porewater concentrations) in order to elicit a biological effect. Nevertheless, as trace metals generally co-occur with other contaminants - with the response of multiple contaminants being possibly additive or synergistic - a conservative guideline value may be suitable in the interim as a precautionary measure. The findings of this thesis suggest that elevated concentrations of trace metal mixtures in estuarine sediments can affect the structure and composition of benthic communities; however, identifying causality is difficult. Although there has been an increase in the use of manipulative field experiments as a means of reducing the confounding influence of covariables found in field studies, this approach also has limitations, e.g. spatial and temporal scale issues, container effects, cost and biogeochemical changes to the sediments. Measuring stress at a community level is a fundamental component of estuarine risk assessment programs; and in isolation this approach can produce subjective and confounded findings. In order to accurately assess the risks associated with trace metal contaminated sediments, an integrated approach (e.g. weight of evidence) is required, one which uses multiple lines of evidence sourced from various chemical, environmental biological measurements.