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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Destruction of polycyclic aromatic hydrocarbons (PAH's) and aliphatic hydrocarbons in soil using ball milling

Magoha, Happy Steven Unknown Date (has links)
This study involves the use of ball mill as a mechanochemical reactor in the destruction of environmental contaminants. Although the technology has the potential to be used for a wide range of organic contaminants, this study focused on polycyclic aromatic hydrocarbons (PAH's) and aliphatic hydrocarbons. There are different methods for the remediation of the environmental contaminants such as biological, chemical and thermal techniques, most of which are costly. The ball mill is less costly as it involves low technology and little or no other chemicals seem to be needed to give complete destruction of the substances investigated. The mill is relatively easy to construct and can be made in different designs and dimensions to fit its intended purpose i.e. they can range from a laboratory scale to a very large industrial mill for the continuous processing of tonnes of material at a time. The process can be sealed so pollution from the mill is easy to control. In this study two classes of environmental contaminants were investigated. PAH's are common by-products of combustion and are found as contaminants in many soils. The other compounds investigated were the larger aliphatic hydrocarbons. These were chosen as being representative of the evaporated residues from fuel spills or leaks. A laboratory scale centrifugal ball mill with capacity of approximately 200 g was used for the study. The PAH's investigated were naphthalene, anthracene and phenanthrene. The aliphatic hydrocarbons n-eicosane and n-octacosane were used as the model compounds for hydrocarbon residues. Different soil types (scoria, clay soil, silica sand and slag) were spiked with a known amount of these contaminants. The ball milling was done under different milling conditions i.e. with different ball ratio and with different milling duration. In some experiments there was an addition of materials such as a potential free radical trap or metals to investigate the effect on the mechanochemical reaction. The samples were analysed using an ultrasonic extraction method (EPA METHOD 3550C) with GC and GC-MS analysis of the extract for the quantification of the residual contaminant in the soil and identification of possible secondary products and reaction intermediates. It was found that high destruction efficiency was achieved using milling times of between 120 and 150 minutes and high ball to soil ratios for example 7:1 ball mass to soil mass ratio. Also it was found that different type of soil had an influence on the mechanochemical reaction. A silica matrix was found to have a better destruction rate compared to scoria and clay soil. It was also found that the PAH compounds were more rapidly destroyed by ball milling than were aliphatic hydrocarbons. The addition of BHT was found to reduce destruction rate of both PAH's and aliphatic hydrocarbons. This suggests the mechanism of destruction may involve a free radical mechanism. Aluminium metal was observed to have no significant effect in the destruction. The presence of lubricants such as waxes in the contaminated soil appeared to inhibit the mechanochemical reaction although the mechanism is still uncertain. From this study it was concluded that, the ball mill has considerable potential as an effective, low cost method for the destruction of certain environmental contaminants.
2

Destruction of polycyclic aromatic hydrocarbons (PAH's) and aliphatic hydrocarbons in soil using ball milling

Magoha, Happy Steven Unknown Date (has links)
This study involves the use of ball mill as a mechanochemical reactor in the destruction of environmental contaminants. Although the technology has the potential to be used for a wide range of organic contaminants, this study focused on polycyclic aromatic hydrocarbons (PAH's) and aliphatic hydrocarbons. There are different methods for the remediation of the environmental contaminants such as biological, chemical and thermal techniques, most of which are costly. The ball mill is less costly as it involves low technology and little or no other chemicals seem to be needed to give complete destruction of the substances investigated. The mill is relatively easy to construct and can be made in different designs and dimensions to fit its intended purpose i.e. they can range from a laboratory scale to a very large industrial mill for the continuous processing of tonnes of material at a time. The process can be sealed so pollution from the mill is easy to control. In this study two classes of environmental contaminants were investigated. PAH's are common by-products of combustion and are found as contaminants in many soils. The other compounds investigated were the larger aliphatic hydrocarbons. These were chosen as being representative of the evaporated residues from fuel spills or leaks. A laboratory scale centrifugal ball mill with capacity of approximately 200 g was used for the study. The PAH's investigated were naphthalene, anthracene and phenanthrene. The aliphatic hydrocarbons n-eicosane and n-octacosane were used as the model compounds for hydrocarbon residues. Different soil types (scoria, clay soil, silica sand and slag) were spiked with a known amount of these contaminants. The ball milling was done under different milling conditions i.e. with different ball ratio and with different milling duration. In some experiments there was an addition of materials such as a potential free radical trap or metals to investigate the effect on the mechanochemical reaction. The samples were analysed using an ultrasonic extraction method (EPA METHOD 3550C) with GC and GC-MS analysis of the extract for the quantification of the residual contaminant in the soil and identification of possible secondary products and reaction intermediates. It was found that high destruction efficiency was achieved using milling times of between 120 and 150 minutes and high ball to soil ratios for example 7:1 ball mass to soil mass ratio. Also it was found that different type of soil had an influence on the mechanochemical reaction. A silica matrix was found to have a better destruction rate compared to scoria and clay soil. It was also found that the PAH compounds were more rapidly destroyed by ball milling than were aliphatic hydrocarbons. The addition of BHT was found to reduce destruction rate of both PAH's and aliphatic hydrocarbons. This suggests the mechanism of destruction may involve a free radical mechanism. Aluminium metal was observed to have no significant effect in the destruction. The presence of lubricants such as waxes in the contaminated soil appeared to inhibit the mechanochemical reaction although the mechanism is still uncertain. From this study it was concluded that, the ball mill has considerable potential as an effective, low cost method for the destruction of certain environmental contaminants.
3

The effects of human activities on stream water quality: case studies in New Zealand and Germany

Doyle, Paul Norman Unknown Date (has links)
Three case studies explore the effects of human activities on coastal streams and review measures to control the negative consequences of human activities. The first case study, an urban and a rural/forested stream in New Zealand, measured descriptors of water quality, including nutrients, dissolved oxygen and bacterial indicators of faecal contamination. The urban and rural catchments have stream-water qualities that fail to meet standards for fish life or bathing. Of the five sites studied, only one catchment, which had a substantial forest component (50%), had bacterial counts which meet the Australian Recreational Water-quality Guidelines for Secondary Contact (Faecal coliforms and enterococci, ANZECC, 2000) and the New Zealand Interim Guidelines for Freshwater Bathing (Escherichia coli, MofE, 2000). Only one site (which was downstream of a sediment-detention dam) had water clarity which met the Ministry of the Environment's (MofE, 1994) guideline for contact recreation.The results from this New Zealand case study indicate that the absence of riparian vegetation altered the temperature, pH and dissolved oxygen regime, that livestock increased levels of nitrate, turbidity and bacteria indicators of faecal contamination and that urban land use increased peak flows, peak-flow turbidity and bacterial indicators of faecal contamination and decreased base flows.The second case study, of a stream in the former Deutsche Demokratische Republik (East Germany), measured a similar suite of parameters and compared the German stream's 2001 water quality with records from 1991 (directly after the reunification of Germany). Measured levels of total nitrogen, nitrate, ammonium, phosphate and dissolved oxygen all showed significant improvements between 1991 and 2001. Stricter controls and regulations are thought to be the cause.The final case study reviews plans for an urban residential development in the catchment of the New Zealand rural/forested stream. Degraded sections of the stream could actually be improved if the development is sensibly managed. However, the sensitive nature of the receiving environment (a marine reserve) requires that measures be taken to avoid or mitigate any deleterious effects. Plans by the relevant authority, the North Shore City Council, are a major step forward from the unsustainable development of the neighbouring catchment. Still, more needs to be done. Ten recommendations have been made to ameliorate the potential negative impacts of the development.
4

The effects of human activities on stream water quality: case studies in New Zealand and Germany

Doyle, Paul Norman Unknown Date (has links)
Three case studies explore the effects of human activities on coastal streams and review measures to control the negative consequences of human activities. The first case study, an urban and a rural/forested stream in New Zealand, measured descriptors of water quality, including nutrients, dissolved oxygen and bacterial indicators of faecal contamination. The urban and rural catchments have stream-water qualities that fail to meet standards for fish life or bathing. Of the five sites studied, only one catchment, which had a substantial forest component (50%), had bacterial counts which meet the Australian Recreational Water-quality Guidelines for Secondary Contact (Faecal coliforms and enterococci, ANZECC, 2000) and the New Zealand Interim Guidelines for Freshwater Bathing (Escherichia coli, MofE, 2000). Only one site (which was downstream of a sediment-detention dam) had water clarity which met the Ministry of the Environment's (MofE, 1994) guideline for contact recreation.The results from this New Zealand case study indicate that the absence of riparian vegetation altered the temperature, pH and dissolved oxygen regime, that livestock increased levels of nitrate, turbidity and bacteria indicators of faecal contamination and that urban land use increased peak flows, peak-flow turbidity and bacterial indicators of faecal contamination and decreased base flows.The second case study, of a stream in the former Deutsche Demokratische Republik (East Germany), measured a similar suite of parameters and compared the German stream's 2001 water quality with records from 1991 (directly after the reunification of Germany). Measured levels of total nitrogen, nitrate, ammonium, phosphate and dissolved oxygen all showed significant improvements between 1991 and 2001. Stricter controls and regulations are thought to be the cause.The final case study reviews plans for an urban residential development in the catchment of the New Zealand rural/forested stream. Degraded sections of the stream could actually be improved if the development is sensibly managed. However, the sensitive nature of the receiving environment (a marine reserve) requires that measures be taken to avoid or mitigate any deleterious effects. Plans by the relevant authority, the North Shore City Council, are a major step forward from the unsustainable development of the neighbouring catchment. Still, more needs to be done. Ten recommendations have been made to ameliorate the potential negative impacts of the development.
5

Soft systems analysis of ecosystems

Shanmuganathan, Subana Unknown Date (has links)
This research is a case study evaluation of the use of self-organising map (SOM) techniques for ecosystem modelling to overcome the perceived inadequacies with conventional ecological data analysis methods. SOMs provide an analytical method within the connectionist paradigms of artificial neural networks (ANNs), developed from concepts that evolved from late twentieth century neuro-physiological experiments on the cortex cells of the human brain. The rate and extent at which humans influence environmental deterioration with commensurate biodiversity loss is a cause for major concern and to prevent further degradation by human impact, parsimonious models are urgently needed. Indeed, the need for better modelling techniques has never been so great. Ecologists and many national and international bodies see the situation as 'significantly critical' for the conservation of our global ecosystem to foster the continued wellbeing of humanity on this earth.The thesis investigates and further refines SOM based exploratory data analysis methods for modelling naturally evolving, highly diverse and extremely complex ecosystems. Earlier studies provide evidence on SOM ability to analyse complex forest and freshwater biological community structures at limited scales. On the other hand, growing concerns over conventional methods, their soundness and ability to model large volumes of data are seen as of little use, leading to arguments on the results derived from them. Case study chapters illustrate how SOM methods could be best applied to analyse often 'cryptic' ecosystems in a manner similar to that applied in modelling highly complex and diverse industrial system dynamics. Furthermore, SOM based data clustering methods, used for financial data analysis are investigated for integrated analysis of ecological and economic system data to study the effects of urbanisation on natural habitats.SOM approaches prove to be an excellent tool for analysing the changes within physical system variables and their effects on the biological systems analysed. The Long Bay-Okura Marine Reserve case study elaborates on how SOM based approaches could be best applied to model the reserve's intertidal zone with available numeric data. SOM maps depicted the characteristic microclimate within this zone from ecological monitoring data of physical attributes, without any geographical data being added. This kind of feature extraction from raw data is found to be useful and is applied to two more case studies to study the slow variables of ecosystems, such as population dynamics, and to establish their correlation with environmental variations. SOM maps are found to be capable of distinguishing the human induced variations from that of natural/ global variations, at different scales (site, regional and global) and levels using regional and global data. Hence, SOM approaches prove to be capable of modelling complex natural systems incorporating their spatial and temporal variations using the available monitoring data, this is a major advantage observed with SOM analyses.In the third case study, potential use of SOM techniques to analyse global trends on the effects of urbanisation in environmental and biological systems are explored using the World Bank's statistical data for different countries. Many state and international institutions, concerned over global environmental issues, have made attempts to develop indicators to assess the conditions of different ecosystems. The enhancements with SOM approaches against the currently recommended indicator system based on information pyramid and pressure-state-response (PSR) models are elaborated upon.The research results of SOM methods for ecosystem modelling, similar to that applied to industrial process modelling and financial system analysis show potential. SOM approaches (i.e. cluster, dependent component, decision system and trajectories/ time series analyses) provide a means for feature extraction from the available numeric data at different levels and scales, fulfilling the urgent need for modelling tools to conserve our global ecosystem. They can be used to bridge the gap in converting raw data into knowledge to inform sustainable ecosystem management. Increasingly, traditional methods based on Before-After-Control-Impact (BACI) designs and Analysis of Variance (ANOVA) are seen to be unsuitable for ecological data analysis, as they are unable to detect human induced environmental impacts from that of a natural cause. This thesis proves that SOM techniques could be applied to modelling not only a natural systems complexity but also its functioning and dynamics, incorporating spatial as well as temporal variations, to overcome the constraints with conventional methods as applied in other stated disciplines.
6

Soft systems analysis of ecosystems

Shanmuganathan, Subana Unknown Date (has links)
This research is a case study evaluation of the use of self-organising map (SOM) techniques for ecosystem modelling to overcome the perceived inadequacies with conventional ecological data analysis methods. SOMs provide an analytical method within the connectionist paradigms of artificial neural networks (ANNs), developed from concepts that evolved from late twentieth century neuro-physiological experiments on the cortex cells of the human brain. The rate and extent at which humans influence environmental deterioration with commensurate biodiversity loss is a cause for major concern and to prevent further degradation by human impact, parsimonious models are urgently needed. Indeed, the need for better modelling techniques has never been so great. Ecologists and many national and international bodies see the situation as 'significantly critical' for the conservation of our global ecosystem to foster the continued wellbeing of humanity on this earth.The thesis investigates and further refines SOM based exploratory data analysis methods for modelling naturally evolving, highly diverse and extremely complex ecosystems. Earlier studies provide evidence on SOM ability to analyse complex forest and freshwater biological community structures at limited scales. On the other hand, growing concerns over conventional methods, their soundness and ability to model large volumes of data are seen as of little use, leading to arguments on the results derived from them. Case study chapters illustrate how SOM methods could be best applied to analyse often 'cryptic' ecosystems in a manner similar to that applied in modelling highly complex and diverse industrial system dynamics. Furthermore, SOM based data clustering methods, used for financial data analysis are investigated for integrated analysis of ecological and economic system data to study the effects of urbanisation on natural habitats.SOM approaches prove to be an excellent tool for analysing the changes within physical system variables and their effects on the biological systems analysed. The Long Bay-Okura Marine Reserve case study elaborates on how SOM based approaches could be best applied to model the reserve's intertidal zone with available numeric data. SOM maps depicted the characteristic microclimate within this zone from ecological monitoring data of physical attributes, without any geographical data being added. This kind of feature extraction from raw data is found to be useful and is applied to two more case studies to study the slow variables of ecosystems, such as population dynamics, and to establish their correlation with environmental variations. SOM maps are found to be capable of distinguishing the human induced variations from that of natural/ global variations, at different scales (site, regional and global) and levels using regional and global data. Hence, SOM approaches prove to be capable of modelling complex natural systems incorporating their spatial and temporal variations using the available monitoring data, this is a major advantage observed with SOM analyses.In the third case study, potential use of SOM techniques to analyse global trends on the effects of urbanisation in environmental and biological systems are explored using the World Bank's statistical data for different countries. Many state and international institutions, concerned over global environmental issues, have made attempts to develop indicators to assess the conditions of different ecosystems. The enhancements with SOM approaches against the currently recommended indicator system based on information pyramid and pressure-state-response (PSR) models are elaborated upon.The research results of SOM methods for ecosystem modelling, similar to that applied to industrial process modelling and financial system analysis show potential. SOM approaches (i.e. cluster, dependent component, decision system and trajectories/ time series analyses) provide a means for feature extraction from the available numeric data at different levels and scales, fulfilling the urgent need for modelling tools to conserve our global ecosystem. They can be used to bridge the gap in converting raw data into knowledge to inform sustainable ecosystem management. Increasingly, traditional methods based on Before-After-Control-Impact (BACI) designs and Analysis of Variance (ANOVA) are seen to be unsuitable for ecological data analysis, as they are unable to detect human induced environmental impacts from that of a natural cause. This thesis proves that SOM techniques could be applied to modelling not only a natural systems complexity but also its functioning and dynamics, incorporating spatial as well as temporal variations, to overcome the constraints with conventional methods as applied in other stated disciplines.
7

Heavy metal concentrations in the Pacific oyster Crassostrea gigas

Perera, Percy Unknown Date (has links)
Heavy metals present in high concentrations in aquatic habitats are bioaccumulated within the tissues of intertidal organisms. The chemical analyses of animal tissues and sediments provide an indication of bioavailability of heavy metals in the environment. Monitoring of the coastal pollution using organisms is widely practiced all over the world.Chemical analysis of the tissues of Pacific oyster, Crassostrea gigas, and river sediments were used in this study to monitor the environmental concentrations, of cadmium, copper, lead and zinc of shallow coastal areas near to the river mouths of Mahurangi, Awaruku, Waiake, Taiorahi and Wairau. All of these river mouths are situated along the northeastern coast of Auckland. Each month, during the period of November 2002 to October 2003, three replicate samples of oysters, and sediments were collected from each of the river mouths for analysis. Three additional replicate samples of oysters were collected separately, in each month in order to calculate the condition index of oysters. Oyster tissues and sediments were analysed with Inductively Coupled Atomic Plasma Emission Spectrometer to detect the concentration levels of cadmium, copper, lead and zinc.The highest level of copper and zinc concentrations in the oyster tissues was observed in the river mouth of Wairau. Wairau river mouth receives water from heavily urbanised and industrialised catchments. A higher concentration of cadmium was observed in the oysters of the river mouth of Mahurangi than in the oysters in the other sites. The reason for this difference could be due to the heavy use of cadmium contaminated fertilizers at the pasture lands situated around the Mahurangi estuary. Therefore, the relationship between the land use of the catchments and the degree of pollution of the estuarine habitats could be established from the data obtained from this study. Higher concentrations of heavy metals were found in the sediments of Waiake, Taiorahi and Wairau compared to the sediments of Mahurangi and Awaruku. Significantly higher level of copper was observed in the sediments of Awaruku. However no clear co-relation was found between heavy metal concentration in oysters and in sediments. Variations of the condition of oysters were closely related to seasonal changes of the life cycle of the oysters. No clear relationship was found between the condition of the oysters and the heavy metal concentration of the river mouth habitats.This study provides evidence that Pacific oysters are good organisms to use as bioindicators of environmental heavy metal levels in shallow coastal waters. The results of this study suggest a clear relationship between the heavy metal concentration in river waters and the land use of the catchment areas of those rivers. The results may be useful in management strategies of the northeastern coastal areas of Auckland.
8

Reactive milling of organic compounds

Li, Ying Yu Unknown Date (has links)
Persistent organic pollutants are a well-known threat to the environment. Substances such as polycyclic aromatic hydrocarbons and chlorinated organic compounds in contaminated soil and groundwater can have severe and long-lasting effects on health in animals and humans. There is an urgent need for the development of safe technologies for their effective removal. Originally developed for mineral processing, mechanical treatment by ball milling is an extremely versatile technique for the degradation of toxic compounds. Reactive milling can rapidly destroy organic compounds without producing hazardous wastes. Complete breakdown of the organic molecules is achieved after relatively short milling times. Successful tests were conducted on polychlorobiphenyls (PCBs), DDT, DDD, DDE, Dieldrin and hexachlorobenzene with a conversion yield in the of greater than 99% (Hall et al., 1996; Monagheddu et al., 2000; Zhang et al., 2001; Zhang et al., 2002; Tanaka and Zhang, 2003; Pizzigallo et al., 2004; Nomura et al., 2005; Bellingham, 2006).In this study reactive ball milling was used to investigate the destruction of two classes of persistent organic pollutants environmental contaminants. The compounds studied are either known environmental pollutants or simple analogues. These were chosen as being representative of pollutants to investigate the pathway using ball milling destruction and in most cases were relatively small molecules so that the intermediates could be more easily identified. The first class of compounds was polycyclic aromatic compounds. Some smaller members of this class such as naphthalene, anthracene were investigated. The second class of compounds were some analogues of environmentally hazardous hydroxylated and halogenated compounds such as chloronaphthalene, bromonaphthalene, 1- naphthol, 2-naphthol and pentachlorophenol under reactive milling using GCMS analysis of the degradation pathway. Destruction efficiencies greater than 99% have been achieved for a number of organic compounds. Several different intermediates have been identified during the milling degradation. There was also some evidence from this study that halogens could be transferred between compounds during milling. The final products of the milling destruction of these compounds are an amorphous carbon residue and inorganic chloride or bromides. It was proposed that large amounts of halogens could be found however the results showed that small amounts detected. At early stages of milling a number of intermediate breakdown products were detected which were destroyed on extended milling. The core objective of this research was to clarify the reaction mechanisms pathways used of more complex polycyclic aromatic hydrocarbons and aromatic organ halogen compounds. This study is a part of a long-term research project on the destruction of toxic organic compounds by reactive milling.
9

Nutrient dynamics at Matapouri Estuary, Northern New Zealand

Soliman, Nabil Zaki Gadalla Unknown Date (has links)
Mangrove forests are an integral part of coastal wetlands in temperate and tropical regions of the world, including New Zealand. These coastal plants act as a shelter,feeding and breeding grounds for marine and terrestrial organisms. Many overseas studies have investigated the importance of mangrove and seagrass habitats in sustaining coastal food chains. In New Zealand, however, only a few studies have addressed the ecology and food web dynamics of these temperate ecosystems.As a first step to investigate the nutrient dynamics of estuarine food webs in temperate estuaries, this study aimed to quantify the nutrient concentrations in the catchment and the estuary of Matapouri, northern New Zealand. Field studies involved the collection of surface fresh and estuarine water (during low and high tides). Plant material (mangrove and seagrass), and sediment samples were collected at various sites within the estuary. Chemical analyses were carried out to determine the concentration of C, N, P and Si macronutrients and Fe and Zn micronutrients during different seasonal rainfall events.The results suggest that mangrove habitats may act as a source of POC, but not DOC for the adjacent aquatic habitats (i.e., seagrass, sand flats, channels), while seasgrass beds contribute more N to the estuarine system than the mangrove forests. The concentrations of N and P nutrients are strongly influenced by both the freshwater inputs and the bio-chemical processes within the estuary. The results obtained point to the freshwater streams as the main source of Si and Fe in the estuary. However, Zn was higher in the estuarine water compared to the catchment freshwater. NO3 -, NH4 +, Fe and Zn concentrations showed strong responses to the higher rainfall months reaching their highest level during the winter and early spring seasons. Conversely, P concentrations showed a negative seasonal pattern, which was linked to monthly rainfall events.Mangrove sediments may operate as a sink for the heavy metal Zn in Matapouri estuary. Iron concentration in seagrass leaves exceeded that in mangrove leaves by 65 orders of magnitude. The study suggests that seagrass plants could be used as a biological indicator of iron concentration in the estuary. The complex dynamics of bio-chemical cycles in Matapouri indicate that each habitat within the estuary has specific nutrient contributions to the estuarine food web system. However, the catchment and oceanic influences must also be considered in the nutrient balance of these coastal environments.
10

Heavy metal concentrations in the Pacific oyster Crassostrea gigas

Perera, Percy Unknown Date (has links)
Heavy metals present in high concentrations in aquatic habitats are bioaccumulated within the tissues of intertidal organisms. The chemical analyses of animal tissues and sediments provide an indication of bioavailability of heavy metals in the environment. Monitoring of the coastal pollution using organisms is widely practiced all over the world.Chemical analysis of the tissues of Pacific oyster, Crassostrea gigas, and river sediments were used in this study to monitor the environmental concentrations, of cadmium, copper, lead and zinc of shallow coastal areas near to the river mouths of Mahurangi, Awaruku, Waiake, Taiorahi and Wairau. All of these river mouths are situated along the northeastern coast of Auckland. Each month, during the period of November 2002 to October 2003, three replicate samples of oysters, and sediments were collected from each of the river mouths for analysis. Three additional replicate samples of oysters were collected separately, in each month in order to calculate the condition index of oysters. Oyster tissues and sediments were analysed with Inductively Coupled Atomic Plasma Emission Spectrometer to detect the concentration levels of cadmium, copper, lead and zinc.The highest level of copper and zinc concentrations in the oyster tissues was observed in the river mouth of Wairau. Wairau river mouth receives water from heavily urbanised and industrialised catchments. A higher concentration of cadmium was observed in the oysters of the river mouth of Mahurangi than in the oysters in the other sites. The reason for this difference could be due to the heavy use of cadmium contaminated fertilizers at the pasture lands situated around the Mahurangi estuary. Therefore, the relationship between the land use of the catchments and the degree of pollution of the estuarine habitats could be established from the data obtained from this study. Higher concentrations of heavy metals were found in the sediments of Waiake, Taiorahi and Wairau compared to the sediments of Mahurangi and Awaruku. Significantly higher level of copper was observed in the sediments of Awaruku. However no clear co-relation was found between heavy metal concentration in oysters and in sediments. Variations of the condition of oysters were closely related to seasonal changes of the life cycle of the oysters. No clear relationship was found between the condition of the oysters and the heavy metal concentration of the river mouth habitats.This study provides evidence that Pacific oysters are good organisms to use as bioindicators of environmental heavy metal levels in shallow coastal waters. The results of this study suggest a clear relationship between the heavy metal concentration in river waters and the land use of the catchment areas of those rivers. The results may be useful in management strategies of the northeastern coastal areas of Auckland.

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