title: Effects of lake trophic state and seasonal cycling on production and bioaccumulation of methylmercury in Te Arawa Lakes

authors: Chong, Grace-Lynn

abstract: There are natural sources of Mercury in New Zealand, primarily derived from volcanic activity and geothermal vents. Mercury (Hg) and its organic derivative, methylmercury (MeHg), are highly toxic to both the environment and human health. Of particular concern is the ability of MeHg to bioaccumulate in aquatic food webs, leading to increased toxicity in higher trophic organisms. Given that fish constitute a significant component of the local diet, comprehensive monitoring of Hg and MeHg concentrations is essential for developing effective mitigation strategies. Such efforts are critical to controlling Hg contamination in the environment and aquatic biota, as well as informing the public about lakes with elevated mercury levels. Previous Hg studies in New Zealand have been limited in scope, with monitoring efforts focused on only a few lakes rather than a comprehensive assessment across multiple ecosystems. Additionally, most existing research has primarily examined elemental Hg, with limited investigation into the distribution and bioavailability of MeHg.   

This study aims to comprehensively assess Hg and MeHg concentrations in 11 lakes of the Taupo Volcanic Zone. The study assessed Hg and MeHg concentrations in lake water and aquatic biota, including trout, crayfish (koura), and mussels (kakahi). To achieve this, Hg and MeHg in the water were measured using diffusive gradients in thin films (DGT) samplers, while tissue analyses determined Hg, MeHg and additional trace elements in the selected species. The findings of this study are expected to clarify the distribution and bioaccumulation of Hg and MeHg within lake ecosystems and to elucidate their transfer through the aquatic food web. These results will provide a scientific basis for assessing ecological and human health risks associated with mercury exposure, particularly for culturally and recreationally important species. The outcomes will inform lake management and monitoring strategies by identifying key pathways of mercury uptake and potential bioindicator species, and may guide the development of targeted mitigation measures, such as catchment management or advisories on species consumption. Collectively, this research will support evidence-based decision-making for freshwater ecosystem protection and long-term contaminant management.  

The results of this study revealed that total mercury (THg) and MeHg concentrations in trout, koura, and kakahi from Lakes Rotorua, Rotoiti, and Rotomahana exceeded WHO recommended safety thresholds. This study also found that a substantial proportion of THg was comprised of MeHg, which was predominantly accumulated in muscle tissue, whereas THg was primarily concentrated in the liver. The findings further indicated that eutrophication, lake stratification and hypolimnetic anoxia contribute to the enhanced production and bioaccumulation of Hg and MeHg within these aquatic systems. Additionally, selenium (Se) demonstrated a potential protective effect against MeHg toxicity in aquatic organisms.

text: Effects of lake trophic state and seasonal cycling on production and bioaccumulation of methylmercury in Te Arawa Lakes There are natural sources of Mercury in New Zealand, primarily derived from volcanic activity and geothermal vents. Mercury (Hg) and its organic derivative, methylmercury (MeHg), are highly toxic to both the environment and human health. Of particular concern is the ability of MeHg to bioaccumulate in aquatic food webs, leading to increased toxicity in higher trophic organisms. Given that fish constitute a significant component of the local diet, comprehensive monitoring of Hg and MeHg concentrations is essential for developing effective mitigation strategies. Such efforts are critical to controlling Hg contamination in the environment and aquatic biota, as well as informing the public about lakes with elevated mercury levels. Previous Hg studies in New Zealand have been limited in scope, with monitoring efforts focused on only a few lakes rather than a comprehensive assessment across multiple ecosystems. Additionally, most existing research has primarily examined elemental Hg, with limited investigation into the distribution and bioavailability of MeHg.   

This study aims to comprehensively assess Hg and MeHg concentrations in 11 lakes of the Taupo Volcanic Zone. The study assessed Hg and MeHg concentrations in lake water and aquatic biota, including trout, crayfish (koura), and mussels (kakahi). To achieve this, Hg and MeHg in the water were measured using diffusive gradients in thin films (DGT) samplers, while tissue analyses determined Hg, MeHg and additional trace elements in the selected species. The findings of this study are expected to clarify the distribution and bioaccumulation of Hg and MeHg within lake ecosystems and to elucidate their transfer through the aquatic food web. These results will provide a scientific basis for assessing ecological and human health risks associated with mercury exposure, particularly for culturally and recreationally important species. The outcomes will inform lake management and monitoring strategies by identifying key pathways of mercury uptake and potential bioindicator species, and may guide the development of targeted mitigation measures, such as catchment management or advisories on species consumption. Collectively, this research will support evidence-based decision-making for freshwater ecosystem protection and long-term contaminant management.  

The results of this study revealed that total mercury (THg) and MeHg concentrations in trout, koura, and kakahi from Lakes Rotorua, Rotoiti, and Rotomahana exceeded WHO recommended safety thresholds. This study also found that a substantial proportion of THg was comprised of MeHg, which was predominantly accumulated in muscle tissue, whereas THg was primarily concentrated in the liver. The findings further indicated that eutrophication, lake stratification and hypolimnetic anoxia contribute to the enhanced production and bioaccumulation of Hg and MeHg within these aquatic systems. Additionally, selenium (Se) demonstrated a potential protective effect against MeHg toxicity in aquatic organisms.

year: 2025

title: Maori women and dual ethnicity: Non-congruence, “passing” and “real Maori”

authors: Gibson, Kelly

subjects: Maori

abstract: In this study, I wanted to explore the often uncomfortable experience of having dual ethnicity. I did
this through open-ended interviews with nine women, who, like me, were aged between 20 and 30
and who identified as being of both Maori and Pakeha (or other) descent.
While the women all identified as having dual ethnicity, as the interviews progressed it became
clear that many of them had little pride in being of Pakeha descent and identified more strongly
with their Maori heritage. In most instances the way they were identified by other people was
incongruent with how the participants identified themselves. By virtue of having fair skin, many
were able to “pass” as Pakeha. This provided them with certain advantages, notably being exempt
from racist treatment. On the other hand, their appearance often resulted in them being labelled as
not being a “real Maori.” Paradoxically, when they were identified as Maori, others, both Maori
and non-Maori, sometimes expected them to be an expert in all things Maori. For most participants
being a “real” Maori did not rely on looking Maori or on being able to speak Te Reo fluently.
Instead, having whakapapa was considered the most essential element on which to base their Maori
identity.

text: Maori women and dual ethnicity: Non-congruence, “passing” and “real Maori” In this study, I wanted to explore the often uncomfortable experience of having dual ethnicity. I did
this through open-ended interviews with nine women, who, like me, were aged between 20 and 30
and who identified as being of both Maori and Pakeha (or other) descent.
While the women all identified as having dual ethnicity, as the interviews progressed it became
clear that many of them had little pride in being of Pakeha descent and identified more strongly
with their Maori heritage. In most instances the way they were identified by other people was
incongruent with how the participants identified themselves. By virtue of having fair skin, many
were able to “pass” as Pakeha. This provided them with certain advantages, notably being exempt
from racist treatment. On the other hand, their appearance often resulted in them being labelled as
not being a “real Maori.” Paradoxically, when they were identified as Maori, others, both Maori
and non-Maori, sometimes expected them to be an expert in all things Maori. For most participants
being a “real” Maori did not rely on looking Maori or on being able to speak Te Reo fluently.
Instead, having whakapapa was considered the most essential element on which to base their Maori
identity.

year: 1999

title: Non-destructive evaluation of additively manufactured materials: developing a coupled acoustic emission and thermoelastic stress analysis approach

authors: Jouan, Denis

abstract: A method combining two non-destructive evaluations techniques, acoustic emission and thermoelastic stress analysis, is proposed to monitor cyclically loaded monolithic and additive manufactured metallic samples for crack growth. Current literature was used to investigate additive manufacturing processes and their current quality control methods. A review of acoustic emission and thermoelastic stress analysis theory and recent applications is also provided. It was found that there was currently a gap in monitoring methods for additive manufactured parts under fatigue loading for crack growth due to internal defects. Acoustic emission and thermoelastic stress analysis have never been combined to monitor crack growth in monolithic or additive manufactured metals in such a way and would be ideal methods for crack growth monitoring under cyclic loading due to their inherent benefits. Thermoelastic stress analysis is a full-field non-contact non-destructive evaluation technique which can monitor surface stress fields in materials subjected to cyclic loading. Acoustic emission is ideal for monitoring fatigue damage due to its continuous monitoring capabilities of energy released by crack growth. The proposed method consisted of acoustic emission capturing continuously and saving any waveforms exceeding a set threshold while the thermoelastic stress analysis captured data at regular intervals. Acoustic emission energy was extracted from captured waveforms to provide crack initiation detection as well as a measure of crack severity. Thermoelastic stress analysis provided a crack tip location and enabled crack tip tracking as well as crack growth rate monitoring to complement the acoustic emission energy findings. Acoustic emission could not locate the crack because it only used a single piezoelectric sensor but could detect crack growth anywhere on the sample while thermoelastic stress analysis could give the crack location only if the crack was near the surface or within the field of observation. The method successfully detected cracks and tracked crack growth in monolithic aluminium samples, additive manufactured aluminium and additive manufactured titanium alloy samples under fatigue loading conditions. This method involves little modification to the part being observed, the surface must be painted with a thin coat of matt black paint for thermoelastic stress analysis, and a sensor must be attached to the part for acoustic emission. Acoustic emission energy detected crack growth before thermoelastic stress analysis in most tests however this was due to the experimental method, acoustic emission captures continuously while thermoelastic stress analysis is at regular time intervals. Issues with experimental method came to light in early tests but were addressed in the final tests using additive manufactured titanium samples. Future work includes testing additive manufactured samples with built-in subsurface defects and developing a chip-based system in order to make a smaller and cheaper monitoring system.

text: Non-destructive evaluation of additively manufactured materials: developing a coupled acoustic emission and thermoelastic stress analysis approach A method combining two non-destructive evaluations techniques, acoustic emission and thermoelastic stress analysis, is proposed to monitor cyclically loaded monolithic and additive manufactured metallic samples for crack growth. Current literature was used to investigate additive manufacturing processes and their current quality control methods. A review of acoustic emission and thermoelastic stress analysis theory and recent applications is also provided. It was found that there was currently a gap in monitoring methods for additive manufactured parts under fatigue loading for crack growth due to internal defects. Acoustic emission and thermoelastic stress analysis have never been combined to monitor crack growth in monolithic or additive manufactured metals in such a way and would be ideal methods for crack growth monitoring under cyclic loading due to their inherent benefits. Thermoelastic stress analysis is a full-field non-contact non-destructive evaluation technique which can monitor surface stress fields in materials subjected to cyclic loading. Acoustic emission is ideal for monitoring fatigue damage due to its continuous monitoring capabilities of energy released by crack growth. The proposed method consisted of acoustic emission capturing continuously and saving any waveforms exceeding a set threshold while the thermoelastic stress analysis captured data at regular intervals. Acoustic emission energy was extracted from captured waveforms to provide crack initiation detection as well as a measure of crack severity. Thermoelastic stress analysis provided a crack tip location and enabled crack tip tracking as well as crack growth rate monitoring to complement the acoustic emission energy findings. Acoustic emission could not locate the crack because it only used a single piezoelectric sensor but could detect crack growth anywhere on the sample while thermoelastic stress analysis could give the crack location only if the crack was near the surface or within the field of observation. The method successfully detected cracks and tracked crack growth in monolithic aluminium samples, additive manufactured aluminium and additive manufactured titanium alloy samples under fatigue loading conditions. This method involves little modification to the part being observed, the surface must be painted with a thin coat of matt black paint for thermoelastic stress analysis, and a sensor must be attached to the part for acoustic emission. Acoustic emission energy detected crack growth before thermoelastic stress analysis in most tests however this was due to the experimental method, acoustic emission captures continuously while thermoelastic stress analysis is at regular time intervals. Issues with experimental method came to light in early tests but were addressed in the final tests using additive manufactured titanium samples. Future work includes testing additive manufactured samples with built-in subsurface defects and developing a chip-based system in order to make a smaller and cheaper monitoring system.

year: 2022