Ling, NicholasChong, Grace-Lynn2026-02-222026-02-222025https://hdl.handle.net/10289/17950There 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.enAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.Thesis