title: Redox cycling of colloidal macro- and micro-nutrients in a monomictic lake

authors: Saeed, Huma

subjects: Anoxia

abstract: Lakes are more than just water bodies as they play an essential role in the cycling of nutrients and carbon, with impacts at the local and global scale. This study selected Lake Ngapouri, a small monomictic lake in the Waikiti Valley, Taupo Volcanic Zone, New Zealand, which receives a considerable amount of nutrients and organic carbon input from the surrounding pastures. The study was designed to investigate the cycling of nutrients and dissolved organic carbon in lake Ngapouri, with a focus on processes occurring at the colloidal size level under varying thermal and redox conditions. 
To achieve the objectives of the study, a year-long sampling campaign was designed involving field and laboratory measurements of the lake's water column. The lake's physicochemical characteristics were determined via high-resolution depth profiles and paried  with a detailed set of depth-resolved geochemical measurements. Analysis for reduced Fe (II) was used to control for oxidative loss during transportation and storage of samples, and generally demonstrated very good protocols and minimal sample alteration. 
This work comprises a comparison of components in colloidal and dissolved size ranges, determined by ultrafiltration under a zero grade N2 atmosphere, and in situ measurements by diffusive gradients in thin films (DGT). Colloids from the lake were additionally analyzed using transmission electron microscopy (TEM), atomic force microscopy (AFM), fluorescence spectroscopy, and a suite of complementary methods. 
Results show considerable changes in the physicochemical properties of the lake over the hydrological year. Isothermal conditions prevailed through the water column during austral autumn and winter, with thermal stratification becoming established as the summer progressed. Dissolved oxygen concentration followed the thermal pattern, and thus vertically divided the water column into three distinct zones during summer. These zones are referred to as 1) Epilimnion (0-5m measuring from the surface) with uniform thermal and dissolved oxygen concentration, 2) transition zone with varying temperature and dissolved oxygen concentration referred to as metalimnion (6-13m), and 3) hypolimnion (15-20m) marked with cold water and reduced oxygen concentration in comparison to the upper two compartments. The pH of the water column stayed circumneutral during this study. The implications of the lake's variation in thermal and redox status on the cycling of macro and micronutrients are discussed in data chapters.  
The third chapter of this thesis addresses the role of suspended iron hydroxides in phosphorus cycling. The spatial and temporal distribution of iron and phosphorus was clearly coupled and was strongly influenced by sediment releases of both elements in anaerobic bed sediments. Both iron and phosphorus were predominantly colloidal and displayed an increasing degree of lability (to DGT) as hypolimnetic anoxia deepened. The implications of this finding are that iron-based colloids can mediate phosphorus cycling even under anaerobic conditions, and might therefore influence iron and phosphorus bioavailability within the water column. 
The fourth chapter of this thesis explores the evolution, seasonal production, and consumption of dissolved organic matter (DOM) in the water column of Lake Ngapouri. Both the quality and quantity of DOM influence the turnover of DOM in the lake system, and this influence was explored using the constituent molecules' fluorescent properties. The resulting excitation-emission matrices (EEM's) were analyzed using parallel factor analysis (PARAFAC), identifying two humic-like fluorophores and one protein-like fluorophore in both colloidal and dissolved size fractions. DOM in the lake showed marked seasonality with greater production and turnover during the summer season. This study shows that the concentration of humic-like DOM was ~3.5 times lower and less variable than protein-like DOM. The proteinaceous material in the low molecular weight fraction cycled actively in the anaerobic hypolimnetic water during summer, consistent with the contemporaneous dissimilatory reduction of manganese, iron, and sulphur. 
Chapter 5 of this thesis examines the spatial and temporal distribution of trace elements (iron (Fe), manganese (Mn), zinc (Zn), copper(Cu), chromium (Cr), cobalt (Co), nickel (Ni), and cadmium (Cd)) in Lake Ngapouri, and the degree to which binding to colloidal surfaces and DOM influence trace element bioavailability. DGT-lability was thus used as a proxy the available metal for biological uptake. In general, the DGT-labile fraction was much lower than a total load of respective trace metal, indicating the significance of adsorption, precipitation, and complexation reactions for trace metal availability for biological uptake. Broadly, the study groups trace metals into two distinct categories: strongly redox cycled, and controlled by organic complexation. This work shows that colloidal association is often, but not always a predictor of lower bioavailability with important implications for our understanding of metal micronutrients in aquatic systems. 
The contributions from this study are significant for studies of the bioavailability of macro and micronutrients which exhibit strong adsorption behavior. The redox state of lakes affects the formation, complexation character, and stability of various mineral colloids. Colloids clearly should be considered as an important intermediary phase with the potential to affect nutrient availability and with implications for lake restoration and management initiatives.

text: Redox cycling of colloidal macro- and micro-nutrients in a monomictic lake Lakes are more than just water bodies as they play an essential role in the cycling of nutrients and carbon, with impacts at the local and global scale. This study selected Lake Ngapouri, a small monomictic lake in the Waikiti Valley, Taupo Volcanic Zone, New Zealand, which receives a considerable amount of nutrients and organic carbon input from the surrounding pastures. The study was designed to investigate the cycling of nutrients and dissolved organic carbon in lake Ngapouri, with a focus on processes occurring at the colloidal size level under varying thermal and redox conditions. 
To achieve the objectives of the study, a year-long sampling campaign was designed involving field and laboratory measurements of the lake's water column. The lake's physicochemical characteristics were determined via high-resolution depth profiles and paried  with a detailed set of depth-resolved geochemical measurements. Analysis for reduced Fe (II) was used to control for oxidative loss during transportation and storage of samples, and generally demonstrated very good protocols and minimal sample alteration. 
This work comprises a comparison of components in colloidal and dissolved size ranges, determined by ultrafiltration under a zero grade N2 atmosphere, and in situ measurements by diffusive gradients in thin films (DGT). Colloids from the lake were additionally analyzed using transmission electron microscopy (TEM), atomic force microscopy (AFM), fluorescence spectroscopy, and a suite of complementary methods. 
Results show considerable changes in the physicochemical properties of the lake over the hydrological year. Isothermal conditions prevailed through the water column during austral autumn and winter, with thermal stratification becoming established as the summer progressed. Dissolved oxygen concentration followed the thermal pattern, and thus vertically divided the water column into three distinct zones during summer. These zones are referred to as 1) Epilimnion (0-5m measuring from the surface) with uniform thermal and dissolved oxygen concentration, 2) transition zone with varying temperature and dissolved oxygen concentration referred to as metalimnion (6-13m), and 3) hypolimnion (15-20m) marked with cold water and reduced oxygen concentration in comparison to the upper two compartments. The pH of the water column stayed circumneutral during this study. The implications of the lake's variation in thermal and redox status on the cycling of macro and micronutrients are discussed in data chapters.  
The third chapter of this thesis addresses the role of suspended iron hydroxides in phosphorus cycling. The spatial and temporal distribution of iron and phosphorus was clearly coupled and was strongly influenced by sediment releases of both elements in anaerobic bed sediments. Both iron and phosphorus were predominantly colloidal and displayed an increasing degree of lability (to DGT) as hypolimnetic anoxia deepened. The implications of this finding are that iron-based colloids can mediate phosphorus cycling even under anaerobic conditions, and might therefore influence iron and phosphorus bioavailability within the water column. 
The fourth chapter of this thesis explores the evolution, seasonal production, and consumption of dissolved organic matter (DOM) in the water column of Lake Ngapouri. Both the quality and quantity of DOM influence the turnover of DOM in the lake system, and this influence was explored using the constituent molecules' fluorescent properties. The resulting excitation-emission matrices (EEM's) were analyzed using parallel factor analysis (PARAFAC), identifying two humic-like fluorophores and one protein-like fluorophore in both colloidal and dissolved size fractions. DOM in the lake showed marked seasonality with greater production and turnover during the summer season. This study shows that the concentration of humic-like DOM was ~3.5 times lower and less variable than protein-like DOM. The proteinaceous material in the low molecular weight fraction cycled actively in the anaerobic hypolimnetic water during summer, consistent with the contemporaneous dissimilatory reduction of manganese, iron, and sulphur. 
Chapter 5 of this thesis examines the spatial and temporal distribution of trace elements (iron (Fe), manganese (Mn), zinc (Zn), copper(Cu), chromium (Cr), cobalt (Co), nickel (Ni), and cadmium (Cd)) in Lake Ngapouri, and the degree to which binding to colloidal surfaces and DOM influence trace element bioavailability. DGT-lability was thus used as a proxy the available metal for biological uptake. In general, the DGT-labile fraction was much lower than a total load of respective trace metal, indicating the significance of adsorption, precipitation, and complexation reactions for trace metal availability for biological uptake. Broadly, the study groups trace metals into two distinct categories: strongly redox cycled, and controlled by organic complexation. This work shows that colloidal association is often, but not always a predictor of lower bioavailability with important implications for our understanding of metal micronutrients in aquatic systems. 
The contributions from this study are significant for studies of the bioavailability of macro and micronutrients which exhibit strong adsorption behavior. The redox state of lakes affects the formation, complexation character, and stability of various mineral colloids. Colloids clearly should be considered as an important intermediary phase with the potential to affect nutrient availability and with implications for lake restoration and management initiatives.

year: 2022

title: Encouraging better hand drying hygiene

authors: Cunningham, Sally Jo

subjects: computer science

abstract: Electric hand driers have the potential to improve sanitation when using public toilets; if used properly, electric driers can dry hands more thoroughly than towels, and users do not come into physical contact with potentially contaminated objects. But electric driers are frequently used for just a few seconds--and so the potential advantage is lost. This paper describes the prototyping and evaluation of a system intended to encourage longer hand drying times in public toilets. The challenges are: to develop hygienic interfaces for use in toilet areas; to design simple to use software that is engaging enough to be used several times a day; and to conduct usability and system acceptance tests in an environment in which users are highly sensitive about privacy issues.

text: Encouraging better hand drying hygiene Electric hand driers have the potential to improve sanitation when using public toilets; if used properly, electric driers can dry hands more thoroughly than towels, and users do not come into physical contact with potentially contaminated objects. But electric driers are frequently used for just a few seconds--and so the potential advantage is lost. This paper describes the prototyping and evaluation of a system intended to encourage longer hand drying times in public toilets. The challenges are: to develop hygienic interfaces for use in toilet areas; to design simple to use software that is engaging enough to be used several times a day; and to conduct usability and system acceptance tests in an environment in which users are highly sensitive about privacy issues.

year: 2008

title: Mahi Toi Skills in Contemporary Education, Training and Maori Development

authors: Joseph, Makarita Ngapine Tangitu

subjects: Kia mau ki nga taonga tuku iho o nga tupuna

abstract: Since the 1980’s, national investment in human capital and skill formation policy in education has been promoted as key to economic success and social inclusion. Social inclusion, however, is often expressed as helping citizens to become employable. Although employability is a key focus of skills formation and education policy, the context of the western ideologies that it derives from and caters to perpetuates the exclusion of mahi toi (arts and crafts) skills in education. Using a kaupapa Māori approach, two key informants who specialise and teach mahi toi skills, either rāranga (weaving) or pounamu (jade/greenstone), were interviewed. The aim was to get a better understanding of how these skills can contribute to personal, professional and Māori development in the 21st century, and to provide information indicating where and how these skills can be learnt, either through private training enterprises (PTE) or public tertiary educational institutions (TEI), thereby highlighting the value of teaching and learning rāranga and pounamu skills. Findings from analysing their pūrākau indicate that learning rāranga or pounamu skills can provide a foundation for believing in your potential, contribute to cultural identity, improve confidence and communication skills, help an individual be bestowed or acquire mana, offer a type of therapy, enhance career progression and professional identity, provide financial rewards and stability, and help with the revitalisation and transfer of cultural knowledge. Ultimately, it is concluded that mahi toi skills such as rāranga and pounamu can contribute to the development of an individual’s personal and professional lives, but also has benefits for the organisation where they become employed as well as extended whānau, hapū and iwi.

text: Mahi Toi Skills in Contemporary Education, Training and Maori Development Since the 1980’s, national investment in human capital and skill formation policy in education has been promoted as key to economic success and social inclusion. Social inclusion, however, is often expressed as helping citizens to become employable. Although employability is a key focus of skills formation and education policy, the context of the western ideologies that it derives from and caters to perpetuates the exclusion of mahi toi (arts and crafts) skills in education. Using a kaupapa Māori approach, two key informants who specialise and teach mahi toi skills, either rāranga (weaving) or pounamu (jade/greenstone), were interviewed. The aim was to get a better understanding of how these skills can contribute to personal, professional and Māori development in the 21st century, and to provide information indicating where and how these skills can be learnt, either through private training enterprises (PTE) or public tertiary educational institutions (TEI), thereby highlighting the value of teaching and learning rāranga and pounamu skills. Findings from analysing their pūrākau indicate that learning rāranga or pounamu skills can provide a foundation for believing in your potential, contribute to cultural identity, improve confidence and communication skills, help an individual be bestowed or acquire mana, offer a type of therapy, enhance career progression and professional identity, provide financial rewards and stability, and help with the revitalisation and transfer of cultural knowledge. Ultimately, it is concluded that mahi toi skills such as rāranga and pounamu can contribute to the development of an individual’s personal and professional lives, but also has benefits for the organisation where they become employed as well as extended whānau, hapū and iwi.

year: 2018