title: The sequestration of phosphate by iron phases in the sediments from Lake Rotorua, New Zealand

authors: Mangan, Carmel Mary

subjects: sediments

abstract: A sequential extraction method was used to determine which dominant sedimentary mineral phase was involved in phosphorus retention in the sediments of Lake Rotorua and to verify the importance of iron phases in the role as a phosphorus sink. The observed influence of the experimental conditions upon the extent of phosphate adsorption to various iron phases shows a considerable quantity of phosphorus is present in the reducible phase and in the residual mineral phase. The phosphorus associated with iron(III) oxide phases was released into solution under reducing conditions when ferric iron oxide/oxyhydroxides, including amorphous and poorly crystalline Fe(III) phases, were solubilized. The residual primary and secondary mineral phases remained stable in the sediments until they were exposed to extremely acidic media analogous to strongly reducing conditions. Manganese is not involved in phosphorus retention to the same extent as iron. Aluminium phases present were released from surface complexes with relative ease and also from mineral structures under the prevailing conditions. The results show a strong agreement between aluminium and phosphorus suggesting it is associated with various aluminium phases to some extent. The sediments of Lake Rotorua are rich in organic-bound P which is released when organic material is oxidized under conditions analogous to anaerobic degradation. The degradation of refractory organic material represents a significant source of phosphorus for incorporation into diagenetic minerals forming in oxic and anoxic layers of the sediment.
Heavy liquid separation of the sediments concentrated the small quantities of dense minerals into a separate fraction and the presence of iron sulfides could be verified. Three density fractions obtained by this method separated the diatoms (d less than 2.6 g cm-3), the silicates (d greater than 2.6 less than 3.7 g cm-3) and the heavy minerals (d greater than 3.7 g cm-3) present in the sediment sample. In the heavy mineral phase spherulitic framboidal pyrite and rhombohedrial siderite were observed by scanning electron microscopy (SEM).
Energy dispersive x-ray fluorescence (XRF) analysis of the framboidal pyrite detected significant fluorescence's for sulphur and iron. The elemental analysis of siderite characterised it as an iron-rich, non-sulfidic particle with no phosphorus fluorescence. Particles were also observed that had a variable morphology to the framboidal pyrite minerals but similar ratio of Fe to S in the XRF spectrum. It is likely they are other stable forms of iron sulfides or pyrites in various stages of diagenetic dissolution. Digestion of the three density fractions shows the heavy mineral phase is significantly enriched in sulfur and in iron confirming the presence of sulfides. The sulfide-forming trace metals are concentrating in the heavy mineral phase but a progressive enrichment of trace metals down core is not found in the results. Many of the trace elements show maximum concentrations in the Tarawera tephra.
There is a good agreement between iron and phosphorus in both treatments that implies iron phases are the predominant phosphorus fixers in the sediments of Lake Rotorua. However the identity of the phosphorus sink could not be confirmed by SEM or XRF analysis of the heavy minerals. The most likely explanations for the observed concentrations of iron and phosphorus and enrichment in the heavy mineral fraction are the persistence of the highly insoluble crystalline iron oxyhydroxides (goethite) in reducing sediments or the formation of the reduced iron mineral vivianite. Considering the density of vivianite it would have being taken into the heavy fraction by default which would account for the enrichment demonstrated by the solution analysis.

text: The sequestration of phosphate by iron phases in the sediments from Lake Rotorua, New Zealand A sequential extraction method was used to determine which dominant sedimentary mineral phase was involved in phosphorus retention in the sediments of Lake Rotorua and to verify the importance of iron phases in the role as a phosphorus sink. The observed influence of the experimental conditions upon the extent of phosphate adsorption to various iron phases shows a considerable quantity of phosphorus is present in the reducible phase and in the residual mineral phase. The phosphorus associated with iron(III) oxide phases was released into solution under reducing conditions when ferric iron oxide/oxyhydroxides, including amorphous and poorly crystalline Fe(III) phases, were solubilized. The residual primary and secondary mineral phases remained stable in the sediments until they were exposed to extremely acidic media analogous to strongly reducing conditions. Manganese is not involved in phosphorus retention to the same extent as iron. Aluminium phases present were released from surface complexes with relative ease and also from mineral structures under the prevailing conditions. The results show a strong agreement between aluminium and phosphorus suggesting it is associated with various aluminium phases to some extent. The sediments of Lake Rotorua are rich in organic-bound P which is released when organic material is oxidized under conditions analogous to anaerobic degradation. The degradation of refractory organic material represents a significant source of phosphorus for incorporation into diagenetic minerals forming in oxic and anoxic layers of the sediment.
Heavy liquid separation of the sediments concentrated the small quantities of dense minerals into a separate fraction and the presence of iron sulfides could be verified. Three density fractions obtained by this method separated the diatoms (d less than 2.6 g cm-3), the silicates (d greater than 2.6 less than 3.7 g cm-3) and the heavy minerals (d greater than 3.7 g cm-3) present in the sediment sample. In the heavy mineral phase spherulitic framboidal pyrite and rhombohedrial siderite were observed by scanning electron microscopy (SEM).
Energy dispersive x-ray fluorescence (XRF) analysis of the framboidal pyrite detected significant fluorescence's for sulphur and iron. The elemental analysis of siderite characterised it as an iron-rich, non-sulfidic particle with no phosphorus fluorescence. Particles were also observed that had a variable morphology to the framboidal pyrite minerals but similar ratio of Fe to S in the XRF spectrum. It is likely they are other stable forms of iron sulfides or pyrites in various stages of diagenetic dissolution. Digestion of the three density fractions shows the heavy mineral phase is significantly enriched in sulfur and in iron confirming the presence of sulfides. The sulfide-forming trace metals are concentrating in the heavy mineral phase but a progressive enrichment of trace metals down core is not found in the results. Many of the trace elements show maximum concentrations in the Tarawera tephra.
There is a good agreement between iron and phosphorus in both treatments that implies iron phases are the predominant phosphorus fixers in the sediments of Lake Rotorua. However the identity of the phosphorus sink could not be confirmed by SEM or XRF analysis of the heavy minerals. The most likely explanations for the observed concentrations of iron and phosphorus and enrichment in the heavy mineral fraction are the persistence of the highly insoluble crystalline iron oxyhydroxides (goethite) in reducing sediments or the formation of the reduced iron mineral vivianite. Considering the density of vivianite it would have being taken into the heavy fraction by default which would account for the enrichment demonstrated by the solution analysis.

year: 2007

title: Radiocarbon age of the Kaharoa Tephra, a key marker for late-Holocene stratigraphy and archaeology in New Zealand

authors: Lowe, David J.

subjects: radiocarbon dating

abstract: The Kaharoa eruption, the most recent rhyolitic volcanic event in New Zealand, resulted in the deposition of the compositionally distinctive Kaharoa Tephra over at least 30 000 km2 of northern and eastern North Island. The tephra forms an isochronous marker bed for various late-Holocene stratigraphic and palaeoen vironmental studies but is particularly important for evaluating the chronology of New Zealand's notably short prehistory because it was erupted within the last millennium, close to the time of first Polynesian colonization. We derive a definitive radiocarbon age, previously ambiguous, for the Kaharoa Tephra of 665615 BP using cluster analysis of 22 radiocarbon ages relevant to the Kaharoa eruptive episode. The error-weighted mean age obtained on unscreened ages, minus outliers, is supported by statistically identical ages obtained from three sets of screened ages selected to minimize the effects of inbuilt age or contamination. Based on the intercepts method and 1 sigma range of Northern Hemisphere calibration curves, and after subtraction of 27 years for the interhemispheric offset, the radiocarbon age 665615 BP corresponds to calibrated dates ranging from c. 650–560 cal. BP (i.e. cal. ad 1300–1390). The approximate midpoint of this range provides a colloquial calen dar date for the Kaharoa Tephra of c. 600 cal. BP (c. cal. ad 1350).

text: Radiocarbon age of the Kaharoa Tephra, a key marker for late-Holocene stratigraphy and archaeology in New Zealand The Kaharoa eruption, the most recent rhyolitic volcanic event in New Zealand, resulted in the deposition of the compositionally distinctive Kaharoa Tephra over at least 30 000 km2 of northern and eastern North Island. The tephra forms an isochronous marker bed for various late-Holocene stratigraphic and palaeoen vironmental studies but is particularly important for evaluating the chronology of New Zealand's notably short prehistory because it was erupted within the last millennium, close to the time of first Polynesian colonization. We derive a definitive radiocarbon age, previously ambiguous, for the Kaharoa Tephra of 665615 BP using cluster analysis of 22 radiocarbon ages relevant to the Kaharoa eruptive episode. The error-weighted mean age obtained on unscreened ages, minus outliers, is supported by statistically identical ages obtained from three sets of screened ages selected to minimize the effects of inbuilt age or contamination. Based on the intercepts method and 1 sigma range of Northern Hemisphere calibration curves, and after subtraction of 27 years for the interhemispheric offset, the radiocarbon age 665615 BP corresponds to calibrated dates ranging from c. 650–560 cal. BP (i.e. cal. ad 1300–1390). The approximate midpoint of this range provides a colloquial calen dar date for the Kaharoa Tephra of c. 600 cal. BP (c. cal. ad 1350).

year: 1998

title: Ngā Tuituinga o te Pōtae: Rangatahi perspectives of leadership within Ngāti Maniapoto

authors: Moss, Luke

subjects: Rangatahi

abstract: Research on youth leadership development is often saturated by adult perceptions and thus the literature often lacks youth voice and youth perspective on what integral areas are needed for successful youth leadership development. This research focuses on the rangatahi of Ngāti Maniapoto and their perspectives of leadership within the iwi to aid the gap in academic literature relating to youth perception of leadership development.

Maniapoto has an abundance of leadership examples from the plethora of tūpuna that have developed the iwi to the leaders of contemporary Maniapoto pushing the iwi forward. The purpose of this research is to delve into the perspectives of rangatahi Maniapoto that pertain to good leadership qualities, their perception of leadership, unique leadership styles within Maniapoto, rangatahi leadership skills and perspectives of youth development within the iwi. By interviewing rangatahi with strong connection to Maniapoto this information of their perspectives revealed four integral areas of rangatahi leadership development were collated into a model for dissemination and use within the iwi for youth development practices. This model is named Ngā Tuituinga o te Pōtae and has four areas, education, collective, communication and vision. Education was identified by rangatahi as they found that learning Maniapoto reo and tikanga was integral for a Maniapoto leader, in addition they saw an opportunity to establish a wānanga to future proof our Maniapototanga. A collective approach to leadership was highlighted as the rangatahi perceive that Maniapoto leaders need to be well known in the community and have good relationships with iwi members to be successful. Rangatahi reported that communication was an important attribute for leaders to have, not just speech but communicating by doing was essential for a Maniapoto leader. Finally, rangatahi explained that leaders need to have a vision for the taiao and a vision for our people to be a successful leader, and be able to take the iwi to a place they have not been to before.

This study adds to the scarce literature on youth perceptions on youth leadership development and definitively answers the question on how rangatahi of Maniapoto perceive leadership and how rangatahi of Maniapoto would develop leadership within Te Nehenehenui. The key findings presented in this thesis indicate that rangatahi from Maniapoto engage and identify leadership in many ways, however they do agree that leadership development is necessary for Maniapoto to flourish in the future. Applying this model and research within the iwi will create new foundations for leadership to grow within Maniapoto, and fill the gap of leadership for the iwi that rangatahi have identified.

text: Ngā Tuituinga o te Pōtae: Rangatahi perspectives of leadership within Ngāti Maniapoto Research on youth leadership development is often saturated by adult perceptions and thus the literature often lacks youth voice and youth perspective on what integral areas are needed for successful youth leadership development. This research focuses on the rangatahi of Ngāti Maniapoto and their perspectives of leadership within the iwi to aid the gap in academic literature relating to youth perception of leadership development.

Maniapoto has an abundance of leadership examples from the plethora of tūpuna that have developed the iwi to the leaders of contemporary Maniapoto pushing the iwi forward. The purpose of this research is to delve into the perspectives of rangatahi Maniapoto that pertain to good leadership qualities, their perception of leadership, unique leadership styles within Maniapoto, rangatahi leadership skills and perspectives of youth development within the iwi. By interviewing rangatahi with strong connection to Maniapoto this information of their perspectives revealed four integral areas of rangatahi leadership development were collated into a model for dissemination and use within the iwi for youth development practices. This model is named Ngā Tuituinga o te Pōtae and has four areas, education, collective, communication and vision. Education was identified by rangatahi as they found that learning Maniapoto reo and tikanga was integral for a Maniapoto leader, in addition they saw an opportunity to establish a wānanga to future proof our Maniapototanga. A collective approach to leadership was highlighted as the rangatahi perceive that Maniapoto leaders need to be well known in the community and have good relationships with iwi members to be successful. Rangatahi reported that communication was an important attribute for leaders to have, not just speech but communicating by doing was essential for a Maniapoto leader. Finally, rangatahi explained that leaders need to have a vision for the taiao and a vision for our people to be a successful leader, and be able to take the iwi to a place they have not been to before.

This study adds to the scarce literature on youth perceptions on youth leadership development and definitively answers the question on how rangatahi of Maniapoto perceive leadership and how rangatahi of Maniapoto would develop leadership within Te Nehenehenui. The key findings presented in this thesis indicate that rangatahi from Maniapoto engage and identify leadership in many ways, however they do agree that leadership development is necessary for Maniapoto to flourish in the future. Applying this model and research within the iwi will create new foundations for leadership to grow within Maniapoto, and fill the gap of leadership for the iwi that rangatahi have identified.

year: 2021