title: Nitrogen Isotope Variation in the Environment:  Implications for Interpretation

authors: Tozer, Wade Colin

subjects: d15N

abstract: Natural abundance of 15N varies greatly and unpredictably within and between environments.  The unpredictable nature of 15N limits the use of N isotope natural abundance (d15N) in tracing the flow and fate of N in environments.  Recent investigations have, however, revealed consistent and repeatable patterns of 15N in some ecosystem components.  These patterns suggest that d15N may yet provide a tool to investigate and illuminate ecosystem N cycling processes.  Identifying and quantifying the sources of isotopic variation must precede any significant advance in the application of this technique, and to this end an assessment of isotopic variation associated with major ecosystem components has been carried out in this thesis.  d15N patterns have been established, hypotheses proposed and tested, and conclusions about the application of the technique are presented.

15N patterns in surface and groundwater were measured in a variety of different land-use catchments in an attempt to identify distinct isotopic 'fingerprints'.  High levels of 15N variation were measured in both stream and groundwaters, resulting in strongly overlapping land-use 'fingerprints'.  Environmental 15N variation in streams and groundwaters was found to be too great to differentiate between land-uses based on d15N alone.

In contrast, the artificially 15N enriched signature of effluent N was used to trace its flow and fate, following irrigation, in a forested catchment.  The effluent d15N signature allowed it to be traced into the major ecosystem components, permitting a first order N budget to be determined for effluent N storage and loss.  N sources with significantly different 15N signatures to that of 'background ecosystem N' can therefore be used to trace the flow and fate of N in ecosystems.

During the course of this work a number of higher and lower order plants were observed to have highly depleted (lt; -8 ) d15N signatures.  Epiphytes and lithophytes, strongly reliant on atmospheric N sources, were consistently depleted in 15N, with signatures as low as -24 , measured in a range of environments.  A similar level of depletion was measured in a wide range of plants growing in early primary succession sites (as low as -22.3 ), which could not be accounted for by any abiotic or biotic factor or significantly depleted N source.  The absence of any measurable driver of depletion suggested a universal fractionating mechanism which acts in a wide range of environments and vegetation types.  Diffusive uptake of atmospheric NH3(g) and the proportional uptake of a supplied N source were two proposed mechanisms that could theoretically account for the level and universal nature of depletion. 

Diffusive uptake of atmospheric NH3(g) was tested as a primary fractionating mechanism in plants.  Strongly N deficient plants were capable of utilising NH3(g) as a nutritional source, but the level of 15N depletion measured in these plants closely approximated that of the inherent NH3(g) d15N signature.  No significant additional fractionation is associated with NH3(g) diffusive uptake.  Diffusive uptake of atmospheric NH3(g) by plants cannot alone account for the level of depletion measured in early primary succession plant communities. 

Proportional uptake of a N source as a primary fractionating mechanism was tested by growing plants in various concentrations and rates of applied N.  Fractionation attributed to the proportional uptake of a supplied N source, as a consequence of P limitation or rapid flow over roots, resulted in a significant level of 15N depletion in plants. The level of depletion attributed to this mechanism was, however, not sufficient to account for the level measured in early primary succession plant communities.

Individual 15N fractionating mechanisms cannot alone explain the level of depletion observed in early primary succession plants, however a combination of fractionating mechanisms can.  Fractionation attributed to the proportional uptake of an already depleted N source, i.e., wet deposited N, largely accounts for the level of depletion measured in early succession plant communities.  This two-step fractionation model can act on both higher and lower plants, independent of ecosystem biotic and abiotic factors.  Additional, and less dramatic fractionations attributed to atmospheric NH3(g) uptake, mycorrhizal associations, internal remobilisation, and taxon-specific N acquisition strategies, will contribute to the level of d15N depletion.  
This thesis presents the first extensive survey of highly depleted d15N signatures in terrestrial vegetation.  Furthermore, thorough testing of theoretically plausible mechanisms has resulted in a full account of the highly depleted d15N signatures measured in a wide range of vegetation types and environments.

text: Nitrogen Isotope Variation in the Environment:  Implications for Interpretation Natural abundance of 15N varies greatly and unpredictably within and between environments.  The unpredictable nature of 15N limits the use of N isotope natural abundance (d15N) in tracing the flow and fate of N in environments.  Recent investigations have, however, revealed consistent and repeatable patterns of 15N in some ecosystem components.  These patterns suggest that d15N may yet provide a tool to investigate and illuminate ecosystem N cycling processes.  Identifying and quantifying the sources of isotopic variation must precede any significant advance in the application of this technique, and to this end an assessment of isotopic variation associated with major ecosystem components has been carried out in this thesis.  d15N patterns have been established, hypotheses proposed and tested, and conclusions about the application of the technique are presented.

15N patterns in surface and groundwater were measured in a variety of different land-use catchments in an attempt to identify distinct isotopic 'fingerprints'.  High levels of 15N variation were measured in both stream and groundwaters, resulting in strongly overlapping land-use 'fingerprints'.  Environmental 15N variation in streams and groundwaters was found to be too great to differentiate between land-uses based on d15N alone.

In contrast, the artificially 15N enriched signature of effluent N was used to trace its flow and fate, following irrigation, in a forested catchment.  The effluent d15N signature allowed it to be traced into the major ecosystem components, permitting a first order N budget to be determined for effluent N storage and loss.  N sources with significantly different 15N signatures to that of 'background ecosystem N' can therefore be used to trace the flow and fate of N in ecosystems.

During the course of this work a number of higher and lower order plants were observed to have highly depleted (lt; -8 ) d15N signatures.  Epiphytes and lithophytes, strongly reliant on atmospheric N sources, were consistently depleted in 15N, with signatures as low as -24 , measured in a range of environments.  A similar level of depletion was measured in a wide range of plants growing in early primary succession sites (as low as -22.3 ), which could not be accounted for by any abiotic or biotic factor or significantly depleted N source.  The absence of any measurable driver of depletion suggested a universal fractionating mechanism which acts in a wide range of environments and vegetation types.  Diffusive uptake of atmospheric NH3(g) and the proportional uptake of a supplied N source were two proposed mechanisms that could theoretically account for the level and universal nature of depletion. 

Diffusive uptake of atmospheric NH3(g) was tested as a primary fractionating mechanism in plants.  Strongly N deficient plants were capable of utilising NH3(g) as a nutritional source, but the level of 15N depletion measured in these plants closely approximated that of the inherent NH3(g) d15N signature.  No significant additional fractionation is associated with NH3(g) diffusive uptake.  Diffusive uptake of atmospheric NH3(g) by plants cannot alone account for the level of depletion measured in early primary succession plant communities. 

Proportional uptake of a N source as a primary fractionating mechanism was tested by growing plants in various concentrations and rates of applied N.  Fractionation attributed to the proportional uptake of a supplied N source, as a consequence of P limitation or rapid flow over roots, resulted in a significant level of 15N depletion in plants. The level of depletion attributed to this mechanism was, however, not sufficient to account for the level measured in early primary succession plant communities.

Individual 15N fractionating mechanisms cannot alone explain the level of depletion observed in early primary succession plants, however a combination of fractionating mechanisms can.  Fractionation attributed to the proportional uptake of an already depleted N source, i.e., wet deposited N, largely accounts for the level of depletion measured in early succession plant communities.  This two-step fractionation model can act on both higher and lower plants, independent of ecosystem biotic and abiotic factors.  Additional, and less dramatic fractionations attributed to atmospheric NH3(g) uptake, mycorrhizal associations, internal remobilisation, and taxon-specific N acquisition strategies, will contribute to the level of d15N depletion.  
This thesis presents the first extensive survey of highly depleted d15N signatures in terrestrial vegetation.  Furthermore, thorough testing of theoretically plausible mechanisms has resulted in a full account of the highly depleted d15N signatures measured in a wide range of vegetation types and environments.

year: 2006

title: On ensemble techniques for data stream regression

authors: Gomes, Heitor Murilo

subjects: Science & Technology

abstract: An ensemble of learners tends to exceed the predictive performance of individual learners. This approach has been explored for both batch and online learning. Ensembles methods applied to data stream classification were thoroughly investigated over the years, while their regression counterparts received less attention in comparison. In this work, we discuss and analyze several techniques for generating, aggregating, and updating ensembles of regressors for evolving data streams. We investigate the impact of different strategies for inducing diversity into the ensemble by randomizing the input data (resampling, random subspaces and random patches). On top of that, we devote particular attention to techniques that adapt the ensemble model in response to concept drifts, including adaptive window approaches, fixed periodical resets and randomly determined windows. Extensive empirical experiments show that simple techniques can obtain similar predictive performance to sophisticated algorithms that rely on reactive adaptation (i.e., concept drift detection and recovery).

text: On ensemble techniques for data stream regression An ensemble of learners tends to exceed the predictive performance of individual learners. This approach has been explored for both batch and online learning. Ensembles methods applied to data stream classification were thoroughly investigated over the years, while their regression counterparts received less attention in comparison. In this work, we discuss and analyze several techniques for generating, aggregating, and updating ensembles of regressors for evolving data streams. We investigate the impact of different strategies for inducing diversity into the ensemble by randomizing the input data (resampling, random subspaces and random patches). On top of that, we devote particular attention to techniques that adapt the ensemble model in response to concept drifts, including adaptive window approaches, fixed periodical resets and randomly determined windows. Extensive empirical experiments show that simple techniques can obtain similar predictive performance to sophisticated algorithms that rely on reactive adaptation (i.e., concept drift detection and recovery).

year: 2020

title: Proposing a Kaupapa Tuku Iho informed Māori model for practice to enhance cultural competence and foster kaimahi flourishing within health and social service providers

authors: Winiata, Rangimarie

subjects: Kaupapa Tuku Iho

abstract: Kaupapa Tuku Iho are Māori values that have been used across various social institutions to inform culturally competent practices with those accessing services. This thesis set out to promote the use Kaupapa Tuku Iho to not only enhance cultural competence and culturally appropriate services, but to take a step further and explore factors that foster the flourishing of kaimahi (workers) who deliver those services. There is research that suggests kaimahi in health and social services are overworked, burdened by stressed and approaching a state of compassion fatigue. This is detrimental for those both delivering and accessing services. This study will explore factors that foster kaimahi flourishing and enable kaimahi to practice Kaupapa Tuku Iho, along with factors that stand as barriers to achieving flourishing and culturally competent practice.
Furthermore, I have developed Ngā Kākano, which is a values-based model informed by Kaupapa Tuku Iho that aims to foster kaimahi flourishing and achieve culturally competent practice within health and social service providers. Ngā Kākano has been aligned to various psychological disciplines, including Community Psychology, Industrial-Organisational Psychology and Indigenous Psychology.
Data concerning the exploration of barriers and enablers kaimahi experienced was collected using a Kaupapa Māori research approach consisting of focus group structures combined with Wānanga as a Kaupapa Māori research methodology. The data was analysed using processes of thematic analysis, where themes were identified and presented in association with the relevant stages of Ngā Kākano.
	The findings of this study saw the organisation stood as a prominent barrier to kaimahi practising Kaupapa Tuku Iho and achieving flourishing. This reflected a need for the organisation to make improvements to support kaimahi in all necessary forms that enable them to achieve flourishing as reflected in positive states of being. It became apparent that most kaimahi were able to achieve flourishing through the practice of Kaupapa Tuku Iho between, amongst and across all kaimahi throughout the organisation irrespective of direct support from the organisation.

text: Proposing a Kaupapa Tuku Iho informed Māori model for practice to enhance cultural competence and foster kaimahi flourishing within health and social service providers Kaupapa Tuku Iho are Māori values that have been used across various social institutions to inform culturally competent practices with those accessing services. This thesis set out to promote the use Kaupapa Tuku Iho to not only enhance cultural competence and culturally appropriate services, but to take a step further and explore factors that foster the flourishing of kaimahi (workers) who deliver those services. There is research that suggests kaimahi in health and social services are overworked, burdened by stressed and approaching a state of compassion fatigue. This is detrimental for those both delivering and accessing services. This study will explore factors that foster kaimahi flourishing and enable kaimahi to practice Kaupapa Tuku Iho, along with factors that stand as barriers to achieving flourishing and culturally competent practice.
Furthermore, I have developed Ngā Kākano, which is a values-based model informed by Kaupapa Tuku Iho that aims to foster kaimahi flourishing and achieve culturally competent practice within health and social service providers. Ngā Kākano has been aligned to various psychological disciplines, including Community Psychology, Industrial-Organisational Psychology and Indigenous Psychology.
Data concerning the exploration of barriers and enablers kaimahi experienced was collected using a Kaupapa Māori research approach consisting of focus group structures combined with Wānanga as a Kaupapa Māori research methodology. The data was analysed using processes of thematic analysis, where themes were identified and presented in association with the relevant stages of Ngā Kākano.
	The findings of this study saw the organisation stood as a prominent barrier to kaimahi practising Kaupapa Tuku Iho and achieving flourishing. This reflected a need for the organisation to make improvements to support kaimahi in all necessary forms that enable them to achieve flourishing as reflected in positive states of being. It became apparent that most kaimahi were able to achieve flourishing through the practice of Kaupapa Tuku Iho between, amongst and across all kaimahi throughout the organisation irrespective of direct support from the organisation.

year: 2022