title: Magnitude and controls on the net carbon balance of a New Zealand raised bog

authors: Goodrich, Jordan Paul

subjects: peatland

abstract: Peatlands play an important role in the Earth system as both persistent carbon dioxide (CO₂) sinks and methane (CH₄) sources. However, large uncertainties remain in our understanding of peatland carbon cycle – climate feedbacks. The majority of research has been conducted in the Northern Hemisphere as most of the global peatland area is located there. Few data have been collected in Southern Hemisphere peatlands and there is a limited basis for predicting how these systems will respond to changing climatic drivers and other anthropogenic forcings such as drainage for agriculture. Furthermore, it is unclear whether our knowledge of peatland functioning and carbon (C) cycling from the Northern Hemisphere translates to systems that have developed under different climatic and hydrologic settings with unique vegetation.  

To gain a better understanding of peatland carbon and greenhouse gas exchange in a globally distinct and unique peatland type, I used eddy covariance to measure net ecosystem CO₂ exchange (NEE) and CH₄ flux (FCH₄)  in an undisturbed New Zealand raised bog over ~2.5 years. The overarching goals of this research were to determine magnitudes of the main components of the ecosystem C budget, gross primary production (GPP), ecosystem respiration (ER), and FCH₄, and their sensitivity to environmental and physical drivers. 

With respect to CO₂ exchange, high VPD periods restricted the light-saturated photosynthetic capacity during clear sky days. Elevated VPD was also the only condition that led to reductions in daily total GPP, a response likely triggered to reduce transpiration water losses. These results have important implications for the future C sink strength of New Zealand peatlands given a trend toward drier summers with clearer skies and higher VPD.

With respect to FCH₄, a severe drought during summer 2013 allowed me to explore the interacting controls of temperature and water table depth. During 2012, a relatively average meteorological year, annual total FCH₄ was 21.5 g CH₄⁻ C m⁻² yr⁻1, whereas total FCH₄ during the drought year (2013) was 14.5 g CH₄⁻C m⁻² yr⁻¹. I found that water table depth was the most important overarching control on FCH₄ over various timescales from weekly to inter-annual. Water table depth regulated the temperature sensitivity of FCH₄, which was highest when the water table was within 50 – 80 mm of the surface. This depth range corresponds to the relatively shallow rooting zone of the dominant vegetation, which may provide much of the substrate for methane production.

Kopuatai bog was a very strong C sink compared to Northern Hemisphere bogs and fens. Despite the elevated ER during the drought year, Kopuatai was a sink of 74.5 gC m⁻², which is at the high end of published Northern Hemisphere estimates. The more average meteorological year (2012) resulted in a much larger sink of 152 gC m⁻². This work has revealed the importance of atmospheric controls on plant CO₂ uptake and hydrologic (i.e. water table) effects on ecosystem respiration and FCH₄, when considering the overall C balance. These effects imply that the future C sink capacity of Kopuatai bog may be reduced due to the long-term trend toward drier, sunnier summers and more frequent droughts in the region.

text: Magnitude and controls on the net carbon balance of a New Zealand raised bog Peatlands play an important role in the Earth system as both persistent carbon dioxide (CO₂) sinks and methane (CH₄) sources. However, large uncertainties remain in our understanding of peatland carbon cycle – climate feedbacks. The majority of research has been conducted in the Northern Hemisphere as most of the global peatland area is located there. Few data have been collected in Southern Hemisphere peatlands and there is a limited basis for predicting how these systems will respond to changing climatic drivers and other anthropogenic forcings such as drainage for agriculture. Furthermore, it is unclear whether our knowledge of peatland functioning and carbon (C) cycling from the Northern Hemisphere translates to systems that have developed under different climatic and hydrologic settings with unique vegetation.  

To gain a better understanding of peatland carbon and greenhouse gas exchange in a globally distinct and unique peatland type, I used eddy covariance to measure net ecosystem CO₂ exchange (NEE) and CH₄ flux (FCH₄)  in an undisturbed New Zealand raised bog over ~2.5 years. The overarching goals of this research were to determine magnitudes of the main components of the ecosystem C budget, gross primary production (GPP), ecosystem respiration (ER), and FCH₄, and their sensitivity to environmental and physical drivers. 

With respect to CO₂ exchange, high VPD periods restricted the light-saturated photosynthetic capacity during clear sky days. Elevated VPD was also the only condition that led to reductions in daily total GPP, a response likely triggered to reduce transpiration water losses. These results have important implications for the future C sink strength of New Zealand peatlands given a trend toward drier summers with clearer skies and higher VPD.

With respect to FCH₄, a severe drought during summer 2013 allowed me to explore the interacting controls of temperature and water table depth. During 2012, a relatively average meteorological year, annual total FCH₄ was 21.5 g CH₄⁻ C m⁻² yr⁻1, whereas total FCH₄ during the drought year (2013) was 14.5 g CH₄⁻C m⁻² yr⁻¹. I found that water table depth was the most important overarching control on FCH₄ over various timescales from weekly to inter-annual. Water table depth regulated the temperature sensitivity of FCH₄, which was highest when the water table was within 50 – 80 mm of the surface. This depth range corresponds to the relatively shallow rooting zone of the dominant vegetation, which may provide much of the substrate for methane production.

Kopuatai bog was a very strong C sink compared to Northern Hemisphere bogs and fens. Despite the elevated ER during the drought year, Kopuatai was a sink of 74.5 gC m⁻², which is at the high end of published Northern Hemisphere estimates. The more average meteorological year (2012) resulted in a much larger sink of 152 gC m⁻². This work has revealed the importance of atmospheric controls on plant CO₂ uptake and hydrologic (i.e. water table) effects on ecosystem respiration and FCH₄, when considering the overall C balance. These effects imply that the future C sink capacity of Kopuatai bog may be reduced due to the long-term trend toward drier, sunnier summers and more frequent droughts in the region.

year: 2015

title: Capital formation and agricultural growth in China

authors: Ma, Hengyun

subjects: Lewis-Model

abstract: The paper considers the role and determinants of capital formation in Chinese agriculture and, in particular, the effects of capital formation on agricultural total factor productivity (TFP) growth. The results show that capital investment in agriculture by both government and farmers has risen significantly in the past two and a half decades, particularly in recent years. As China remains in the early stages of agricultural policy transition, its political economy would suggest that there will likely be more public investment in, and more subsidies to, agriculture in the coming years. Increased public investment in agriculture appears to have also induced increased farmers' capital formation in agriculture. Credit policy, the overall growth of farmer's income, rural wages, and comparative advantage of commodities are important factors that may facilitate farmers' investment in agriculture. The results also show that the successful growth of China's agriculture has been associated with its high TFP growth. Both public and private agricultural capital formations have played an important role in raising China's agricultural productivity. The TFP decomposition analyses show that technological change is a primary driver of the TFP growth in China's agriculture.

text: Capital formation and agricultural growth in China The paper considers the role and determinants of capital formation in Chinese agriculture and, in particular, the effects of capital formation on agricultural total factor productivity (TFP) growth. The results show that capital investment in agriculture by both government and farmers has risen significantly in the past two and a half decades, particularly in recent years. As China remains in the early stages of agricultural policy transition, its political economy would suggest that there will likely be more public investment in, and more subsidies to, agriculture in the coming years. Increased public investment in agriculture appears to have also induced increased farmers' capital formation in agriculture. Credit policy, the overall growth of farmer's income, rural wages, and comparative advantage of commodities are important factors that may facilitate farmers' investment in agriculture. The results also show that the successful growth of China's agriculture has been associated with its high TFP growth. Both public and private agricultural capital formations have played an important role in raising China's agricultural productivity. The TFP decomposition analyses show that technological change is a primary driver of the TFP growth in China's agriculture.

year: 2013

title: Māori transitions into tertiary education

authors: Amundsen, Diana Leigh

subjects: Maori

abstract: This thesis critically examines Māori transitions into tertiary education. The research explored the lived transition experiences of 20 Māori tertiary education students in the Bay of Plenty region. Historical and contemporary factors in Aotearoa influencing effective Māori student transitions into tertiary education were investigated. Data were collected and analysed through repeated semistructured interviews and focus groups over the 2016-2018 period with 20 Māori students enrolled in a wānanga, a polytechnic and a university. Participants experienced their transition as a journey, continuously evolving their identities and agency in relation to the tertiary education environments and social structures they encountered.
The findings suggest that transitions to tertiary education for Māori students involve a reciprocal interplay of identity, agency and structure which support or constrain transition experiences. Effective transition experiences were underpinned by processes of continuity enabling identity growth. Support was central to how well participants perceived their transition—racism and lack of support were significant barriers; suitable support was a significant enabler.
An over-riding theme from this research related to the interplay of power relations and Māori identity. How effectively participants developed a sense of belonging (or alienation) and identity growth linked to the tertiary education environments they encountered during their transition. Within wānanga, participants felt their Māori cultural identity was highly valued; within polytechnics, there was a sense that Māori culture is included but more could be done; within universities, a need for more inclusive practices to support Māori learner requirements was identified.
Lastly, this research was conducted by a Pākehā researcher working across kaupapa Māori spaces within interpretive and critical paradigms. Unexpected moments of struggle, discomfort and vulnerability opened up new and deeper understanding of implications for Pākehā educators and researchers engaging across Māori research spaces. This thesis argues for Pākehā to use their privilege to foster more equitable social structures. Equitable social structures would be beneficial for Māori transitions into tertiary education environments.

text: Māori transitions into tertiary education This thesis critically examines Māori transitions into tertiary education. The research explored the lived transition experiences of 20 Māori tertiary education students in the Bay of Plenty region. Historical and contemporary factors in Aotearoa influencing effective Māori student transitions into tertiary education were investigated. Data were collected and analysed through repeated semistructured interviews and focus groups over the 2016-2018 period with 20 Māori students enrolled in a wānanga, a polytechnic and a university. Participants experienced their transition as a journey, continuously evolving their identities and agency in relation to the tertiary education environments and social structures they encountered.
The findings suggest that transitions to tertiary education for Māori students involve a reciprocal interplay of identity, agency and structure which support or constrain transition experiences. Effective transition experiences were underpinned by processes of continuity enabling identity growth. Support was central to how well participants perceived their transition—racism and lack of support were significant barriers; suitable support was a significant enabler.
An over-riding theme from this research related to the interplay of power relations and Māori identity. How effectively participants developed a sense of belonging (or alienation) and identity growth linked to the tertiary education environments they encountered during their transition. Within wānanga, participants felt their Māori cultural identity was highly valued; within polytechnics, there was a sense that Māori culture is included but more could be done; within universities, a need for more inclusive practices to support Māori learner requirements was identified.
Lastly, this research was conducted by a Pākehā researcher working across kaupapa Māori spaces within interpretive and critical paradigms. Unexpected moments of struggle, discomfort and vulnerability opened up new and deeper understanding of implications for Pākehā educators and researchers engaging across Māori research spaces. This thesis argues for Pākehā to use their privilege to foster more equitable social structures. Equitable social structures would be beneficial for Māori transitions into tertiary education environments.

year: 2019