title: Assessing dissolved organic carbon export from Kopuatai bog, New Zealand

authors: Sturgeon, Catherine

subjects: peatland

abstract: Peatlands sequester carbon (C) through CO₂ uptake and, ultimately, storage as peat. Carbon is lost from peatlands though gaseous pathways (as CO₂ and CH₄) and water pathways as dissolved organic C (DOC), dissolved inorganic C (DIC), particulate organic C (POC) or dissolved CO₂ and CH₄. Many studies have shown that the loss of C through DOC export is an important component of the annual C budget, but there are very few published studies where atmospheric fluxes of CO₂ and CH₄ and waterborne fluxes of DOC are measured at the same time. Also, little is known about the spatial variations in DOC concentration within peatlands and the processes leading to the delivery of DOC into rivers.
The research described in this thesis focuses on understanding the ways in which vegetation, temperature, peat quality and hydrology interact to determine variability in DOC concentrations and export, both seasonally and spatially, at Kopuatai bog. DOC concentrations were measured at 14 sites across the bog for a year. At each site peat pore water was sampled from three different depths and represented three different vegetation types dominated by Empodisma robustum (jointed wire rush), Leptospermum scoparium (manuka) and Sporadanthus ferrugineus. There were no strong seasonal trends in DOC concentration, possibly due to the small seasonal range in temperatures. DOC concentrations varied spatially, with highest concentrations found under L. scoparium vegetation, likely due to differing chemical properties of plant materials leading to higher decomposition rates. DOC concentration did not vary significantly with depth.
DOC export was estimated using a water balance based approach where evaporation (E), precipitation (P) and change in storage were measured to determine water discharge (Q) from the eddy covariance (EC) footprint. Discharge was then multiplied by average DOC concentrations within the EC footprint to derive DOC export. This method had not been directly applied in the literature. It was estimated that 11.7 ± 0.82 g C m⁻² of DOC was exported from the EC footprint from the year 1 February 2012 to 1 February 2013, which is at the lower end of the range when compared to literature values. DOC export had strong seasonal variation with highest export during the winter due to high rainfall and lowest in summer due to low rainfall. A simple method to estimate DOC export was proposed using the strong correlations between DOC export and monthly P and P–E.
When annual DOC export was compared to annual net ecosystem exchange (NEE) at Kopuatai, DOC export was equivalent to only 6% of CO₂ sequestered in a year. This is in contrast to the literature where, on average, DOC export is often equal to around 25% of NEE. Preliminary analyses shows that NEE values are significantly higher at Kopuatai than NEE published for Northern Hemisphere peatlands and this is likely an effect of the dominance by vascular plants and the year-round growing conditions at Kopuatai.

text: Assessing dissolved organic carbon export from Kopuatai bog, New Zealand Peatlands sequester carbon (C) through CO₂ uptake and, ultimately, storage as peat. Carbon is lost from peatlands though gaseous pathways (as CO₂ and CH₄) and water pathways as dissolved organic C (DOC), dissolved inorganic C (DIC), particulate organic C (POC) or dissolved CO₂ and CH₄. Many studies have shown that the loss of C through DOC export is an important component of the annual C budget, but there are very few published studies where atmospheric fluxes of CO₂ and CH₄ and waterborne fluxes of DOC are measured at the same time. Also, little is known about the spatial variations in DOC concentration within peatlands and the processes leading to the delivery of DOC into rivers.
The research described in this thesis focuses on understanding the ways in which vegetation, temperature, peat quality and hydrology interact to determine variability in DOC concentrations and export, both seasonally and spatially, at Kopuatai bog. DOC concentrations were measured at 14 sites across the bog for a year. At each site peat pore water was sampled from three different depths and represented three different vegetation types dominated by Empodisma robustum (jointed wire rush), Leptospermum scoparium (manuka) and Sporadanthus ferrugineus. There were no strong seasonal trends in DOC concentration, possibly due to the small seasonal range in temperatures. DOC concentrations varied spatially, with highest concentrations found under L. scoparium vegetation, likely due to differing chemical properties of plant materials leading to higher decomposition rates. DOC concentration did not vary significantly with depth.
DOC export was estimated using a water balance based approach where evaporation (E), precipitation (P) and change in storage were measured to determine water discharge (Q) from the eddy covariance (EC) footprint. Discharge was then multiplied by average DOC concentrations within the EC footprint to derive DOC export. This method had not been directly applied in the literature. It was estimated that 11.7 ± 0.82 g C m⁻² of DOC was exported from the EC footprint from the year 1 February 2012 to 1 February 2013, which is at the lower end of the range when compared to literature values. DOC export had strong seasonal variation with highest export during the winter due to high rainfall and lowest in summer due to low rainfall. A simple method to estimate DOC export was proposed using the strong correlations between DOC export and monthly P and P–E.
When annual DOC export was compared to annual net ecosystem exchange (NEE) at Kopuatai, DOC export was equivalent to only 6% of CO₂ sequestered in a year. This is in contrast to the literature where, on average, DOC export is often equal to around 25% of NEE. Preliminary analyses shows that NEE values are significantly higher at Kopuatai than NEE published for Northern Hemisphere peatlands and this is likely an effect of the dominance by vascular plants and the year-round growing conditions at Kopuatai.

year: 2013

title: "Guano and the Opening of the Pacific World: a Global Ecological History” by G.T. Cushman (Cambridge University Press, 2013) [Book Review]

authors: Lowe, David J.

abstract: This article reviews the book: "Guano and the Opening of the Pacific World: a Global Ecological History” by G.T. Cushman.

text: "Guano and the Opening of the Pacific World: a Global Ecological History” by G.T. Cushman (Cambridge University Press, 2013) [Book Review] This article reviews the book: "Guano and the Opening of the Pacific World: a Global Ecological History” by G.T. Cushman.

year: 2017-12-31

title: Me ko Māui: Harnessing the sun to provide better outcomes for marae and communities

authors: Greensill, Waikauri

abstract: Marae are the cultural centres of Māori communities, providing a space for important gatherings both joyful and sad. With the advent of solar energy capture technologies and rising electricity bills, many marae are becoming interested in whether a solar powered system will be beneficial for them. However, marae have unique electricity demand profiles, distinct from commonly modelled building types such as residential or commercial buildings. It is thus difficult to estimate an appropriate solar and battery system size based on annual or even monthly electricity usage data, which may be the only data readily available, requiring more in-depth analysis at a highly site-specific level to find an answer. This thesis aims to increase understanding around how solar power could benefit marae, first by investigating the characteristic electricity demand profile of marae, then by observing how proposed system configurations meet the demand. The potential community benefits arising from such a system was also investigated. Using a year’s worth of half-hourly data from three marae, five characteristic day types were found in the analysis of the demand profile, namely a “Non-Event” profile that maintained a low baseload and accounted for 70% of the days in a year, a “1-Day Event” profile that lasted only a few hours, and for events spanning multiple days a “Start”, “Middle” and “End” day profile that varied greatly in demand magnitude. The demand profiles were then used to develop an annual demand profile for an average marae that was broadly representative of a wide range of marae. Different configurations of solar and battery powered systems were then applied to the annual demand and a technoeconomic analysis performed to determine whether a specific configuration met the needs of the average marae or not, which then produced a range of acceptable system sizes based on the needs specified. Not many solar and battery configurations resulted in positive economic returns for the marae alone, but widening the scope of the analysis to the surrounding community allows other interests such as local grid resilience to be considered, some of which may justify a marae’s decision to invest in a non-economic system to gain better community benefits. While investigating the use of peer-to-peer energy trading and community energy scenarios, sharing excess energy generated by a system with the wider community was also found to improve the economic outlook of solar for marae.

text: Me ko Māui: Harnessing the sun to provide better outcomes for marae and communities Marae are the cultural centres of Māori communities, providing a space for important gatherings both joyful and sad. With the advent of solar energy capture technologies and rising electricity bills, many marae are becoming interested in whether a solar powered system will be beneficial for them. However, marae have unique electricity demand profiles, distinct from commonly modelled building types such as residential or commercial buildings. It is thus difficult to estimate an appropriate solar and battery system size based on annual or even monthly electricity usage data, which may be the only data readily available, requiring more in-depth analysis at a highly site-specific level to find an answer. This thesis aims to increase understanding around how solar power could benefit marae, first by investigating the characteristic electricity demand profile of marae, then by observing how proposed system configurations meet the demand. The potential community benefits arising from such a system was also investigated. Using a year’s worth of half-hourly data from three marae, five characteristic day types were found in the analysis of the demand profile, namely a “Non-Event” profile that maintained a low baseload and accounted for 70% of the days in a year, a “1-Day Event” profile that lasted only a few hours, and for events spanning multiple days a “Start”, “Middle” and “End” day profile that varied greatly in demand magnitude. The demand profiles were then used to develop an annual demand profile for an average marae that was broadly representative of a wide range of marae. Different configurations of solar and battery powered systems were then applied to the annual demand and a technoeconomic analysis performed to determine whether a specific configuration met the needs of the average marae or not, which then produced a range of acceptable system sizes based on the needs specified. Not many solar and battery configurations resulted in positive economic returns for the marae alone, but widening the scope of the analysis to the surrounding community allows other interests such as local grid resilience to be considered, some of which may justify a marae’s decision to invest in a non-economic system to gain better community benefits. While investigating the use of peer-to-peer energy trading and community energy scenarios, sharing excess energy generated by a system with the wider community was also found to improve the economic outlook of solar for marae.

year: 2024