title: Origin of palaeo proglacial lake sediments in Taylor Valley, Antarctica

authors: Milicich, Sarah

abstract: The origin of carbonates found at three locations in the Taylor Valley and their association with different glacial advances is presented. Samples were collected from three locations through the Taylor Valley, specifically Nussbaum Riegel west of Lake Fryxell, Sollas Bench on the slopes above Lake Bonney, and from Pearse Valley. Carbonates were collected primarily from the surficial glacial sediment, though at one site at Nussbaum Riegel a pit indicated the stratigraphy contained multiple carbonate horizons. The carbonate from Nussbaum Riegel was in situ, while at the other two sites the carbonate was incorporated into moraines. 

The oxygen isotope values indicate that carbonates were deposited in lakes with two different origins. δ¹⁸ values of approximately -28% to -32% for the Nussbaum Riegel carbonate samples indicate "Glacial Lake Nussbaum" likely formed during glacial conditions when grounded ice expanded in McMurdo Sound pushing a lobe of ice up the mouth of the Taylor Valley. δ¹⁸ values of approximately -33 %to 38% for carbonate samples from Pearse Valley and Sollas bench indicate that "Glacial Lake Pearse" and the proglacial lake in which the Sollas Bench carbonates were deposited would have formed during interglacial conditions. It is proposed that an expanded Taylor Glacier was advancing though its own proglaical lakes, reworking carbonate sediment deposited in the lakes. The carbon isotopes reflect the nature of the carbon dioxide cycling within the lakes. Strongly positive δ¹³C values are interpreted as reflecting low temperature equilibrium with atmospheric carbon dioxide or freezing processes causing precipitation. 

The trace element chemistry of the carbonates is inferred to indicate that the origin of their composition is primarily controlled by the composition of the precipitating fluid and the mineralogy of the carbonate. Samples containing higher proportions of aragonite have higher concentrations of the larger ions such as barium and strontium, while those with more calcite in the mineral structure contain more of the smaller ions such as magnesium. 

XRD analyses indicate that the Nussbaum Riegel carbonate samples are a mix of dominantly aragonite with some calcite. SEM images of the carbonate crystals show that they are cementing detrital material. Petrographic analysis of the Nussbaum Riegel carbonates indicate that much of the detrital material is volcanic in nature and was likely sourced from the McMurdo Volcanics. The Sollas Bench and Pearse Valley carbonate samples are predominantly aragonite as shown by XRD analyses. SEM images show the crystals in these samples are a mix of radiating needles and randomly oriented needles, pointing to two different processes during precipitation. SEM images also showed the presence of halite within the carbonate samples. 

The Nussbaum Riegel carbonates are inferred to have been deposited during periods of lake level fluctuation, where draining of ground water towards a lower lake level resulted in evaporation at the lake margins and cementation of the surficial sediment. The Sollas Bench and Pearse Valley carbonates were likely deposited under a regime of water removal, either via evaporation or freezing, making these carbonates a mix of evaporites and "cryorites". Cryorite is a new term, being defined as deposits precipitated as a result of concentration by removal of water due to freezing. In this case they appear to be primarily "cryorites". Halite was identified within many of the carbonate samples and gypsum was found associated with them. This suggests that there was a strongly concentrated brine present at the time of precipitation. 

The source of the salt in the western end in the Taylor Valley is likely to be an evaporate sequence in a subglacial depression indicated on subglacial profiles, currently being overridden by Taylor Glacier. The evaporites could have deposited during a warmer period when the Ferrar Valley was a fjord. Seawater would then have overflowed into Taylor Valley at its convergence with the Ferrar Valley. The resulting lakes then evaporating in the deep depression. Salts are currently being reworked into the valley, a similar situation is proposed for the Sollas Bench carbonates

text: Origin of palaeo proglacial lake sediments in Taylor Valley, Antarctica The origin of carbonates found at three locations in the Taylor Valley and their association with different glacial advances is presented. Samples were collected from three locations through the Taylor Valley, specifically Nussbaum Riegel west of Lake Fryxell, Sollas Bench on the slopes above Lake Bonney, and from Pearse Valley. Carbonates were collected primarily from the surficial glacial sediment, though at one site at Nussbaum Riegel a pit indicated the stratigraphy contained multiple carbonate horizons. The carbonate from Nussbaum Riegel was in situ, while at the other two sites the carbonate was incorporated into moraines. 

The oxygen isotope values indicate that carbonates were deposited in lakes with two different origins. δ¹⁸ values of approximately -28% to -32% for the Nussbaum Riegel carbonate samples indicate "Glacial Lake Nussbaum" likely formed during glacial conditions when grounded ice expanded in McMurdo Sound pushing a lobe of ice up the mouth of the Taylor Valley. δ¹⁸ values of approximately -33 %to 38% for carbonate samples from Pearse Valley and Sollas bench indicate that "Glacial Lake Pearse" and the proglacial lake in which the Sollas Bench carbonates were deposited would have formed during interglacial conditions. It is proposed that an expanded Taylor Glacier was advancing though its own proglaical lakes, reworking carbonate sediment deposited in the lakes. The carbon isotopes reflect the nature of the carbon dioxide cycling within the lakes. Strongly positive δ¹³C values are interpreted as reflecting low temperature equilibrium with atmospheric carbon dioxide or freezing processes causing precipitation. 

The trace element chemistry of the carbonates is inferred to indicate that the origin of their composition is primarily controlled by the composition of the precipitating fluid and the mineralogy of the carbonate. Samples containing higher proportions of aragonite have higher concentrations of the larger ions such as barium and strontium, while those with more calcite in the mineral structure contain more of the smaller ions such as magnesium. 

XRD analyses indicate that the Nussbaum Riegel carbonate samples are a mix of dominantly aragonite with some calcite. SEM images of the carbonate crystals show that they are cementing detrital material. Petrographic analysis of the Nussbaum Riegel carbonates indicate that much of the detrital material is volcanic in nature and was likely sourced from the McMurdo Volcanics. The Sollas Bench and Pearse Valley carbonate samples are predominantly aragonite as shown by XRD analyses. SEM images show the crystals in these samples are a mix of radiating needles and randomly oriented needles, pointing to two different processes during precipitation. SEM images also showed the presence of halite within the carbonate samples. 

The Nussbaum Riegel carbonates are inferred to have been deposited during periods of lake level fluctuation, where draining of ground water towards a lower lake level resulted in evaporation at the lake margins and cementation of the surficial sediment. The Sollas Bench and Pearse Valley carbonates were likely deposited under a regime of water removal, either via evaporation or freezing, making these carbonates a mix of evaporites and "cryorites". Cryorite is a new term, being defined as deposits precipitated as a result of concentration by removal of water due to freezing. In this case they appear to be primarily "cryorites". Halite was identified within many of the carbonate samples and gypsum was found associated with them. This suggests that there was a strongly concentrated brine present at the time of precipitation. 

The source of the salt in the western end in the Taylor Valley is likely to be an evaporate sequence in a subglacial depression indicated on subglacial profiles, currently being overridden by Taylor Glacier. The evaporites could have deposited during a warmer period when the Ferrar Valley was a fjord. Seawater would then have overflowed into Taylor Valley at its convergence with the Ferrar Valley. The resulting lakes then evaporating in the deep depression. Salts are currently being reworked into the valley, a similar situation is proposed for the Sollas Bench carbonates

year: 2005

title: Food webs in the lower Waikato River and the role of hydrogeomorphic complexity

authors: Pingram, Michael Alister

subjects: Waikato River

abstract: Large rivers are fundamental to human societies and consequently their ecosystems have come under increasing pressure from a range of developments and uses. Despite this, there is still a major knowledge gap understanding food webs supporting fisheries of large river ecosystems. Quantifying the contributions of carbon sources that support food webs is an important and growing field of ecological research, with implications for future management and rehabilitation of large rivers. I reviewed theoretical concepts addressing carbon flow in large river food webs where organic matter from floodplains (Flood Pulse Concept), local aquatic sources (Riverine Productivity Model), or leakage from upstream processing of terrestrial organic matter (River Continuum Concept) can fuel secondary production. Recent empirical evidence highlights the importance of autochthonous carbon, especially in the form of benthic algae and phytoplankton, to food webs in a variety of large rivers along with a range of secondary carbon sources that can assume importance depending on temporal and spatial variation in hydrogeomorphic conditions. The geographic spread of studies addressing carbon flow in large river food webs is steadily increasing, although information remains sparse on temperate Southern Hemisphere rivers and long-term data sets on carbon flow are generally lacking. I measured natural abundances of stable carbon (δ13C) and nitrogen (δ15N) isotopes to quantify spatial and temporal patterns of carbon flow through aquatic food webs in the lowland section of New Zealand’s longest river, the Waikato River. Zones of potential ecological importance influencing carbon transfer along the lower Waikato River were identified using a combination of (i) high-frequency, along-river water quality measurements collected during four seasons and (ii) river channel morphology data derived from aerial photos. A multivariate statistical approach was developed to identify three hydrogeomorphic zones shaped by the physical complexity and channel character of constituent river reaches, and characterised by shifts, sometimes transitional, of physico-chemical variables. Changes in water clarity, chlorophyll fluorescence and specific conductance were driven by tributary inflows and tidal influence. 
Carbon flow estimated using the mixing model IsoSource supported predictions of the Riverine Productivity Model, with autochthonous algae and biofilms (phytomicrobenthos) the most important basal carbon sources contributing to consumer biomass in all three zones. These sources were often supported by C3 aquatic macrophytes and allochthonous C3 riparian plants. However, the relative importance of organic carbon sources appeared to change depending on season and zone, likely in response to variations in water temperature and flow, particularly in the unconstrained zone of the lower river. It was also demonstrated that to draw robust conclusions, consideration must be given to quantifying the isotopic signatures of organisms lower in the food web, as these can change significantly between sampling times and hydrogeomorphic zones.
Tributary confluences can be hotspots for biological production and provide novel carbon sources from donor sub-catchments in large river systems. Littoral food webs and water quality were compared between two main stem habitats (constrained and unconstrained hydrogeomorphic zones) and tributary junctions representing those fed by streams, lakes and wetlands during seasonal low flows when these habitats were likely to be most different. δ13C and δ15N isotopes were then employed using the Bayesian statistics R package Stable Isotope Analysis in R (SIAR) to estimate carbon flow through food webs and also to estimate measures of trophic structure. Pathways were also tested using analysis of fish stomach contents. SIAR mixing models confirmed that autochthonous benthic carbon was the most important carbon source to littoral food webs in all habitats. Riparian carbon appeared to be the most important secondary carbon source to fish consumers, and estimates of its contribution were often greater in tributary junctions compared to fish of the same species in the main stem. Trophic patterns of fish species collected in both the main stem and tributary junctions were similar amongst habitats, as were community metrics estimated using stable isotope signatures and SIAR. This study demonstrates that, while they may add to the lateral complexity of the riverscape, permanently connected habitats such as tributary junctions do not necessarily contribute to overall food web complexity. In this study tributary junctions tended to be steep-sided, and complex littoral habitats containing woody debris and macrophytes were typically rare, potentially limiting the development of more complex food webs. 
These results contribute to the ever-improving data regarding food web ecology in large rivers, particularly with regard to carbon flow, and the role played by lateral habitats and hydrogeomorphic zones in shaping these processes. This study also provides information and recommendations that provide direction for future research and management actions aimed at aiding the rehabilitation of the lower Waikato River, its riverscape and biological communities.

text: Food webs in the lower Waikato River and the role of hydrogeomorphic complexity Large rivers are fundamental to human societies and consequently their ecosystems have come under increasing pressure from a range of developments and uses. Despite this, there is still a major knowledge gap understanding food webs supporting fisheries of large river ecosystems. Quantifying the contributions of carbon sources that support food webs is an important and growing field of ecological research, with implications for future management and rehabilitation of large rivers. I reviewed theoretical concepts addressing carbon flow in large river food webs where organic matter from floodplains (Flood Pulse Concept), local aquatic sources (Riverine Productivity Model), or leakage from upstream processing of terrestrial organic matter (River Continuum Concept) can fuel secondary production. Recent empirical evidence highlights the importance of autochthonous carbon, especially in the form of benthic algae and phytoplankton, to food webs in a variety of large rivers along with a range of secondary carbon sources that can assume importance depending on temporal and spatial variation in hydrogeomorphic conditions. The geographic spread of studies addressing carbon flow in large river food webs is steadily increasing, although information remains sparse on temperate Southern Hemisphere rivers and long-term data sets on carbon flow are generally lacking. I measured natural abundances of stable carbon (δ13C) and nitrogen (δ15N) isotopes to quantify spatial and temporal patterns of carbon flow through aquatic food webs in the lowland section of New Zealand’s longest river, the Waikato River. Zones of potential ecological importance influencing carbon transfer along the lower Waikato River were identified using a combination of (i) high-frequency, along-river water quality measurements collected during four seasons and (ii) river channel morphology data derived from aerial photos. A multivariate statistical approach was developed to identify three hydrogeomorphic zones shaped by the physical complexity and channel character of constituent river reaches, and characterised by shifts, sometimes transitional, of physico-chemical variables. Changes in water clarity, chlorophyll fluorescence and specific conductance were driven by tributary inflows and tidal influence. 
Carbon flow estimated using the mixing model IsoSource supported predictions of the Riverine Productivity Model, with autochthonous algae and biofilms (phytomicrobenthos) the most important basal carbon sources contributing to consumer biomass in all three zones. These sources were often supported by C3 aquatic macrophytes and allochthonous C3 riparian plants. However, the relative importance of organic carbon sources appeared to change depending on season and zone, likely in response to variations in water temperature and flow, particularly in the unconstrained zone of the lower river. It was also demonstrated that to draw robust conclusions, consideration must be given to quantifying the isotopic signatures of organisms lower in the food web, as these can change significantly between sampling times and hydrogeomorphic zones.
Tributary confluences can be hotspots for biological production and provide novel carbon sources from donor sub-catchments in large river systems. Littoral food webs and water quality were compared between two main stem habitats (constrained and unconstrained hydrogeomorphic zones) and tributary junctions representing those fed by streams, lakes and wetlands during seasonal low flows when these habitats were likely to be most different. δ13C and δ15N isotopes were then employed using the Bayesian statistics R package Stable Isotope Analysis in R (SIAR) to estimate carbon flow through food webs and also to estimate measures of trophic structure. Pathways were also tested using analysis of fish stomach contents. SIAR mixing models confirmed that autochthonous benthic carbon was the most important carbon source to littoral food webs in all habitats. Riparian carbon appeared to be the most important secondary carbon source to fish consumers, and estimates of its contribution were often greater in tributary junctions compared to fish of the same species in the main stem. Trophic patterns of fish species collected in both the main stem and tributary junctions were similar amongst habitats, as were community metrics estimated using stable isotope signatures and SIAR. This study demonstrates that, while they may add to the lateral complexity of the riverscape, permanently connected habitats such as tributary junctions do not necessarily contribute to overall food web complexity. In this study tributary junctions tended to be steep-sided, and complex littoral habitats containing woody debris and macrophytes were typically rare, potentially limiting the development of more complex food webs. 
These results contribute to the ever-improving data regarding food web ecology in large rivers, particularly with regard to carbon flow, and the role played by lateral habitats and hydrogeomorphic zones in shaping these processes. This study also provides information and recommendations that provide direction for future research and management actions aimed at aiding the rehabilitation of the lower Waikato River, its riverscape and biological communities.

year: 2014

title: Māori and Dementia: Māori health professionals’ perceptions of dementia, support offered and suggested improvements

authors: Townsend, Marie

subjects: dementia

abstract: E iti noa ana, nā te aroha (It is the giving that counts and not the size of the gift) The purpose of this thesis was to investigate the perceptions of Māori health professionals about Māori elders and dementia. The study aimed to describe: Māori health care providers’ understandings of dementia; traditional versus contemporary understandings; how cultural beliefs affect experience; how Māori cope with dementia; key issues relevant to Māori people with dementia; and how services can be improved to meet the needs of aged Māori. The usefulness and possible cultural adaptation of the biomedical model has been explored within the context of a Māori worldview and the perceptions of participants. Semi-structured and in-depth interviews were conducted with eight mental health professionals and one caregiver. The information gathered at interviews was recorded within verbatim transcripts, which were written and returned to the participants for feedback. A qualitative data analysis was carried out on the approved transcripts. The main findings suggest that Māori health professionals recognise that many Māori perceive dementia both from a traditional cultural perspective, associated with spirituality as well as a holistic understanding of wellness. Key issues identified by participants were: that there is fear associated with mental health facilities; the exclusion of cultural values and understandings from service providers is detrimental to the wellbeing of Māori elders; Māori do not understand the symptoms typically associated with dementia as an illness; there is a need for information and education within an appropriate frame for whānau; disjointed and multiple service providers inhibits Māori from accessing facilities offered; and that there is a real need for further services. It was considered important that mental health services are culturally appropriate, show respect for Māori values; are coordinated and sensitive; encourage and continue the development of a Māori mental health workforce; and further develop kaupapa Māori services for Māori elders. The main implication of this research is that further investigation into Māori and dementia is required. Recommendations are made with a view towards better addressing some of the mental health needs of Māori elders.

text: Māori and Dementia: Māori health professionals’ perceptions of dementia, support offered and suggested improvements E iti noa ana, nā te aroha (It is the giving that counts and not the size of the gift) The purpose of this thesis was to investigate the perceptions of Māori health professionals about Māori elders and dementia. The study aimed to describe: Māori health care providers’ understandings of dementia; traditional versus contemporary understandings; how cultural beliefs affect experience; how Māori cope with dementia; key issues relevant to Māori people with dementia; and how services can be improved to meet the needs of aged Māori. The usefulness and possible cultural adaptation of the biomedical model has been explored within the context of a Māori worldview and the perceptions of participants. Semi-structured and in-depth interviews were conducted with eight mental health professionals and one caregiver. The information gathered at interviews was recorded within verbatim transcripts, which were written and returned to the participants for feedback. A qualitative data analysis was carried out on the approved transcripts. The main findings suggest that Māori health professionals recognise that many Māori perceive dementia both from a traditional cultural perspective, associated with spirituality as well as a holistic understanding of wellness. Key issues identified by participants were: that there is fear associated with mental health facilities; the exclusion of cultural values and understandings from service providers is detrimental to the wellbeing of Māori elders; Māori do not understand the symptoms typically associated with dementia as an illness; there is a need for information and education within an appropriate frame for whānau; disjointed and multiple service providers inhibits Māori from accessing facilities offered; and that there is a real need for further services. It was considered important that mental health services are culturally appropriate, show respect for Māori values; are coordinated and sensitive; encourage and continue the development of a Māori mental health workforce; and further develop kaupapa Māori services for Māori elders. The main implication of this research is that further investigation into Māori and dementia is required. Recommendations are made with a view towards better addressing some of the mental health needs of Māori elders.

year: 2011