title: Turbulence transport throughout the heliosphere

authors: Breech, Ben

subjects: mathematics

abstract: We employ a turbulence transport model to compute distributions of turbulence throughout the heliosphere. The model determines the radial dependence of three (coupled) quantities that characterize interplanetary turbulence, the energy per unit mass, the cross helicity or Alfvénicity, and a similarity length scale. A fourth integrated quantity, the plasma temperature, is modified by heat deposition due to turbulent dissipation. The model includes advection, expansion, and reflection effects as well as the tendency toward dynamic alignment, and a von Kármán type dissipation function that represents decay of turbulence due to cascade to small scales. Two types of forcing are also featured, one a simple model of stream shear, and the other a driving in the outer heliosphere associated with wave energy injection due to pickup protons of interstellar origin. Parameters for the model have been tuned using observation data from Voyager and Ulysses. We analyze the constraining observations to provide boundary conditions and parameters that vary with heliocentric latitude, with some extrapolations. The fully assembled model permits the computation of the distribution of turbulence throughout the entire heliosphere, and we present solutions for several appropriate parameter sets.

text: Turbulence transport throughout the heliosphere We employ a turbulence transport model to compute distributions of turbulence throughout the heliosphere. The model determines the radial dependence of three (coupled) quantities that characterize interplanetary turbulence, the energy per unit mass, the cross helicity or Alfvénicity, and a similarity length scale. A fourth integrated quantity, the plasma temperature, is modified by heat deposition due to turbulent dissipation. The model includes advection, expansion, and reflection effects as well as the tendency toward dynamic alignment, and a von Kármán type dissipation function that represents decay of turbulence due to cascade to small scales. Two types of forcing are also featured, one a simple model of stream shear, and the other a driving in the outer heliosphere associated with wave energy injection due to pickup protons of interstellar origin. Parameters for the model have been tuned using observation data from Voyager and Ulysses. We analyze the constraining observations to provide boundary conditions and parameters that vary with heliocentric latitude, with some extrapolations. The fully assembled model permits the computation of the distribution of turbulence throughout the entire heliosphere, and we present solutions for several appropriate parameter sets.

year: 2007

title: Bloom formation, species succession, toxin variability and benthic  recruitment of cyanobacteria in Lake Rotorua, Kaikoura

authors: Ferreira Borges, Hugo Leandro

subjects: cyanobacteria

abstract: Cyanobacteria are an ancient group of photosynthetic prokaryotes that are found in a wide range of habitats including freshwater lakes and rivers. In aquatic ecosystems, under favourable environmental conditions, cyanobacteria can form dense and expansive blooms. The increasing prevalence of cyanobacterial blooms globally has been linked to environmental changes in freshwater ecosystems including anthropogenic eutrophication, catchment modification and climate change. One of the most common genera of bloom-forming cyanobacteria is Microcystis. It can produce microcystins, a potent cyanotoxin that poses a risk to human and animal health. It also possesses physiological adaptations that confer a competitive advantage over other phytoplankton and cyanobacteria. One of these is the ability to vegetatively ‘overwinter’ on sediment surfaces.  When conditions are favourable in spring or summer cells are recruited back into the water column and may provide a substantial inoculum for summer blooms. 
To better understand the variables that promote Microcystis aeruginosa blooms, this study investigated; (i) how environmental variables influence M. aeruginosa bloom formation and species succession during a bloom, as well as the seasonal variability of microcystin production, and (ii) how environmental, biotic and ultrastructural changes in the cells influence recruitment of  benthic M. aeruginosa. The study focused on Lake Rotorua, a small eutrophic lake in Kaikoura, South Island, New Zealand. 
To address the first objective, surface water samples were collected weekly or fortnightly from Lake Rotorua between 14 January 2014 and 27 May 2015. Samples were analysed for cyanobacterial cell density and species composition, total and dissolved nutrients, mcyE genotype composition, and microcystin quota. Temperature was measured using loggers at different depths in the water column and weather data were acquired from the Kaikoura weather station (approximately 8 km from the study site). To address the second objective, surface sediment samples were collected from near-edge (containing Microcystis and Aphanizomenon gracile) and mid-lake (containing predominantly Microcystis) sites in Lake Rotorua. A series of laboratory experiments were undertaken which investigated the effect of ammonium (0, 0.1, 0.2, 0.5, 1 and 5 mg N L-1), light intensity (dark, 1.5, 10, 50 and 100 µmol photon m-2 s-1) and temperature (4, 13, 16, 19 and 25°C) Changes in cellular structures of Microcystis isolated from sediment collected in spring, early and late summer were also analysed using transmission electron microscopy to assess how this influenced recruitment
Cyanobacteria species composition in Lake Rotorua was dominated by Microcystis aeruginosa, Aphanizomenon gracile, and Dolichospermum crassum. Moderate levels of nitrate in the lake appeared to be related to intermittent high-rainfall events during the austral summer of 2014, and may have contributed towards dominance by A. gracile and D. crassum. While both species are capable of nitrogen-fixation, heterocytes were absent. M. aeruginosa blooms subsequently occurred when ammonium concentrations increased, water temperature was high (>27°C), and the total nitrogen: total phosphorus ratio was low. A storm towards the end of the 2014 summer rapidly cooled and mixed the lake, and was followed by bloom collapse. In contrast, an extended drought over summer 2015 resulted in prolonged stratification, increased dissolved reactive phosphorus and very low dissolved inorganic nitrogen concentrations. Cyanobacterial pattern of species succession differed substantially between 2014 and 2015. Aphanizomenon gracile and D. crassum contained a higher heterocytes frequency compared to 2014 and M. aeruginosa density remained relatively low. Picocyanobacteria consisting of Aphanocapsa sp. were abundant. There was no relationship between toxic genotype abundance and M. aeruginosa biovolume or environmental parameters. However, univariate analysis showed that there was a significant positive relationship (p<0.001) between microcystin quotas and surface water temperature. 
In all benthic recruitment experiments single cells, rather than colonies, accounted for the majority (>55%) of recruited cells and it was speculated this may have been because they had more immediate access to light and nutrients. Linear Mixed Effect Models (LMEMs) analysis showed that M. aeruginosa recruitment was significantly lower (ANOVA; p<0.001) in near-shore sediment samples, suggesting that A. gracile may elicit allopathic effects on M. aeruginosa. In mid-lake sediment samples, M. aeruginosa recruitment was significantly higher at moderate ammonium concentrations (0.1, 0.2 and 0.5 mg N L-1; ANOVA; p<0.001), at two temperatures (16 and 25°C; ANOVA; p<0.001) and high light intensities (50 and 100 µmol m-2 s-1; ANOVA; p<0.01). Under transmission electron microscopy the area of benthic cells occupied by gas vesicles increased significantly (ANOVA; p<0.001) for the three samples collected during the study period. 
The results highlight the complex successional interplay of cyanobacteria species and their physiological adaptations (e.g., nitrogen fixation, buoyancy regulation). Climate, through its effect on runoff, water temperature and stratification, can lead to successional sequences amongst different cyanobacteria species according to whether the combination of physiological adaptations is advantageous or disadvantageous with environmental change. The benthic recruitment experiments collectively demonstrated that allopathic interactions, ammonium, light and temperature individually and synergistically regulate gas vesicle synthesis and M. aeruginosa recruitment in Lake Rotorua.

text: Bloom formation, species succession, toxin variability and benthic  recruitment of cyanobacteria in Lake Rotorua, Kaikoura Cyanobacteria are an ancient group of photosynthetic prokaryotes that are found in a wide range of habitats including freshwater lakes and rivers. In aquatic ecosystems, under favourable environmental conditions, cyanobacteria can form dense and expansive blooms. The increasing prevalence of cyanobacterial blooms globally has been linked to environmental changes in freshwater ecosystems including anthropogenic eutrophication, catchment modification and climate change. One of the most common genera of bloom-forming cyanobacteria is Microcystis. It can produce microcystins, a potent cyanotoxin that poses a risk to human and animal health. It also possesses physiological adaptations that confer a competitive advantage over other phytoplankton and cyanobacteria. One of these is the ability to vegetatively ‘overwinter’ on sediment surfaces.  When conditions are favourable in spring or summer cells are recruited back into the water column and may provide a substantial inoculum for summer blooms. 
To better understand the variables that promote Microcystis aeruginosa blooms, this study investigated; (i) how environmental variables influence M. aeruginosa bloom formation and species succession during a bloom, as well as the seasonal variability of microcystin production, and (ii) how environmental, biotic and ultrastructural changes in the cells influence recruitment of  benthic M. aeruginosa. The study focused on Lake Rotorua, a small eutrophic lake in Kaikoura, South Island, New Zealand. 
To address the first objective, surface water samples were collected weekly or fortnightly from Lake Rotorua between 14 January 2014 and 27 May 2015. Samples were analysed for cyanobacterial cell density and species composition, total and dissolved nutrients, mcyE genotype composition, and microcystin quota. Temperature was measured using loggers at different depths in the water column and weather data were acquired from the Kaikoura weather station (approximately 8 km from the study site). To address the second objective, surface sediment samples were collected from near-edge (containing Microcystis and Aphanizomenon gracile) and mid-lake (containing predominantly Microcystis) sites in Lake Rotorua. A series of laboratory experiments were undertaken which investigated the effect of ammonium (0, 0.1, 0.2, 0.5, 1 and 5 mg N L-1), light intensity (dark, 1.5, 10, 50 and 100 µmol photon m-2 s-1) and temperature (4, 13, 16, 19 and 25°C) Changes in cellular structures of Microcystis isolated from sediment collected in spring, early and late summer were also analysed using transmission electron microscopy to assess how this influenced recruitment
Cyanobacteria species composition in Lake Rotorua was dominated by Microcystis aeruginosa, Aphanizomenon gracile, and Dolichospermum crassum. Moderate levels of nitrate in the lake appeared to be related to intermittent high-rainfall events during the austral summer of 2014, and may have contributed towards dominance by A. gracile and D. crassum. While both species are capable of nitrogen-fixation, heterocytes were absent. M. aeruginosa blooms subsequently occurred when ammonium concentrations increased, water temperature was high (>27°C), and the total nitrogen: total phosphorus ratio was low. A storm towards the end of the 2014 summer rapidly cooled and mixed the lake, and was followed by bloom collapse. In contrast, an extended drought over summer 2015 resulted in prolonged stratification, increased dissolved reactive phosphorus and very low dissolved inorganic nitrogen concentrations. Cyanobacterial pattern of species succession differed substantially between 2014 and 2015. Aphanizomenon gracile and D. crassum contained a higher heterocytes frequency compared to 2014 and M. aeruginosa density remained relatively low. Picocyanobacteria consisting of Aphanocapsa sp. were abundant. There was no relationship between toxic genotype abundance and M. aeruginosa biovolume or environmental parameters. However, univariate analysis showed that there was a significant positive relationship (p<0.001) between microcystin quotas and surface water temperature. 
In all benthic recruitment experiments single cells, rather than colonies, accounted for the majority (>55%) of recruited cells and it was speculated this may have been because they had more immediate access to light and nutrients. Linear Mixed Effect Models (LMEMs) analysis showed that M. aeruginosa recruitment was significantly lower (ANOVA; p<0.001) in near-shore sediment samples, suggesting that A. gracile may elicit allopathic effects on M. aeruginosa. In mid-lake sediment samples, M. aeruginosa recruitment was significantly higher at moderate ammonium concentrations (0.1, 0.2 and 0.5 mg N L-1; ANOVA; p<0.001), at two temperatures (16 and 25°C; ANOVA; p<0.001) and high light intensities (50 and 100 µmol m-2 s-1; ANOVA; p<0.01). Under transmission electron microscopy the area of benthic cells occupied by gas vesicles increased significantly (ANOVA; p<0.001) for the three samples collected during the study period. 
The results highlight the complex successional interplay of cyanobacteria species and their physiological adaptations (e.g., nitrogen fixation, buoyancy regulation). Climate, through its effect on runoff, water temperature and stratification, can lead to successional sequences amongst different cyanobacteria species according to whether the combination of physiological adaptations is advantageous or disadvantageous with environmental change. The benthic recruitment experiments collectively demonstrated that allopathic interactions, ammonium, light and temperature individually and synergistically regulate gas vesicle synthesis and M. aeruginosa recruitment in Lake Rotorua.

year: 2016

title: Street-level bureaucracy and occupational therapy practices in Aotearoa New Zealand. A genealogical critique.

authors: Silcock, Elizabeth Mary

subjects: power

abstract: As a human science that is also part of administering and supporting bureaucracy, occupational therapy functions in multi-layered networks of power  that support many different social structures. Occupational therapists’ work often involves operationalising health, education and social services at the street-level, positioning them between the aspirations of both policy and social activism and material life outcomes. Through a genealogical critique, this thesis problematises the practice of occupational therapy through a Foucauldian lens that views everything as dangerous. By viewing occupational therapy practice as dangerous, the power relations at the street-level of the mundane and taken-for-granted have been problematised as part of much larger social structures of power and discourse. 
Several Foucauldian tools were deployed in order to ensure that a focus on occupational therapy practices was maintained; three distinct research methods were utilised to access a range of heterogeneous genealogical information.  Firstly, an historical archival analysis of the four iterations of the Competencies for Registration for occupational therapists document (1990 to the current day) produced by the regulatory authority, the Occupational Therapy Board of New Zealand, was carried out.  Secondly, practice observations of occupational therapists working in different practice settings were analysed as three individual case studies. Concurrently with these two methods, a critical action method using a research blog was developed to create a medium for public discussion of practice through an open engagement with the profession. The combination of these three methods enabled access to a range of elements for analysis.  Many of these elements inter-linked, overlapped and connected to historically contingent networks of dominant power that have formed through the processes of colonisation, the establishment of the health system and normalised medical practices, and economic forms of governance. The nuances of how occupational therapy is practised at the street-level offered opportunities to contest the dominance of these networks. In all three case studies there was an unspoken understanding and a normalisation of materiality as an accepted and significant element of how the profession practised.  The material regimes of knowledge and material practices in these unspoken norms were highly productive and able to contest other lines of power.  Along with this alternate network of power, the most recent version of the Competencies for Registration offers a further opportunity for occupational therapists to contest dominant power relations in a way that could capitalise on the secure position the profession has developed through its material network of power.  Opportunities for alternate pathways of practice which privilege Te Ao Māori and Te Tiriti o Waitangi are a possibility in the legally sanctioned Competencies. The close connection of occupational therapy practices to real life material outcomes for other people, position the street-level doing of occupational therapists at a juncture where action and decision making can re-configure power relations. Re-thinking practice in terms of what the doing of occupational therapy does in relation to networks of power, is an opportunity for practitioners to enact policy at the street-level in ways that use their ability to influence power from the bottom up whilst being alert to the dangers presented by doing so.

text: Street-level bureaucracy and occupational therapy practices in Aotearoa New Zealand. A genealogical critique. As a human science that is also part of administering and supporting bureaucracy, occupational therapy functions in multi-layered networks of power  that support many different social structures. Occupational therapists’ work often involves operationalising health, education and social services at the street-level, positioning them between the aspirations of both policy and social activism and material life outcomes. Through a genealogical critique, this thesis problematises the practice of occupational therapy through a Foucauldian lens that views everything as dangerous. By viewing occupational therapy practice as dangerous, the power relations at the street-level of the mundane and taken-for-granted have been problematised as part of much larger social structures of power and discourse. 
Several Foucauldian tools were deployed in order to ensure that a focus on occupational therapy practices was maintained; three distinct research methods were utilised to access a range of heterogeneous genealogical information.  Firstly, an historical archival analysis of the four iterations of the Competencies for Registration for occupational therapists document (1990 to the current day) produced by the regulatory authority, the Occupational Therapy Board of New Zealand, was carried out.  Secondly, practice observations of occupational therapists working in different practice settings were analysed as three individual case studies. Concurrently with these two methods, a critical action method using a research blog was developed to create a medium for public discussion of practice through an open engagement with the profession. The combination of these three methods enabled access to a range of elements for analysis.  Many of these elements inter-linked, overlapped and connected to historically contingent networks of dominant power that have formed through the processes of colonisation, the establishment of the health system and normalised medical practices, and economic forms of governance. The nuances of how occupational therapy is practised at the street-level offered opportunities to contest the dominance of these networks. In all three case studies there was an unspoken understanding and a normalisation of materiality as an accepted and significant element of how the profession practised.  The material regimes of knowledge and material practices in these unspoken norms were highly productive and able to contest other lines of power.  Along with this alternate network of power, the most recent version of the Competencies for Registration offers a further opportunity for occupational therapists to contest dominant power relations in a way that could capitalise on the secure position the profession has developed through its material network of power.  Opportunities for alternate pathways of practice which privilege Te Ao Māori and Te Tiriti o Waitangi are a possibility in the legally sanctioned Competencies. The close connection of occupational therapy practices to real life material outcomes for other people, position the street-level doing of occupational therapists at a juncture where action and decision making can re-configure power relations. Re-thinking practice in terms of what the doing of occupational therapy does in relation to networks of power, is an opportunity for practitioners to enact policy at the street-level in ways that use their ability to influence power from the bottom up whilst being alert to the dangers presented by doing so.

year: 2018