title: The effects of velocity and nitrate on Phormidium accrual cycles: a stream mesocosm experiment

authors: McAllister, Tara G.

subjects: Science & Technology

abstract: Proliferations of benthic cyanobacteria in the genus Phormidium are a global concern because of their increasing prevalence and ability to produce harmful toxins. Most studies have been observational and have linked physicochemical variables to Phormidium cover measured at the reach scale. Authors of these studies have alluded to nutrients and flow as key factors in accrual. Our goal was to use an experimental approach to examine how changes in velocity and NO₃⁻ concentrations influence Phormidium accrual. We hypothesized that: 1) Phormidium biomass accrual would be positively correlated with stream velocity; 2) biomass accrual would be positively related to NO₃⁻  concentration, which would have a stronger effect during early accrual; 3) an NO₃⁻  ✕ velocity interaction would arise from saturation of accrual at high NO₃⁻  and high velocity; and 4) the probability of detachment would increase with decreasing velocity. We assessed mat expansion, biomass (as phycoerythrin and chlorophyll a [Chl a] concentrations, and biovolume), and algal assemblage composition in flow-through channel mesocosms for 16 d. We crossed 2 velocity treatments (0.1 and 0.2 m/s, slow and fast, respectively) with 3 NO₃⁻ treatments (0.02, 0.1, and 0.4 mg/L, ambient, medium, and high, respectively). Velocity was positively correlated with all measures of Phormidium biomass, but patch expansion rates increased at similar rates across all treatments. NO₃⁻ had no effect during early accrual, but phycoerythrin concentrations increased with increasing NO₃⁻  in fast-velocity treatments. At the end of the experiment, patch size was greater in the high-velocity treatments because of a greater number of partial or full patch detachments in slow-velocity treatments. These results suggest that NO₃⁻  concentrations do not affect Phormidium expansion and detachment, but may be important during colonization (not investigated), and that mat expansion occurs at a similar rate regardless of velocity, but termination of accrual cycles occurs earlier in slow velocities.

text: The effects of velocity and nitrate on Phormidium accrual cycles: a stream mesocosm experiment Proliferations of benthic cyanobacteria in the genus Phormidium are a global concern because of their increasing prevalence and ability to produce harmful toxins. Most studies have been observational and have linked physicochemical variables to Phormidium cover measured at the reach scale. Authors of these studies have alluded to nutrients and flow as key factors in accrual. Our goal was to use an experimental approach to examine how changes in velocity and NO₃⁻ concentrations influence Phormidium accrual. We hypothesized that: 1) Phormidium biomass accrual would be positively correlated with stream velocity; 2) biomass accrual would be positively related to NO₃⁻  concentration, which would have a stronger effect during early accrual; 3) an NO₃⁻  ✕ velocity interaction would arise from saturation of accrual at high NO₃⁻  and high velocity; and 4) the probability of detachment would increase with decreasing velocity. We assessed mat expansion, biomass (as phycoerythrin and chlorophyll a [Chl a] concentrations, and biovolume), and algal assemblage composition in flow-through channel mesocosms for 16 d. We crossed 2 velocity treatments (0.1 and 0.2 m/s, slow and fast, respectively) with 3 NO₃⁻ treatments (0.02, 0.1, and 0.4 mg/L, ambient, medium, and high, respectively). Velocity was positively correlated with all measures of Phormidium biomass, but patch expansion rates increased at similar rates across all treatments. NO₃⁻ had no effect during early accrual, but phycoerythrin concentrations increased with increasing NO₃⁻  in fast-velocity treatments. At the end of the experiment, patch size was greater in the high-velocity treatments because of a greater number of partial or full patch detachments in slow-velocity treatments. These results suggest that NO₃⁻  concentrations do not affect Phormidium expansion and detachment, but may be important during colonization (not investigated), and that mat expansion occurs at a similar rate regardless of velocity, but termination of accrual cycles occurs earlier in slow velocities.

year: 2018

title: Points of tension and possibility: Boundaries in and of physical education

authors: Penney, Dawn

subjects: Assessment

abstract: This article offers a conceptually based commentary that addresses a longstanding dilemma for physical education, of what theoretical insights can usefully be pursued as a basis for advancing physical education curriculum, pedagogy and assessment. It utilises the work of Basil Bernstein to argue that structural and symbolic boundaries are key to understanding and productively engaging with stability and change in physical education. Relations between curriculum, pedagogy and assessment are examined in terms of their linkages with legitimate knowledge structures and knowledge relations in/of physical education, and in turn, with equity in physical education. While curriculum, pedagogy and assessment are each identified as important avenues for critically informed pedagogic action, the collective dynamic is identified as over-riding any single influence. Furthermore, that dynamic is shown to be inseparable from the knowledge structures in/of physical education.

text: Points of tension and possibility: Boundaries in and of physical education This article offers a conceptually based commentary that addresses a longstanding dilemma for physical education, of what theoretical insights can usefully be pursued as a basis for advancing physical education curriculum, pedagogy and assessment. It utilises the work of Basil Bernstein to argue that structural and symbolic boundaries are key to understanding and productively engaging with stability and change in physical education. Relations between curriculum, pedagogy and assessment are examined in terms of their linkages with legitimate knowledge structures and knowledge relations in/of physical education, and in turn, with equity in physical education. While curriculum, pedagogy and assessment are each identified as important avenues for critically informed pedagogic action, the collective dynamic is identified as over-riding any single influence. Furthermore, that dynamic is shown to be inseparable from the knowledge structures in/of physical education.

year: 2013

title: A 'class of no political weight'? Interracial marriage, mixed race children and land rights in southern New Zealand, 1840s-1880s

authors: Wanhalla, Angela

subjects: Social Sciences

abstract: Interracial marriage was a defining feature of interaction between local Ngāi Tahu and newcomers in southern New Zealand from the early nineteenth century. Scholarship has explored the importance of such relationships to development of New Zealand’s early resource-based economies and to colonial assimilation policies. However, the experiences of cross-cultural households and families in colonial New Zealand are less well documented.

Using a body of writing produced by fathers and their mixed-race children in response to land claims investigations in the mid-nineteenth century, this article explores the political, economic and social world of interracial families in southern New Zealand. The correspondence over land rights reveals the ongoing importance of kinship ties through generations as colonial expansion impinged on these communities. Through petitioning and letter writing, fathers and children contested what marriage and family meant and strategically asserted their individual and collective identity in the face of increasing land dispossession and economic hardship.

text: A 'class of no political weight'? Interracial marriage, mixed race children and land rights in southern New Zealand, 1840s-1880s Interracial marriage was a defining feature of interaction between local Ngāi Tahu and newcomers in southern New Zealand from the early nineteenth century. Scholarship has explored the importance of such relationships to development of New Zealand’s early resource-based economies and to colonial assimilation policies. However, the experiences of cross-cultural households and families in colonial New Zealand are less well documented.

Using a body of writing produced by fathers and their mixed-race children in response to land claims investigations in the mid-nineteenth century, this article explores the political, economic and social world of interracial families in southern New Zealand. The correspondence over land rights reveals the ongoing importance of kinship ties through generations as colonial expansion impinged on these communities. Through petitioning and letter writing, fathers and children contested what marriage and family meant and strategically asserted their individual and collective identity in the face of increasing land dispossession and economic hardship.

year: 2019