title: Spatial and temporal trends of phytoplankton and physiochemical variables in a hypertrophic, monomictic lake

authors: Simmonds, Bernard Michael

subjects: Phytoplankton

abstract: Spatial and temporal variations in the physical, chemical and biological composition of Lake Ōkaro were measured over 16 months. Lake Ōkaro is a small (0.32 km2) hypertrophic, monomictic lake located in the Central Volcanic Zone of the North Island, New Zealand. Vertical profiles of temperature, chlorophyll fluorescence, dissolved oxygen concentration (DO), pH, specific conductance, photosynthetically active radiation (PAR) and nutrient species, including ammonium-nitrogen (NH4-N), nitrite-nitrogen (NO2-N), nitrate-nitrogen (NO3-N) and phosphate-phosphorus (PO4-P), were collected at up to nine stations at weekly to monthly frequencies. High-frequency variability was assessed during two separate 24-hour monitoring periods, coinciding with an Anabaena spiroides-dominated surface bloom, and a Ceratium hirundinella-dominated deep chlorophyll maximum. Additional data for wind direction and velocity, incident solar irradiance and rainfall was sourced from a meteorological weather station and a lake monitoring buoy at Rotorua, 20 km north of the lake. Spatial variability was more pronounced during summer. Observed vertical gradients in chlorophyll fluorescence, DO, specific conductance and nutrient species were closely linked to thermal stability of the water column. There were large variations in chlorophyll fluorescence amongst stations in summer, which related to displacement of the metalimnion and associated changes in chlorophyll fluorescence. Winter mixing was characterised by relative homogeneity of the water column. Nutrient concentrations were elevated at all depths whereas high concentrations had previously been confined to lower depth strata (the hypolimnion). Temperature profiles in summer displayed clear vertical gradients with a well-defined metalimnion that increased in depth until winter mixing generated isothermal conditions. Chlorophyll fluorescence profiles were characterised by the formation of a DCM that was recurrent over both summer periods, and was strongly statistically related to the depth of the thermocline for the duration of stratification. Dissolved oxygen, specific conductance and pH were relatively uniform horizontally, though pH was consistently lower at a well-sheltered near-shore station. All variables showed strong variations with depth during the stratified period. Dissolved oxygen was negligible or zero below the thermocline for much of the stratified period while specific conductance was lowest above or at the thermocline. There were also strong vertical gradients in nutrient concentrations in summer, with concentrations below the thermocline often an order of magnitude higher than those above. The representativeness of fluorescence at a central station to a whole-lake scale was assessed using a vertical integrated value and the standard error derived from up to eight other stations. Values at the single station frequently deviated from the mean fluorescence of the wider lake, particularly at the DCM which suggests that extrapolating single-station measurements to a whole lake could provide highly exaggerated values of lake fluorescence. High-frequency sampling during the A. spiroides-dominated surface bloom showed diel temperature variations attributed mostly to solar irradiance. There was high light attenuation from the high phytoplankton biomass and consistently elevated pH and DO. Fluorescence profiles suggested that the phytoplankton population was strongly buoyant and did not undergo diel vertical migration. High-frequency sampling during a period when there was a dinoflagellate-dominated DCM showed two coinciding fluorescence peaks had formed at 6-7 and 7-8 m depth and contained morphologically and physiologically distinct taxa. The 6-7 m DCM was predominantly Ceratium hirundinella, while the 7-8 m DCM was composed of C. hirundinella and unidentified colonial picoplankton. Fluorescence profiles suggested diel vertical migration was not taking place, and strong gradients in light, nutrient availability and the relative biomass of the dominants suggested that the 6-7 and 7-8 m DCM populations potentially differed in their modes of nutrition, light history and susceptibility to grazing. This research illustrates the degree of spatial variability that can exist in a small, monomictic hypertrophic lake at a given time, and highlights some of the potential limitations of using single-site monitoring stations to represent the physical, chemical and biological conditions of a whole lake. This information may be used to critically evaluate the reliability of phytoplankton biomass estimates that have been derived from spatially-limited sampling methods. This study further illustrates the role that thermal stratification plays in creating vertical gradients in a number of biological and chemical variables, and demonstrates that parallels exist with regard to DCM formation in oligotrophic and hypertrophic lakes, relating to the interplay between light, chlorophyll fluorescence and thermal stratification. Evidence is also provided showing that diel-scale variations in phytoplankton biomass can differ markedly between a cyanobacteria-dominated surface bloom and a dinoflagellate-dominated DCM, which further highlights the value of high-frequency sampling when seeking to estimate phytoplankton biomass using in situ methods.

text: Spatial and temporal trends of phytoplankton and physiochemical variables in a hypertrophic, monomictic lake Spatial and temporal variations in the physical, chemical and biological composition of Lake Ōkaro were measured over 16 months. Lake Ōkaro is a small (0.32 km2) hypertrophic, monomictic lake located in the Central Volcanic Zone of the North Island, New Zealand. Vertical profiles of temperature, chlorophyll fluorescence, dissolved oxygen concentration (DO), pH, specific conductance, photosynthetically active radiation (PAR) and nutrient species, including ammonium-nitrogen (NH4-N), nitrite-nitrogen (NO2-N), nitrate-nitrogen (NO3-N) and phosphate-phosphorus (PO4-P), were collected at up to nine stations at weekly to monthly frequencies. High-frequency variability was assessed during two separate 24-hour monitoring periods, coinciding with an Anabaena spiroides-dominated surface bloom, and a Ceratium hirundinella-dominated deep chlorophyll maximum. Additional data for wind direction and velocity, incident solar irradiance and rainfall was sourced from a meteorological weather station and a lake monitoring buoy at Rotorua, 20 km north of the lake. Spatial variability was more pronounced during summer. Observed vertical gradients in chlorophyll fluorescence, DO, specific conductance and nutrient species were closely linked to thermal stability of the water column. There were large variations in chlorophyll fluorescence amongst stations in summer, which related to displacement of the metalimnion and associated changes in chlorophyll fluorescence. Winter mixing was characterised by relative homogeneity of the water column. Nutrient concentrations were elevated at all depths whereas high concentrations had previously been confined to lower depth strata (the hypolimnion). Temperature profiles in summer displayed clear vertical gradients with a well-defined metalimnion that increased in depth until winter mixing generated isothermal conditions. Chlorophyll fluorescence profiles were characterised by the formation of a DCM that was recurrent over both summer periods, and was strongly statistically related to the depth of the thermocline for the duration of stratification. Dissolved oxygen, specific conductance and pH were relatively uniform horizontally, though pH was consistently lower at a well-sheltered near-shore station. All variables showed strong variations with depth during the stratified period. Dissolved oxygen was negligible or zero below the thermocline for much of the stratified period while specific conductance was lowest above or at the thermocline. There were also strong vertical gradients in nutrient concentrations in summer, with concentrations below the thermocline often an order of magnitude higher than those above. The representativeness of fluorescence at a central station to a whole-lake scale was assessed using a vertical integrated value and the standard error derived from up to eight other stations. Values at the single station frequently deviated from the mean fluorescence of the wider lake, particularly at the DCM which suggests that extrapolating single-station measurements to a whole lake could provide highly exaggerated values of lake fluorescence. High-frequency sampling during the A. spiroides-dominated surface bloom showed diel temperature variations attributed mostly to solar irradiance. There was high light attenuation from the high phytoplankton biomass and consistently elevated pH and DO. Fluorescence profiles suggested that the phytoplankton population was strongly buoyant and did not undergo diel vertical migration. High-frequency sampling during a period when there was a dinoflagellate-dominated DCM showed two coinciding fluorescence peaks had formed at 6-7 and 7-8 m depth and contained morphologically and physiologically distinct taxa. The 6-7 m DCM was predominantly Ceratium hirundinella, while the 7-8 m DCM was composed of C. hirundinella and unidentified colonial picoplankton. Fluorescence profiles suggested diel vertical migration was not taking place, and strong gradients in light, nutrient availability and the relative biomass of the dominants suggested that the 6-7 and 7-8 m DCM populations potentially differed in their modes of nutrition, light history and susceptibility to grazing. This research illustrates the degree of spatial variability that can exist in a small, monomictic hypertrophic lake at a given time, and highlights some of the potential limitations of using single-site monitoring stations to represent the physical, chemical and biological conditions of a whole lake. This information may be used to critically evaluate the reliability of phytoplankton biomass estimates that have been derived from spatially-limited sampling methods. This study further illustrates the role that thermal stratification plays in creating vertical gradients in a number of biological and chemical variables, and demonstrates that parallels exist with regard to DCM formation in oligotrophic and hypertrophic lakes, relating to the interplay between light, chlorophyll fluorescence and thermal stratification. Evidence is also provided showing that diel-scale variations in phytoplankton biomass can differ markedly between a cyanobacteria-dominated surface bloom and a dinoflagellate-dominated DCM, which further highlights the value of high-frequency sampling when seeking to estimate phytoplankton biomass using in situ methods.

year: 2011

title: Examining neuroplasticity as a function of errors during motor learning

authors: Nirol

abstract: Proficient motor learning is important for both athletes looking to improve their performance and patients learning daily living skills. Research has identified different methods for learning motor skills, focusing on two types: implicit and explicit learning. Implicit learning happens with little awareness, while explicit learning requires more conscious thought. Studies show that implicit learning is often more effective because it uses less mental effort and is more reliable under stress. This might be due to stronger neural connections in the brain formed during implicit learning. However, it is unclear whether implicit learning leads to more brain changes, known as neuroplasticity, than explicit learning. Neuroplasticity is the brain's ability to adapt and form new memory networks in response to experiences. This study aims to investigate differences in neuroplastic changes resulting from implicit versus explicit learning of a traditional Dutch shuffleboard game (Sjoelbak). We used baseline electroencephalography (EEG) to measure changes in brain activity before and after practice to assess neuroplasticity. We examined the effects of errorless and errorful learning protocols on task performance and neural connectivity. Both strategies improved accuracy from pretest to posttest, indicating effective skill acquisition. However, participants struggled to transfer skills to new contexts, as shown by decreased performance in the transfer test. Despite expectations of greater neuroplastic changes as a function of errorless learning, resting-state beta connectivity analyses showed no significant interactions. However, no significant differences were evident in the overall error rates between the groups during the learning phase, suggesting that implicit motor learning may not have occurred for the errorless learning condition. This suggests that neural adaptations are more complex than initially hypothesized.

text: Examining neuroplasticity as a function of errors during motor learning Proficient motor learning is important for both athletes looking to improve their performance and patients learning daily living skills. Research has identified different methods for learning motor skills, focusing on two types: implicit and explicit learning. Implicit learning happens with little awareness, while explicit learning requires more conscious thought. Studies show that implicit learning is often more effective because it uses less mental effort and is more reliable under stress. This might be due to stronger neural connections in the brain formed during implicit learning. However, it is unclear whether implicit learning leads to more brain changes, known as neuroplasticity, than explicit learning. Neuroplasticity is the brain's ability to adapt and form new memory networks in response to experiences. This study aims to investigate differences in neuroplastic changes resulting from implicit versus explicit learning of a traditional Dutch shuffleboard game (Sjoelbak). We used baseline electroencephalography (EEG) to measure changes in brain activity before and after practice to assess neuroplasticity. We examined the effects of errorless and errorful learning protocols on task performance and neural connectivity. Both strategies improved accuracy from pretest to posttest, indicating effective skill acquisition. However, participants struggled to transfer skills to new contexts, as shown by decreased performance in the transfer test. Despite expectations of greater neuroplastic changes as a function of errorless learning, resting-state beta connectivity analyses showed no significant interactions. However, no significant differences were evident in the overall error rates between the groups during the learning phase, suggesting that implicit motor learning may not have occurred for the errorless learning condition. This suggests that neural adaptations are more complex than initially hypothesized.

year: 2025

title: Possibilities of transformation: discourses of difference in organisational communication

authors: Jones, Deborah Helen

abstract: In this thesis I set out to create an interdisciplinary location from which to address the relationship between gender and communication in an organisational context. I draw on feminist and post-structuralist theory to ask the question: How is ‘difference’ constructed in organisational communication? I use the term ‘difference’ here to indicate that I am interested in how ‘gender’ works in relationship with other kinds of difference, especially in relation to ethnic difference.

My thesis is intended as a contribution to feminist communication theory, and specifically, to the emerging field of feminist organisational communication. Because of the approach I take to ‘communication’, this project addresses broad issues of identity, agency and discourse in organisations. In this sense, I also see the thesis as a contribution to organisational studies, and particularly to the study of organisational discourse, which opens up new relationships between ‘organisation’ and ‘communication’. Interdisciplinarity itself is a key issue in my thesis, as I set out to create connections between disciplinary fields in the service of contesting them, rather than seeking to create new boundaries. A second key focus is the development of theoretical sophistication in the field of gender and communication. I draw on feminist/post-structuralist theory, especially feminist readings of Michel Foucault’s work to generate this development. My third key focus is the issue of agency, which I see as central to theorising organisational transformation, and also as central to re-thinking communication theory.

My writing strategies demonstrate my commitments to reflexivity in developing feminist/post-structuralist research epistemologies, and I experiment with ways of paying attention to issues of authority throughout the thesis. This thesis is divided into two main parts. In Chapters 2 to 6, I set up a theoretical framework for feminist/post-structuralist accounts of gender and ethnicity, and weave this theory through the literatures of ‘gender and communication’, ‘cross-cultural communication’, and ‘organisational communication’. I set out to produce an ‘autocritique’, an opportunity to draw on developments in post-structuralist theory to think differently about feminist ‘organisational communication’, putting it within a broader framework of ‘difference’.

In the second part of the thesis, Chapters 7 to 12, I put issues generated by this theoretical framework in a specific organisational context, asking: How are gender and ethnic differences constructed in the discourses of Equal Employment Opportunities (EEO) and Biculturalism in New Zealand government organisations? Chapters 7 and 8 introduce my field studies methodology and research subjects, and provide background narratives which frame the historical and cultural context in which they were carried out. In Chapters 9 to 12 I carry out a discourse analysis of interviews with EEO and Biculturalism practitioners, and also analyse published and unpublished documents associated with ‘difference’ in employment policies. These accounts of field studies are intended as a series of experiments with theorising ‘organisational communication’ in different ways. I complete the thesis with a ‘Review’ (Chapter 13) in which I reflect on key theoretical threads, and on further questions that emerged during the project.

text: Possibilities of transformation: discourses of difference in organisational communication In this thesis I set out to create an interdisciplinary location from which to address the relationship between gender and communication in an organisational context. I draw on feminist and post-structuralist theory to ask the question: How is ‘difference’ constructed in organisational communication? I use the term ‘difference’ here to indicate that I am interested in how ‘gender’ works in relationship with other kinds of difference, especially in relation to ethnic difference.

My thesis is intended as a contribution to feminist communication theory, and specifically, to the emerging field of feminist organisational communication. Because of the approach I take to ‘communication’, this project addresses broad issues of identity, agency and discourse in organisations. In this sense, I also see the thesis as a contribution to organisational studies, and particularly to the study of organisational discourse, which opens up new relationships between ‘organisation’ and ‘communication’. Interdisciplinarity itself is a key issue in my thesis, as I set out to create connections between disciplinary fields in the service of contesting them, rather than seeking to create new boundaries. A second key focus is the development of theoretical sophistication in the field of gender and communication. I draw on feminist/post-structuralist theory, especially feminist readings of Michel Foucault’s work to generate this development. My third key focus is the issue of agency, which I see as central to theorising organisational transformation, and also as central to re-thinking communication theory.

My writing strategies demonstrate my commitments to reflexivity in developing feminist/post-structuralist research epistemologies, and I experiment with ways of paying attention to issues of authority throughout the thesis. This thesis is divided into two main parts. In Chapters 2 to 6, I set up a theoretical framework for feminist/post-structuralist accounts of gender and ethnicity, and weave this theory through the literatures of ‘gender and communication’, ‘cross-cultural communication’, and ‘organisational communication’. I set out to produce an ‘autocritique’, an opportunity to draw on developments in post-structuralist theory to think differently about feminist ‘organisational communication’, putting it within a broader framework of ‘difference’.

In the second part of the thesis, Chapters 7 to 12, I put issues generated by this theoretical framework in a specific organisational context, asking: How are gender and ethnic differences constructed in the discourses of Equal Employment Opportunities (EEO) and Biculturalism in New Zealand government organisations? Chapters 7 and 8 introduce my field studies methodology and research subjects, and provide background narratives which frame the historical and cultural context in which they were carried out. In Chapters 9 to 12 I carry out a discourse analysis of interviews with EEO and Biculturalism practitioners, and also analyse published and unpublished documents associated with ‘difference’ in employment policies. These accounts of field studies are intended as a series of experiments with theorising ‘organisational communication’ in different ways. I complete the thesis with a ‘Review’ (Chapter 13) in which I reflect on key theoretical threads, and on further questions that emerged during the project.

year: 1998