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: Research methods in psychology (Aotearoa New Zealand edition)

authors: Price, Paul C.

abstract: Psychology has its own set of tools to investigate the important research questions of its field. Psychology is a relatively new field with methods and practices that are evolving at a rapid rate. With this textbook, we introduce students to the fundamental principles of what it is like to think like a psychology researcher. In recent years, the conversation in psychology has shifted to an introspective one, re-examining the knowledge that we consider foundational. As many introspective conversations do, this one caused a crisis of faith. Psychologists are questioning if we really know what we thought we knew or if we simply got lucky. We are struggling with understanding our publication biases and the training that we provide our students. Instead of shying away from this controversy, this textbook invites the reader to step right into the middle of it. With every step of the way, the research process in psychology is fraught with decisions, trade-offs, and uncertainty. It is not an easy route to traverse, but we hope this textbook will be a roadmap that can inspire the direction if not give absolute instructions. As the field grapples with its identity, we will use better tools, more transparent practices, and more open conversations to improve our understanding of human behaviour.

text: Research methods in psychology (Aotearoa New Zealand edition) Psychology has its own set of tools to investigate the important research questions of its field. Psychology is a relatively new field with methods and practices that are evolving at a rapid rate. With this textbook, we introduce students to the fundamental principles of what it is like to think like a psychology researcher. In recent years, the conversation in psychology has shifted to an introspective one, re-examining the knowledge that we consider foundational. As many introspective conversations do, this one caused a crisis of faith. Psychologists are questioning if we really know what we thought we knew or if we simply got lucky. We are struggling with understanding our publication biases and the training that we provide our students. Instead of shying away from this controversy, this textbook invites the reader to step right into the middle of it. With every step of the way, the research process in psychology is fraught with decisions, trade-offs, and uncertainty. It is not an easy route to traverse, but we hope this textbook will be a roadmap that can inspire the direction if not give absolute instructions. As the field grapples with its identity, we will use better tools, more transparent practices, and more open conversations to improve our understanding of human behaviour.

year: 2020

title: Kei ō tātou ringa te rongoa? Is the remedy already at hand?
The assertion and application of tikanga as a valid and credible response to contemporary issues.

authors: Taitoko, Mikaere

subjects: tikanga

abstract: This thesis examines the notion that tikanga is well positioned to address issues confronting Māori and other indigenous groups who strive to achieve self-determination and the freedom to be and to do.  This work is inspired by the late John Te Rangi-āniwaniwa Rangihau’s statement, “Ko te rongoā kei roto i ō tātau ringa” (1987, p. 24), which promotes the notion that through culture and identity Māori already have within their grasp the answers to contemporary matters of import in te ao Māori.  This thesis inverts that statement and presents it as a question querying whether indeed the remedy is at hand and, if so, could tikanga and cultural identity be that remedy.  To that end this study deliberately sets out to examine if the rongoa of self-determination, power and freedom can be achieved by the assertion and application of Māori ways of being and doing, that is to say by exercising tikanga.
Understanding notions of tikanga, sovereignty, and indigeneity is pivotal to this study as is articulating the notion of third space.  This thesis argues that these four notions are interconnected when considering ideas of self-determination for disempowered groups.  A case study forms a large part of this work and focuses on an indigenous group operating from a pre-contact tupuna worldview and based on He Whakaputanga o te Rangatiratanga o Nu Tireni 1835/Declaration of Independence of New Zealand 1835.  This particular group was chosen because it presented as being a point of intersect for the four notions of tikanga, sovereignty, indigeneity and the third space.
This thesis argues that whilst tikanga is a powerful mechanism for determining and rationalising ways of being and doing it has less to offer at a pragmatic level when it comes to effecting change in the status quo.  However, when overlaid with the third space lens new perspectives can be enunciated and new opportunities detected which in turn can lead to determining new actions.  Through this study it becomes clear that the assertion and application of tikanga contributes to, but on its own is not, the whole answer.

text: Kei ō tātou ringa te rongoa? Is the remedy already at hand?
The assertion and application of tikanga as a valid and credible response to contemporary issues. This thesis examines the notion that tikanga is well positioned to address issues confronting Māori and other indigenous groups who strive to achieve self-determination and the freedom to be and to do.  This work is inspired by the late John Te Rangi-āniwaniwa Rangihau’s statement, “Ko te rongoā kei roto i ō tātau ringa” (1987, p. 24), which promotes the notion that through culture and identity Māori already have within their grasp the answers to contemporary matters of import in te ao Māori.  This thesis inverts that statement and presents it as a question querying whether indeed the remedy is at hand and, if so, could tikanga and cultural identity be that remedy.  To that end this study deliberately sets out to examine if the rongoa of self-determination, power and freedom can be achieved by the assertion and application of Māori ways of being and doing, that is to say by exercising tikanga.
Understanding notions of tikanga, sovereignty, and indigeneity is pivotal to this study as is articulating the notion of third space.  This thesis argues that these four notions are interconnected when considering ideas of self-determination for disempowered groups.  A case study forms a large part of this work and focuses on an indigenous group operating from a pre-contact tupuna worldview and based on He Whakaputanga o te Rangatiratanga o Nu Tireni 1835/Declaration of Independence of New Zealand 1835.  This particular group was chosen because it presented as being a point of intersect for the four notions of tikanga, sovereignty, indigeneity and the third space.
This thesis argues that whilst tikanga is a powerful mechanism for determining and rationalising ways of being and doing it has less to offer at a pragmatic level when it comes to effecting change in the status quo.  However, when overlaid with the third space lens new perspectives can be enunciated and new opportunities detected which in turn can lead to determining new actions.  Through this study it becomes clear that the assertion and application of tikanga contributes to, but on its own is not, the whole answer.

year: 2013