title: Phytoplankton nutrient limitation in Lake Rotorua

authors: Tempero, Grant Wayne

abstract: Lake Rotorua is one of 12 lakes jointly managed by the Rotorua Lakes Council, Te Arawa Lakes Trust and the Bay of Plenty Regional Council under the Rotorua Te Arawa Lakes Programme. The lake is currently classified as eutrophic and a Trophic Lake Index (TLI) value of 4.2 has been set as an integrated target for lake water quality. A number of catchment and lake management strategies have been implemented to achieve the targeted TLI including land use changes, wetland enhancement, lake weed harvesting, sediment detainment bunds, sewage reticulation and alum dosing. Alum (aluminium sulphate) is commonly applied to freshwater and wastewater systems to remove phosphorus, reducing its availability for phytoplankton growth. The initiation of alum dosing to the Utuhina Stream in 2006 and the Puarenga Stream in 2010 was associated with a significant decline in water column dissolved reactive phosphorus (DRP) and improvements in water quality of Lake Rotorua. 
The use of alum to control external and internal phosphorus loading has been identified as key component in the restoration of Lake Rotorua and recently observed improvements in water quality suggest that the lake could be transitioning to a more phosphorus limited state. Determination of phytoplankton nutrient limitation in Lake Rotorua was identified as a priority through the 2017 Plan Change 10 Science Review. An initial seasonal nutrient limitation study was carried out in 2019 with nutrient limitation assays conducted at 3-monthly intervals over the course of the year. Nitrogen limitation was indicated for the March assay and nutrient co-limitation for the December period, but results for the winter and spring periods were inconclusive. There has also been increasing recognition that nutrient availability in limnetic systems may vary in response to seasonal changes in external and external loading and even to isolated storm events. 
The University of Waikato was contracted to investigate potential changes in nutrient limitation within Lake Rotorua at sub-monthly time-scales, and to determine if alum dose rates could be optimised to take advantage of periods of phosphorus limitation. Phytoplankton nutrient limitation growth assays were conducted on a fortnightly basis from mid-October 2020 to May 2021. In addition to determination of lake surface nutrient and chlorophyll a concentrations, triplicate 1 L phytoplankton samples were spiked with either phosphorus (0.1 mg-P L⁻¹), nitrogen (1 mg-N L⁻¹) or phosphorus (0.1 mg-P L⁻¹) and nitrogen (1 mg-N L⁻¹) and incubated for 5-days under a single light intensity of 100 μmol m⁻²s⁻¹ PAR at lake surface temperature and photoperiod. Phytoplankton growth responses were measured as comparative chlorophyll a, comparative biomass and net biomass growth. Summarised results from the 16 assays along with the predicted nutrient state from the stoichiometric mass ratio of TN:TP are presented in the table below. 
Under the test conditions nitrogen limitation was indicated for most of the summer months (December–March) and nutrient co-limitation during the spring and late autumn. Only short (~2 weeks) periods of P-limitation were observed, one of which was associated with an intensive storm event at the end of March. These seasonal fluctuations in nitrogen and phosphorus supply are similar to those observed in other temperate limnetic systems. In the spring, external nitrogen and phosphorus loading is high, then decline in the summer as rainfall and associated inflows wane. During the summer, internal loading becomes more important in polymictic lakes due to repeated internal nutrient cycling from stratification and mixing events. This results in phosphorus limitation in the spring, transitioning to nitrogen limitation or colimitation (primarily nitrogen) in the summer, and then returning to phosphorus/colimitation during the winter due to increased nitrogen-loading from the catchment from increased catchment discharge. 
Due to the modest periods of phosphorus limitation indicated by the assays, there appears to be little potential for optimisation of alum dose rates in order capitalise on natural periods of phosphorus limitation. Further, changes in phytoplankton community composition and abundance appear to be more strongly driven by physical environmental factors such as temperature, light and wind speed, than nutrient availability. Although alum dosing is effective in removing DRP from the Utuhina and Puarenga inflows, its assumed effectiveness in reducing internal phosphorus loading in Lake Rotorua requires further evaluation.

text: Phytoplankton nutrient limitation in Lake Rotorua Lake Rotorua is one of 12 lakes jointly managed by the Rotorua Lakes Council, Te Arawa Lakes Trust and the Bay of Plenty Regional Council under the Rotorua Te Arawa Lakes Programme. The lake is currently classified as eutrophic and a Trophic Lake Index (TLI) value of 4.2 has been set as an integrated target for lake water quality. A number of catchment and lake management strategies have been implemented to achieve the targeted TLI including land use changes, wetland enhancement, lake weed harvesting, sediment detainment bunds, sewage reticulation and alum dosing. Alum (aluminium sulphate) is commonly applied to freshwater and wastewater systems to remove phosphorus, reducing its availability for phytoplankton growth. The initiation of alum dosing to the Utuhina Stream in 2006 and the Puarenga Stream in 2010 was associated with a significant decline in water column dissolved reactive phosphorus (DRP) and improvements in water quality of Lake Rotorua. 
The use of alum to control external and internal phosphorus loading has been identified as key component in the restoration of Lake Rotorua and recently observed improvements in water quality suggest that the lake could be transitioning to a more phosphorus limited state. Determination of phytoplankton nutrient limitation in Lake Rotorua was identified as a priority through the 2017 Plan Change 10 Science Review. An initial seasonal nutrient limitation study was carried out in 2019 with nutrient limitation assays conducted at 3-monthly intervals over the course of the year. Nitrogen limitation was indicated for the March assay and nutrient co-limitation for the December period, but results for the winter and spring periods were inconclusive. There has also been increasing recognition that nutrient availability in limnetic systems may vary in response to seasonal changes in external and external loading and even to isolated storm events. 
The University of Waikato was contracted to investigate potential changes in nutrient limitation within Lake Rotorua at sub-monthly time-scales, and to determine if alum dose rates could be optimised to take advantage of periods of phosphorus limitation. Phytoplankton nutrient limitation growth assays were conducted on a fortnightly basis from mid-October 2020 to May 2021. In addition to determination of lake surface nutrient and chlorophyll a concentrations, triplicate 1 L phytoplankton samples were spiked with either phosphorus (0.1 mg-P L⁻¹), nitrogen (1 mg-N L⁻¹) or phosphorus (0.1 mg-P L⁻¹) and nitrogen (1 mg-N L⁻¹) and incubated for 5-days under a single light intensity of 100 μmol m⁻²s⁻¹ PAR at lake surface temperature and photoperiod. Phytoplankton growth responses were measured as comparative chlorophyll a, comparative biomass and net biomass growth. Summarised results from the 16 assays along with the predicted nutrient state from the stoichiometric mass ratio of TN:TP are presented in the table below. 
Under the test conditions nitrogen limitation was indicated for most of the summer months (December–March) and nutrient co-limitation during the spring and late autumn. Only short (~2 weeks) periods of P-limitation were observed, one of which was associated with an intensive storm event at the end of March. These seasonal fluctuations in nitrogen and phosphorus supply are similar to those observed in other temperate limnetic systems. In the spring, external nitrogen and phosphorus loading is high, then decline in the summer as rainfall and associated inflows wane. During the summer, internal loading becomes more important in polymictic lakes due to repeated internal nutrient cycling from stratification and mixing events. This results in phosphorus limitation in the spring, transitioning to nitrogen limitation or colimitation (primarily nitrogen) in the summer, and then returning to phosphorus/colimitation during the winter due to increased nitrogen-loading from the catchment from increased catchment discharge. 
Due to the modest periods of phosphorus limitation indicated by the assays, there appears to be little potential for optimisation of alum dose rates in order capitalise on natural periods of phosphorus limitation. Further, changes in phytoplankton community composition and abundance appear to be more strongly driven by physical environmental factors such as temperature, light and wind speed, than nutrient availability. Although alum dosing is effective in removing DRP from the Utuhina and Puarenga inflows, its assumed effectiveness in reducing internal phosphorus loading in Lake Rotorua requires further evaluation.

year: 2022

title: Editorial

authors: Clarkin-Phillips, Jeanette

abstract: As New Zealand contemplates wholesale review of the formal schooling system and the leadership implications thereof, the winds of educational change begin to swirl. Not the persistent, yet gentle flutter of change that evolves the educational landscape in almost imperceptible ways, but tumultuous paradigmatic gales that potentially change it beyond all recognition. Heralded by politicians, economists and capitalists, there is little doubt that the 1989 neoliberal tempest wrought havoc on notions of community and profession. The whirlwind shift from social democracy to market competition, managerialism and performativity saw critical voices silenced and educators disparagingly positioned as self-interested providers. In the rush to legislate Tomorrow’s Schools, 18,000 submissions remained unanalysed and therein lies a crucial lesson: we ignore research at our peril. As educators, we have a moral obligation to generate, disseminate and critique understandings of leadership, policy and practice; to remain open to counter perspectives; and to contribute positively and hopefully to research that empowers and emancipates. Consistent with JELPP’s commitment to honouring diversity in leadership focus, setting, and authorship, articles in this year’s general edition offer fresh insight into topics of interconnected and perennial importance: native knowledge, instructional leadership, indigenous teachers, appraisal, professional values, and safe schools.

text: Editorial As New Zealand contemplates wholesale review of the formal schooling system and the leadership implications thereof, the winds of educational change begin to swirl. Not the persistent, yet gentle flutter of change that evolves the educational landscape in almost imperceptible ways, but tumultuous paradigmatic gales that potentially change it beyond all recognition. Heralded by politicians, economists and capitalists, there is little doubt that the 1989 neoliberal tempest wrought havoc on notions of community and profession. The whirlwind shift from social democracy to market competition, managerialism and performativity saw critical voices silenced and educators disparagingly positioned as self-interested providers. In the rush to legislate Tomorrow’s Schools, 18,000 submissions remained unanalysed and therein lies a crucial lesson: we ignore research at our peril. As educators, we have a moral obligation to generate, disseminate and critique understandings of leadership, policy and practice; to remain open to counter perspectives; and to contribute positively and hopefully to research that empowers and emancipates. Consistent with JELPP’s commitment to honouring diversity in leadership focus, setting, and authorship, articles in this year’s general edition offer fresh insight into topics of interconnected and perennial importance: native knowledge, instructional leadership, indigenous teachers, appraisal, professional values, and safe schools.

year: 2019

title: Health literacy as a complex practice

authors: Hunter, Judy

abstract: As attention to health literacy grows as an area for policy intervention, policy discourse continues to draw on skills deficit and patient compliance, buttressed by the dominant political discourse of individual responsibility. But for patients, the health domain is interwoven with linguistic challenges, significant affective issues, underlying cultural dimensions, political and economic exigencies, variable access to resources, and cognitive and situated complexity. From these perspectives, this article reports on findings of an ongoing study of health literacy demands in the Midlands region of the North Island of New Zealand, an area of high ethnic and socio-economic diversity. The study focuses on patients with diabetes and cardiovascular disease - two chronic areas strongly associated with ‘failure to care’ and identifed as having reached epidemic proportions. It analyses work to date: health professionals’ conceptions of and responses to perceived patients’ health literacy needs, and health information documents for patients. Implications of the study support the need for improvement in language and literacy skills among patients, but also the recognition of complexity and a collective responsibility for effective health communication.

text: Health literacy as a complex practice As attention to health literacy grows as an area for policy intervention, policy discourse continues to draw on skills deficit and patient compliance, buttressed by the dominant political discourse of individual responsibility. But for patients, the health domain is interwoven with linguistic challenges, significant affective issues, underlying cultural dimensions, political and economic exigencies, variable access to resources, and cognitive and situated complexity. From these perspectives, this article reports on findings of an ongoing study of health literacy demands in the Midlands region of the North Island of New Zealand, an area of high ethnic and socio-economic diversity. The study focuses on patients with diabetes and cardiovascular disease - two chronic areas strongly associated with ‘failure to care’ and identifed as having reached epidemic proportions. It analyses work to date: health professionals’ conceptions of and responses to perceived patients’ health literacy needs, and health information documents for patients. Implications of the study support the need for improvement in language and literacy skills among patients, but also the recognition of complexity and a collective responsibility for effective health communication.

year: 2012