title: The influence of entrance constriction on hydrodynamics and intertidal morphology within estuarine basins

authors: de Ruiter, Peter Jaap

subjects: estuaries

abstract: We investigate the influence of basin entrance constriction on current velocities, tidal asymmetry, bed shear stresses and intertidal morphology by using a numerical model developed in Delft3D. Hypsometric curves created for six sub-estuaries within Tauranga Harbour indicate a possible link between intertidal hypsometry and entrance constriction. Model results for both spring- and neap tidal cycles show that a constricted subestuary with a deep entrance channel is associated with low current velocities and bed shear stresses in the centre of the basin– conditions favourable for sediment deposition. These constricted geometries are shown to be characterized by convex intertidal equilibrium profiles. Unconstricted sub-estuary model results display an even distribution of relatively high current velocities and bed shear stresses resulting in potential for erosion throughout the estuary. The unconstricted basins in our study are mainly associated with concave intertidal equilibrium profiles. Flood dominance increases from the entrance further into the estuary for both constricted and unconstricted conditions.

text: The influence of entrance constriction on hydrodynamics and intertidal morphology within estuarine basins We investigate the influence of basin entrance constriction on current velocities, tidal asymmetry, bed shear stresses and intertidal morphology by using a numerical model developed in Delft3D. Hypsometric curves created for six sub-estuaries within Tauranga Harbour indicate a possible link between intertidal hypsometry and entrance constriction. Model results for both spring- and neap tidal cycles show that a constricted subestuary with a deep entrance channel is associated with low current velocities and bed shear stresses in the centre of the basin– conditions favourable for sediment deposition. These constricted geometries are shown to be characterized by convex intertidal equilibrium profiles. Unconstricted sub-estuary model results display an even distribution of relatively high current velocities and bed shear stresses resulting in potential for erosion throughout the estuary. The unconstricted basins in our study are mainly associated with concave intertidal equilibrium profiles. Flood dominance increases from the entrance further into the estuary for both constricted and unconstricted conditions.

year: 2017

title: Online collaborative learning in tertiary ICT education to enhance students' learning in Malaysia

authors: Mohamad Said, Mohd Nihra Haruzuan Bin

subjects: Online learning environments

abstract: This study investigated the nature of students’, and student group, interactions through the incorporation of an online collaborative learning (OCL) initiative, with its aim to enhance students’ learning in a Malaysian tertiary classroom. In order to contribute to knowledge and understanding about the nature and quality of OCL, the learning processes and outcomes were drawn predominantly from Harasim’s model, with inclusion of a socio-cultural framework aimed at enhancing learning outcomes for undergraduate science and ICT education students. Harasim’s model of OCL that was used in the intervention includes steps to setting up the stage and a system for Idea Generating (IG), modeling and guiding the OCL discussions for Idea Organizing (IO), and evaluating and reflecting the OCL discussions for Intellectual Convergence (IC). The interactions in OCL were analysed through four dimensions: participative, interactive, social, and cognitive in support of the students’ cognitive, social and emotional development.
The OCL intervention in this study was conducted through an ICT education course in a Malaysian university that required OCL discussions for 13 weeks: the first four weeks were intra-group work discussions (Task 1), followed by four/five weeks of inter-group work discussions (Task 2), and the remaining four weeks were for the final intra-group work discussions (Task 3). The OCL intervention was aimed at facilitating interdisciplinary collaboration and interaction between students from Chemistry, Physics and Mathematics majors through the university’s Learning Management System (Moodle), which provided the shared space for the OCL discourse and tools for collaboration. A total of nine groups of four to six students (N=46) were involved in this study. In order to evaluate the OCL intervention using a holistic view, an interpretive approach that included the collection of quantitative and qualitative data was adopted to frame the collection and analysis of the data. Quantitative data were obtained from online questionnaires, together with online data based on the frequency of students’ posts in participative, interactive, social, and cognitive dimensions. Qualitative data were gathered via interviews with students (group and post-course interviews) and lecturers, and online transcripts that included online postings and students’ online journal entries. These data were collected and analysed in order to triangulate the findings and to help the researcher assess the extent to which the intervention was successful in enhancing students’ learning.
The findings from the study revealed the nature of students’ interactions in OCL correspond with particular socio-cultural views that students’ interactions are characterised based on the participative, interactive, social and cognitive dimensions in support of the students’ cognitive, social and emotional development. From a socio-cultural perspective, the outcomes that arose from the study included:
•	The socio-cultural learning constructs have been useful as a framework for the analysis of the OCL intervention based on the participative, interactive, social and cognitive dimensions.
•	The affordances of the OCL group work helped the students’ in their group work.
•	The constraints of OCL influence the communication methods, and interaction styles used by students in achieving task goals through group work in the OCL intervention.
The findings also show students’ interactions and student group interactions were an important part of the learning process. The implementation of OCL intervention into the course can lead to the facilitation of the student group learning process as well as supporting their cognitive, social and emotional development, and potential constraints from the technology (e.g. Internet connection) or the lack of social and verbal cues (e.g. facial expression) can lead to different working methods of communication for achieving task goals and different styles of interactions. Overall, the findings of the study indicate the value of OCL in a tertiary classroom to enhance learning.

text: Online collaborative learning in tertiary ICT education to enhance students' learning in Malaysia This study investigated the nature of students’, and student group, interactions through the incorporation of an online collaborative learning (OCL) initiative, with its aim to enhance students’ learning in a Malaysian tertiary classroom. In order to contribute to knowledge and understanding about the nature and quality of OCL, the learning processes and outcomes were drawn predominantly from Harasim’s model, with inclusion of a socio-cultural framework aimed at enhancing learning outcomes for undergraduate science and ICT education students. Harasim’s model of OCL that was used in the intervention includes steps to setting up the stage and a system for Idea Generating (IG), modeling and guiding the OCL discussions for Idea Organizing (IO), and evaluating and reflecting the OCL discussions for Intellectual Convergence (IC). The interactions in OCL were analysed through four dimensions: participative, interactive, social, and cognitive in support of the students’ cognitive, social and emotional development.
The OCL intervention in this study was conducted through an ICT education course in a Malaysian university that required OCL discussions for 13 weeks: the first four weeks were intra-group work discussions (Task 1), followed by four/five weeks of inter-group work discussions (Task 2), and the remaining four weeks were for the final intra-group work discussions (Task 3). The OCL intervention was aimed at facilitating interdisciplinary collaboration and interaction between students from Chemistry, Physics and Mathematics majors through the university’s Learning Management System (Moodle), which provided the shared space for the OCL discourse and tools for collaboration. A total of nine groups of four to six students (N=46) were involved in this study. In order to evaluate the OCL intervention using a holistic view, an interpretive approach that included the collection of quantitative and qualitative data was adopted to frame the collection and analysis of the data. Quantitative data were obtained from online questionnaires, together with online data based on the frequency of students’ posts in participative, interactive, social, and cognitive dimensions. Qualitative data were gathered via interviews with students (group and post-course interviews) and lecturers, and online transcripts that included online postings and students’ online journal entries. These data were collected and analysed in order to triangulate the findings and to help the researcher assess the extent to which the intervention was successful in enhancing students’ learning.
The findings from the study revealed the nature of students’ interactions in OCL correspond with particular socio-cultural views that students’ interactions are characterised based on the participative, interactive, social and cognitive dimensions in support of the students’ cognitive, social and emotional development. From a socio-cultural perspective, the outcomes that arose from the study included:
•	The socio-cultural learning constructs have been useful as a framework for the analysis of the OCL intervention based on the participative, interactive, social and cognitive dimensions.
•	The affordances of the OCL group work helped the students’ in their group work.
•	The constraints of OCL influence the communication methods, and interaction styles used by students in achieving task goals through group work in the OCL intervention.
The findings also show students’ interactions and student group interactions were an important part of the learning process. The implementation of OCL intervention into the course can lead to the facilitation of the student group learning process as well as supporting their cognitive, social and emotional development, and potential constraints from the technology (e.g. Internet connection) or the lack of social and verbal cues (e.g. facial expression) can lead to different working methods of communication for achieving task goals and different styles of interactions. Overall, the findings of the study indicate the value of OCL in a tertiary classroom to enhance learning.

year: 2013

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