title: High Frequency Monitoring and Three-Dimensional Modelling of Temporal Variations in Water Quality of Lake Rotorua, New Zealand

authors: Zhang, Chenguang

subjects: Lake Rotorua

abstract: Over the last few decades, anthropogenic eutrophication has become a significant problem in New Zealand and other parts of the world. Lake Rotorua is located in the central North Island, New Zealand. It is a lake with significant historical, cultural and recreational values that has undergone anthropogenic eutrophication.

Lake Rotorua has been exposed to anthropogenic impacts through conversion of forested land to agricultural use within its catchment, and the discharge of domestic sewage into the lake. Cyanobacterial blooms have become a common occurrence in the lake each summer. These blooms not only reduce aesthetic appeal but also have potential to affect human health. Lake stratification and physical mixing events are the most important factors influencing nutrient availability and phytoplankton growth in Lake Rotorua.

The main objective of this study was to use high frequency monitoring data to investigate the significance of lake stratification events and how these events interact with the development of the cyanobacteria population and changes in nutrient concentrations in Lake Rotorua. The second objective was to use an ecological model to understand the relationship between physical, chemical and biological variables, and phytoplankton dynamics.

Data from a high frequency real-time water quality monitoring buoy was used as the basis for 12 sampling trips to Lake Rotorua timed around stratification and mixing events. Water samples were collected from five different sites for nutrient analysis, chlorophyll a analysis, and phytoplankton and zooplankton identification at depth intervals of 6 meters. Profiles were taken for temperature, dissolved oxygen and fluorescence. Total suspended solids and volatile suspended solids were also analysed. The data provided by the buoy, combined with additional sampling and measurements around stratification events, were used to calibrate a three-dimensional ecosystem model, ELCOM-CAEDYM.

Periods consisting of a few days of high solar radiation and low winds caused Lake Rotorua to become stratified between 26 January 2009 and 20 February 2009. During this stratification period the bottom waters became deoxygenated and there were large increases in of phosphorus and nitrogen concentrations in bottom waters, which were subsequently dispersed through the water column when the lake mixed again. Ammonium and phosphate were the dominant species of inorganic nitrogen and phosphorus in bottom waters during the periods of stratification. Upon mixing there was rapid growth of cyanobacteria (Microcystis sp. and Anabaena sp.). For the zooplankton community, copepod and rotifer densities increased significantly after the stratification event and replaced the previously dominant cladocerans.

In the study high frequency modelling with ELCOM-CADYM simulated the general trends of water temperature, dissolved oxygen and nutrient concentrations in Lake Rotorua. The model captured the water temperature fluctuation before, during, and after lake stratification as well as subsequent dissolved oxygen changes over time and space. Simulated nutrient concentrations were close to the field measurements, in particular NH4, TN and TP. Some issues occurred with high frequency simulations such as being unable to capture the strong fluctuations of lake surface temperature, and the magnitude of the decreases in dissolved oxygen under strong stratification.

text: High Frequency Monitoring and Three-Dimensional Modelling of Temporal Variations in Water Quality of Lake Rotorua, New Zealand Over the last few decades, anthropogenic eutrophication has become a significant problem in New Zealand and other parts of the world. Lake Rotorua is located in the central North Island, New Zealand. It is a lake with significant historical, cultural and recreational values that has undergone anthropogenic eutrophication.

Lake Rotorua has been exposed to anthropogenic impacts through conversion of forested land to agricultural use within its catchment, and the discharge of domestic sewage into the lake. Cyanobacterial blooms have become a common occurrence in the lake each summer. These blooms not only reduce aesthetic appeal but also have potential to affect human health. Lake stratification and physical mixing events are the most important factors influencing nutrient availability and phytoplankton growth in Lake Rotorua.

The main objective of this study was to use high frequency monitoring data to investigate the significance of lake stratification events and how these events interact with the development of the cyanobacteria population and changes in nutrient concentrations in Lake Rotorua. The second objective was to use an ecological model to understand the relationship between physical, chemical and biological variables, and phytoplankton dynamics.

Data from a high frequency real-time water quality monitoring buoy was used as the basis for 12 sampling trips to Lake Rotorua timed around stratification and mixing events. Water samples were collected from five different sites for nutrient analysis, chlorophyll a analysis, and phytoplankton and zooplankton identification at depth intervals of 6 meters. Profiles were taken for temperature, dissolved oxygen and fluorescence. Total suspended solids and volatile suspended solids were also analysed. The data provided by the buoy, combined with additional sampling and measurements around stratification events, were used to calibrate a three-dimensional ecosystem model, ELCOM-CAEDYM.

Periods consisting of a few days of high solar radiation and low winds caused Lake Rotorua to become stratified between 26 January 2009 and 20 February 2009. During this stratification period the bottom waters became deoxygenated and there were large increases in of phosphorus and nitrogen concentrations in bottom waters, which were subsequently dispersed through the water column when the lake mixed again. Ammonium and phosphate were the dominant species of inorganic nitrogen and phosphorus in bottom waters during the periods of stratification. Upon mixing there was rapid growth of cyanobacteria (Microcystis sp. and Anabaena sp.). For the zooplankton community, copepod and rotifer densities increased significantly after the stratification event and replaced the previously dominant cladocerans.

In the study high frequency modelling with ELCOM-CADYM simulated the general trends of water temperature, dissolved oxygen and nutrient concentrations in Lake Rotorua. The model captured the water temperature fluctuation before, during, and after lake stratification as well as subsequent dissolved oxygen changes over time and space. Simulated nutrient concentrations were close to the field measurements, in particular NH4, TN and TP. Some issues occurred with high frequency simulations such as being unable to capture the strong fluctuations of lake surface temperature, and the magnitude of the decreases in dissolved oxygen under strong stratification.

year: 2010

title: How to read the Qur’an [Book review]

authors: Pratt, Douglas

subjects: book review

abstract: This article reviews the book: “How to Read the Qur’an”, by Mona Siddiqui.

text: How to read the Qur’an [Book review] This article reviews the book: “How to Read the Qur’an”, by Mona Siddiqui.

year: 2009

title: Protecting Māori data: Can a Privacy Code of Practice provide a partial solution?

authors: Watts, David

abstract: This paper explores whether a Māori Data Privacy Code, developed under the Privacy Act 2020, could provide additional protection for classes of information that are regarded by Māori as tapu. The Act already covers the personal information of Māori individuals in the same way it does any other individual. We argue that a MDP Code could offer additional protection for particular classes of sensitive personal information – specifically whakapapa data and data pertaining to deceased Māori. A MDP Code could restrict the purposes for which such information can be collected, used, disclosed, retained, stored and disposed of; put stronger requirements on agencies to demonstrate that their collection and use of this information is justified; require free, prior and informed consent for its use and disclosure; and provide for greater transparency and independent Māori oversight.

text: Protecting Māori data: Can a Privacy Code of Practice provide a partial solution? This paper explores whether a Māori Data Privacy Code, developed under the Privacy Act 2020, could provide additional protection for classes of information that are regarded by Māori as tapu. The Act already covers the personal information of Māori individuals in the same way it does any other individual. We argue that a MDP Code could offer additional protection for particular classes of sensitive personal information – specifically whakapapa data and data pertaining to deceased Māori. A MDP Code could restrict the purposes for which such information can be collected, used, disclosed, retained, stored and disposed of; put stronger requirements on agencies to demonstrate that their collection and use of this information is justified; require free, prior and informed consent for its use and disclosure; and provide for greater transparency and independent Māori oversight.

year: 2025-10