title: Ecological effects of artificial mixing in Lake Rotoehu

authors: McBride, Chris G.

abstract: Lake Rotoehu is a eutrophic, moderately large (795 ha), shallow (mean depth 8.2 m), polymictic lake in the Rotorua/Te Arawa lake district. Land use intensification, water level changes, and nutrient-rich geothermal inflows are some of the factors which may have contributed to severe cyanobacteria blooms over the past 20 years.
Bay of Plenty Regional Council (BoPRC) is charged with maintaining the ecosystem health of Lake Rotoehu. In 2007 BoPRC published the Lake Rotoehu Action Plan, outlining multiple restoration initiatives to reduce nutrient loading to the lake. Among these initiatives was a trial of artificial mixing to increase vertical circulation within the water column, preventing the formation of stratification. Two water column mixing devices were deployed on the lake bed of Lake Rotoehu from November 2012 to June 2014 (and are ongoing). These devices force compressed air through a diffuser near the bottom of the lake water column in the central lake basin. Buoyancy caused by the rising bubbles draws water from the bottom of the lake up through large vertical cylinders to the surface, where the entrained water is subsequently directed horizontally along the water surface. The University of Waikato was contracted to monitor the physical (temperature and dissolved oxygen), chemical (nutrients), and biological (phytoplankton and zooplankton) effects of the mixing devices on the lake. This work encompassed a range of instrumentation, laboratory analyses, and species enumeration from water samples.
In addition, an evaluation of the area of effect and strength of current generated by the mixing devices was conducted by the National Institute of Water and Atmospheric Research (NIWA), the results of which are reported here. Rhodamine dye tracer injected into the northern arm of the southern mixing device revealed that cooler hypolimnetic water was being brought to the surface. A component of the water entrained in this plume flowed away from the mixing device for at least 90 m. Parts of the plume also detrained from it, sinking towards the thermocline. Plumes from the mixing devices were tracked by Acoustic Doppler Current Meters (ADCM) or Profilers. The ADCM data revealed that the plume gradually dispersed laterally with increasing distance from the mixing device, and plume velocities were not elevated above background levels at c. 70 m from the mixing device. Although current velocities measured in the plume were generally low (<1 cm s⁻¹ to 25 cm s⁻¹; average 5.5 cm s⁻¹) they could be clearly distinguished from wind driven currents. 
Changes to the water column thermal profile were observed adjacent to the mixing devices, however, modification of the water column temperature structure across the lake (i.e., greater than a hundred metres from the devices) was not observed. Interpretations of the effect of the aeration devices was somewhat confounded by the period prior to installation of the machines (summer 2012) being cold and windy relative to weather conditions during the period of device deployment, which were unusually hot and dry (summer 2013 and 2014). These conditions resulted in Lake Rotoehu being stratified more often and strongly than in the summer prior to device installation. Additional factors affecting the aeration device operation are discussed in the report.
Analyses of nutrient concentrations, water clarity, and trophic status indicators have shown some improvement of Lake Rotoehu over recent years. However, the Trophic Level Index (TLI) has not yet met the target of 3.9 specified by the Rotoehu Action Plan. Water quality assessed by these indicators was comparatively good in 2012 - June 2014 despite the sustained periods of thermal stratification that contributed to significant oxygen depletion in bottom waters.
Localised effects of mixing included homogenisation of the cyanobacterial community through the water column and a decrease in the Bray-Curtis similarity index of the plankton community between mixing sites (i.e. near the aeration device) and controls (i.e. several hundred metres away from the mixing device). These results are consistent with physical observations of localised changes in thermal structure around the aeration devices. No significant changes occurred in plankton community composition at the whole-lake scale during aerator operation during the 2013 and 2014. By contrast, plankton community composition showed large seasonal and inter-annual variability including presence of invasive species.
Results suggest that the mixing devices installed in Lake Rotoehu are able to draw hypolimnetic water to the surface. The resulting horizontal plume rapidly becomes mixed with surface waters over distances of 50-60 m from the aerator but can also be tracked as it plunges towards the thermocline at these distances. Some localised effects were detected near the aerators but there were no detectable lake-scale effects. By contrast, there have been progressive improvements in water quality at a whole-lake scale over recent years and these may relate to alum dosing of the major geothermal inflow to the lake, weed harvesting and initial decreases in external nutrient inputs in response to changes in land use and land-use practices. Further monitoring will help clarify these observations, and an additional year of mixing device deployment aims to improve operational efficiency of the devices and quantify effects of proposed increases in air flow rates.

text: Ecological effects of artificial mixing in Lake Rotoehu Lake Rotoehu is a eutrophic, moderately large (795 ha), shallow (mean depth 8.2 m), polymictic lake in the Rotorua/Te Arawa lake district. Land use intensification, water level changes, and nutrient-rich geothermal inflows are some of the factors which may have contributed to severe cyanobacteria blooms over the past 20 years.
Bay of Plenty Regional Council (BoPRC) is charged with maintaining the ecosystem health of Lake Rotoehu. In 2007 BoPRC published the Lake Rotoehu Action Plan, outlining multiple restoration initiatives to reduce nutrient loading to the lake. Among these initiatives was a trial of artificial mixing to increase vertical circulation within the water column, preventing the formation of stratification. Two water column mixing devices were deployed on the lake bed of Lake Rotoehu from November 2012 to June 2014 (and are ongoing). These devices force compressed air through a diffuser near the bottom of the lake water column in the central lake basin. Buoyancy caused by the rising bubbles draws water from the bottom of the lake up through large vertical cylinders to the surface, where the entrained water is subsequently directed horizontally along the water surface. The University of Waikato was contracted to monitor the physical (temperature and dissolved oxygen), chemical (nutrients), and biological (phytoplankton and zooplankton) effects of the mixing devices on the lake. This work encompassed a range of instrumentation, laboratory analyses, and species enumeration from water samples.
In addition, an evaluation of the area of effect and strength of current generated by the mixing devices was conducted by the National Institute of Water and Atmospheric Research (NIWA), the results of which are reported here. Rhodamine dye tracer injected into the northern arm of the southern mixing device revealed that cooler hypolimnetic water was being brought to the surface. A component of the water entrained in this plume flowed away from the mixing device for at least 90 m. Parts of the plume also detrained from it, sinking towards the thermocline. Plumes from the mixing devices were tracked by Acoustic Doppler Current Meters (ADCM) or Profilers. The ADCM data revealed that the plume gradually dispersed laterally with increasing distance from the mixing device, and plume velocities were not elevated above background levels at c. 70 m from the mixing device. Although current velocities measured in the plume were generally low (<1 cm s⁻¹ to 25 cm s⁻¹; average 5.5 cm s⁻¹) they could be clearly distinguished from wind driven currents. 
Changes to the water column thermal profile were observed adjacent to the mixing devices, however, modification of the water column temperature structure across the lake (i.e., greater than a hundred metres from the devices) was not observed. Interpretations of the effect of the aeration devices was somewhat confounded by the period prior to installation of the machines (summer 2012) being cold and windy relative to weather conditions during the period of device deployment, which were unusually hot and dry (summer 2013 and 2014). These conditions resulted in Lake Rotoehu being stratified more often and strongly than in the summer prior to device installation. Additional factors affecting the aeration device operation are discussed in the report.
Analyses of nutrient concentrations, water clarity, and trophic status indicators have shown some improvement of Lake Rotoehu over recent years. However, the Trophic Level Index (TLI) has not yet met the target of 3.9 specified by the Rotoehu Action Plan. Water quality assessed by these indicators was comparatively good in 2012 - June 2014 despite the sustained periods of thermal stratification that contributed to significant oxygen depletion in bottom waters.
Localised effects of mixing included homogenisation of the cyanobacterial community through the water column and a decrease in the Bray-Curtis similarity index of the plankton community between mixing sites (i.e. near the aeration device) and controls (i.e. several hundred metres away from the mixing device). These results are consistent with physical observations of localised changes in thermal structure around the aeration devices. No significant changes occurred in plankton community composition at the whole-lake scale during aerator operation during the 2013 and 2014. By contrast, plankton community composition showed large seasonal and inter-annual variability including presence of invasive species.
Results suggest that the mixing devices installed in Lake Rotoehu are able to draw hypolimnetic water to the surface. The resulting horizontal plume rapidly becomes mixed with surface waters over distances of 50-60 m from the aerator but can also be tracked as it plunges towards the thermocline at these distances. Some localised effects were detected near the aerators but there were no detectable lake-scale effects. By contrast, there have been progressive improvements in water quality at a whole-lake scale over recent years and these may relate to alum dosing of the major geothermal inflow to the lake, weed harvesting and initial decreases in external nutrient inputs in response to changes in land use and land-use practices. Further monitoring will help clarify these observations, and an additional year of mixing device deployment aims to improve operational efficiency of the devices and quantify effects of proposed increases in air flow rates.

year: 2015

title: Exploring different 'perspectives' in secondary geography: Professional development options

authors: Chalmers, Lex

subjects: education policy

abstract: Significant changes have occurred in the worlds of geography since 1973, and a substantial literature has emerged about these changes and their effects on the 'divide' between secondary and tertiary geographers. We suggest that while the divide has not had much effect on the content taught in secondary geography in New Zealand and Britain, exposure to a range of perspectives on this content is a neglected area of professional development. Post-Fordism and deep ecology are described as perspectives that are not widely used in delivering secondary geography content. We argue firstly that effective use of different perspectives needs to be based on professional, personal and social change, and secondly that the Internet is a powerful tool in the engineering of such change.

text: Exploring different 'perspectives' in secondary geography: Professional development options Significant changes have occurred in the worlds of geography since 1973, and a substantial literature has emerged about these changes and their effects on the 'divide' between secondary and tertiary geographers. We suggest that while the divide has not had much effect on the content taught in secondary geography in New Zealand and Britain, exposure to a range of perspectives on this content is a neglected area of professional development. Post-Fordism and deep ecology are described as perspectives that are not widely used in delivering secondary geography content. We argue firstly that effective use of different perspectives needs to be based on professional, personal and social change, and secondly that the Internet is a powerful tool in the engineering of such change.

year: 2002

title: Pilot study investigating pathway for practitioner engagement with whānau during a self-control activity: Implications for uptake in the home and for empowered engagement.

authors: Watson, Kaitlyn

subjects: Community psychology

abstract: There is a gap in youth mentoring services using the home environment of at-risk youth to encourage development of the skills worked on within mentoring. This thesis explores whether a game-based intervention situated in the home environment of youth may initiate changes in behaviour that coincide with their learning during mentoring. Participants were recruited through a private youth mentoring service within Whāngarei. Participants included whānau of youth who are enrolled in the Awhi Ako youth mentoring service and their respective mentors. The Awhi Ako mentoring service aims to support youth through their selected needs by a wider wraparound service.
A game was picked to introduce to whānau to play together at home. This game contained a mechanism that may reward self-control behaviours. Whānau were interviewed and asked to discuss their child’s self-control behaviours before the introduction of the game and any changes after playing the game. 
A principal focus of this thesis is on practitioner engagement with the whānau of mentored youth. Practitioner engagement with communities and people is an integral value underpinning Community psychology. Whānau within the youth mentoring service include Māori, Pasifika, Pākehā and mixed ethnic backgrounds. A core focus of this thesis is understanding the relationship between practitioner and participants and how this impacts upon uptake of the introduction of the activity. In accordance with community psychology underpinnings and values of cultural awareness, cultural respect and understanding this thesis aspires to provide evidence towards the importance of this relationship. Another key focus of this thesis is comprehending the multifaceted effects of an intervention within the home environment and how this impacts mentors, the home environment and the development of youth. Emphasizing a fundamental principle of community psychology of interconnectedness between all facets of a persons life. 
The conclusions drawn from this thesis illustrate the importance of developing a relationship with whānau a key focus to their willingness to participate and actively engage in this pilot study. The findings from this pilot study indicate that whānau experienced hardship and that whānau within at-risk environments had competing priorities that impeded the introduction of home-based activities.

text: Pilot study investigating pathway for practitioner engagement with whānau during a self-control activity: Implications for uptake in the home and for empowered engagement. There is a gap in youth mentoring services using the home environment of at-risk youth to encourage development of the skills worked on within mentoring. This thesis explores whether a game-based intervention situated in the home environment of youth may initiate changes in behaviour that coincide with their learning during mentoring. Participants were recruited through a private youth mentoring service within Whāngarei. Participants included whānau of youth who are enrolled in the Awhi Ako youth mentoring service and their respective mentors. The Awhi Ako mentoring service aims to support youth through their selected needs by a wider wraparound service.
A game was picked to introduce to whānau to play together at home. This game contained a mechanism that may reward self-control behaviours. Whānau were interviewed and asked to discuss their child’s self-control behaviours before the introduction of the game and any changes after playing the game. 
A principal focus of this thesis is on practitioner engagement with the whānau of mentored youth. Practitioner engagement with communities and people is an integral value underpinning Community psychology. Whānau within the youth mentoring service include Māori, Pasifika, Pākehā and mixed ethnic backgrounds. A core focus of this thesis is understanding the relationship between practitioner and participants and how this impacts upon uptake of the introduction of the activity. In accordance with community psychology underpinnings and values of cultural awareness, cultural respect and understanding this thesis aspires to provide evidence towards the importance of this relationship. Another key focus of this thesis is comprehending the multifaceted effects of an intervention within the home environment and how this impacts mentors, the home environment and the development of youth. Emphasizing a fundamental principle of community psychology of interconnectedness between all facets of a persons life. 
The conclusions drawn from this thesis illustrate the importance of developing a relationship with whānau a key focus to their willingness to participate and actively engage in this pilot study. The findings from this pilot study indicate that whānau experienced hardship and that whānau within at-risk environments had competing priorities that impeded the introduction of home-based activities.

year: 2024