title: Lake Rotorua and Lake Rotoehu: Total and non-crystalline aluminium content in bottom sediments

authors: Tempero, Grant Wayne

abstract: The application of alum (aluminium sulphate) is widely used for lake restoration. Aluminium binds dissolved reactive phosphate (DRP) reducing its availability to phytoplankton and inhibiting algal blooms. The Bay of Plenty Regional Council has conducted continuous alum treatment of the Puarenga and Utuhina Streams discharging to Lake Rotorua and the Waitangi Soda Stream entering Lake Rotoehu for nearly 10 years. This has resulted in the addition of more than 722.3 tonnes of aluminium to Lake Rotorua and 80.8 tonnes to Lake Rotoehu. Dissolved reactive phosphorus levels within the streams have been markedly reduced due to alum dosing. This appears to support long-term trends of reducing Trophic Level Index (TLI) levels in both lakes, indicative of water quality improvement, with greater
success in Lake Rotorua. In addition, secondary sediment capping effects from the dosing have been suggested as a potential process explaining recent improvements in lake water quality. Accumulation of alum-derived aluminium in lake sediments potentially provides the additional benefit of adsorbing dissolved phosphorus which might otherwise be released from lake sediments under anoxic conditions.
The University of Waikato was contracted by the Bay of Plenty Regional Council to conduct on-going monitoring of sediment aluminium and phosphorus concentrations in lakes Rotorua and Rotoehu. In addition to sediment total aluminium content, the proportion of amorphous (non-crystalline) aluminium was also determined. Amorphous aluminium is recognised as the fraction of total aluminium able to adsorb dissolved phosphorus, sequestering it from the water column. For this study it was assumed that increased proportions of amorphous aluminium were derived from alum dosing.
Fifteen sediment cores were taken from Lake Rotorua and the findings from the analysis of these cores was compared to data collected in 2006 and 2012. Sites were chosen to represent three different depositional zones: zone 1 (Sites Ru1-4) to represent the immediate depositional area of the treated streams, zone 2 (Sites Ru5-11) to represent the main sediment accumulation basin (<20 m water depth) and zone 3 (Sites Ru12-15) to represent an area of low sediment accumulation (< 20 m water depth). Analysis of the sediment showed little or no accumulation of aluminium in either zone 2 or zone 3 compared to similar surveys conducted in 2006 and 2012. There was also no change in the mean sediment total aluminium content for zone 1, however, two zone 1 sites (Ru2 and Ru3) contained notably higher proportions of amorphous aluminium in their surface sediments. In association with these two sites, surface sediment pore water dissolved reactive phosphate (DRP) concentrations were reduced compared to other sampled sites. These findings suggest that alum-derived aluminium is only accumulating in an area close to the discharge points of the Utuhina and Puarenga Streams, although further survey work will be needed for confirmation. The lack of aluminium accumulation in the main lake basin indicates that secondary sediment capping effects are unlikely to be substantial, and recent improvements in the water quality of Lake3 Rotorua are driven by other factors, such as a positive feed-back loop between reductions in organic matter sedimentation and nutrient regeneration.
A total of seven sediment cores were taken from Lake Rotoehu in a transect line running from the mouth of the Waitangi Stream out into the main basin. Significant accumulation of alum derived aluminium (>25,000 mg kg⁻¹) was found in the sediment of Te Weta Bay, however, no observable accumulation of aluminium (i.e., <5000 mg kg⁻¹) was found in the main basin of Lake Rotoehu. Impedance of flow from the large biomass of Ceratophyllum demersum in Te Weta Bay is likely preventing alum flocs from reaching the main lake basin, negating any hoped for benefits of DRP sequestration through sediment capping. In addition, large diel shifts in pH between 6 and 9.5 caused by photosynthesis-respiration cycles of C. demersum are causing dissolution of the aluminium-phosphorus bound precipitate, reducing the performance of the alum dosing programme.
It is recommended that an additional sediment survey be conducted around Kawaha Point and the area north of Sulphur Bay in Lake Rotorua to determine if these areas are accumulating aluminium derived from alum flocculent. Given improved understanding of processes though which alum dosing improves lake water quality, alum dosing rates for Lake Rotorua should be reviewed with the aim of testing if lower alum dose rates can achieve the TLI target. The Waitangi Soda Stream alum treatment programme should be reviewed in order to assess whether a more effective strategy can be implemented in the presence of potentially confounding factors such as lake weed and high iron levels in stream inflows.

text: Lake Rotorua and Lake Rotoehu: Total and non-crystalline aluminium content in bottom sediments The application of alum (aluminium sulphate) is widely used for lake restoration. Aluminium binds dissolved reactive phosphate (DRP) reducing its availability to phytoplankton and inhibiting algal blooms. The Bay of Plenty Regional Council has conducted continuous alum treatment of the Puarenga and Utuhina Streams discharging to Lake Rotorua and the Waitangi Soda Stream entering Lake Rotoehu for nearly 10 years. This has resulted in the addition of more than 722.3 tonnes of aluminium to Lake Rotorua and 80.8 tonnes to Lake Rotoehu. Dissolved reactive phosphorus levels within the streams have been markedly reduced due to alum dosing. This appears to support long-term trends of reducing Trophic Level Index (TLI) levels in both lakes, indicative of water quality improvement, with greater
success in Lake Rotorua. In addition, secondary sediment capping effects from the dosing have been suggested as a potential process explaining recent improvements in lake water quality. Accumulation of alum-derived aluminium in lake sediments potentially provides the additional benefit of adsorbing dissolved phosphorus which might otherwise be released from lake sediments under anoxic conditions.
The University of Waikato was contracted by the Bay of Plenty Regional Council to conduct on-going monitoring of sediment aluminium and phosphorus concentrations in lakes Rotorua and Rotoehu. In addition to sediment total aluminium content, the proportion of amorphous (non-crystalline) aluminium was also determined. Amorphous aluminium is recognised as the fraction of total aluminium able to adsorb dissolved phosphorus, sequestering it from the water column. For this study it was assumed that increased proportions of amorphous aluminium were derived from alum dosing.
Fifteen sediment cores were taken from Lake Rotorua and the findings from the analysis of these cores was compared to data collected in 2006 and 2012. Sites were chosen to represent three different depositional zones: zone 1 (Sites Ru1-4) to represent the immediate depositional area of the treated streams, zone 2 (Sites Ru5-11) to represent the main sediment accumulation basin (<20 m water depth) and zone 3 (Sites Ru12-15) to represent an area of low sediment accumulation (< 20 m water depth). Analysis of the sediment showed little or no accumulation of aluminium in either zone 2 or zone 3 compared to similar surveys conducted in 2006 and 2012. There was also no change in the mean sediment total aluminium content for zone 1, however, two zone 1 sites (Ru2 and Ru3) contained notably higher proportions of amorphous aluminium in their surface sediments. In association with these two sites, surface sediment pore water dissolved reactive phosphate (DRP) concentrations were reduced compared to other sampled sites. These findings suggest that alum-derived aluminium is only accumulating in an area close to the discharge points of the Utuhina and Puarenga Streams, although further survey work will be needed for confirmation. The lack of aluminium accumulation in the main lake basin indicates that secondary sediment capping effects are unlikely to be substantial, and recent improvements in the water quality of Lake3 Rotorua are driven by other factors, such as a positive feed-back loop between reductions in organic matter sedimentation and nutrient regeneration.
A total of seven sediment cores were taken from Lake Rotoehu in a transect line running from the mouth of the Waitangi Stream out into the main basin. Significant accumulation of alum derived aluminium (>25,000 mg kg⁻¹) was found in the sediment of Te Weta Bay, however, no observable accumulation of aluminium (i.e., <5000 mg kg⁻¹) was found in the main basin of Lake Rotoehu. Impedance of flow from the large biomass of Ceratophyllum demersum in Te Weta Bay is likely preventing alum flocs from reaching the main lake basin, negating any hoped for benefits of DRP sequestration through sediment capping. In addition, large diel shifts in pH between 6 and 9.5 caused by photosynthesis-respiration cycles of C. demersum are causing dissolution of the aluminium-phosphorus bound precipitate, reducing the performance of the alum dosing programme.
It is recommended that an additional sediment survey be conducted around Kawaha Point and the area north of Sulphur Bay in Lake Rotorua to determine if these areas are accumulating aluminium derived from alum flocculent. Given improved understanding of processes though which alum dosing improves lake water quality, alum dosing rates for Lake Rotorua should be reviewed with the aim of testing if lower alum dose rates can achieve the TLI target. The Waitangi Soda Stream alum treatment programme should be reviewed in order to assess whether a more effective strategy can be implemented in the presence of potentially confounding factors such as lake weed and high iron levels in stream inflows.

year: 2016

title: Batch-Incremental Learning for Mining Data Streams

authors: Holmes, Geoffrey

subjects: computer science

abstract: The data stream model for data mining places harsh restrictions on a learning algorithm. First, a model must be induced incrementally. Second, processing time for instances must keep up with their speed of arrival. Third, a model may only use a constant amount of memory, and must be ready for prediction at any point in time. We attempt to overcome these restrictions by presenting a data stream classification algorithm where the data is split into a stream of disjoint batches. Single batches of data can be processed one after the other by any standard non-incremental learning algorithm. Our approach uses ensembles of decision trees. These tree ensembles are iteratively merged into a single interpretable model of constant maximal size. Using benchmark datasets the algorithm is evaluated for accuracy against state-of-the-art algorithms that make use of the entire dataset.

text: Batch-Incremental Learning for Mining Data Streams The data stream model for data mining places harsh restrictions on a learning algorithm. First, a model must be induced incrementally. Second, processing time for instances must keep up with their speed of arrival. Third, a model may only use a constant amount of memory, and must be ready for prediction at any point in time. We attempt to overcome these restrictions by presenting a data stream classification algorithm where the data is split into a stream of disjoint batches. Single batches of data can be processed one after the other by any standard non-incremental learning algorithm. Our approach uses ensembles of decision trees. These tree ensembles are iteratively merged into a single interpretable model of constant maximal size. Using benchmark datasets the algorithm is evaluated for accuracy against state-of-the-art algorithms that make use of the entire dataset.

year: 2004

title: Insecure, unpredictable, hoping to survive: Four cases of Māori people living precariously in Hamilton, Aotearoa New Zealand

authors: Uerata, Lynley Moana

subjects: Māori

abstract: A conceptualisation of precarity is introduced and adopted. A critique of contemporary conceptualisations of precarity is presented, drawing especially on Stuart Hall’s interpretation of articulation and Marx’s concept of relative surplus population. Much of the literature on precarity focusses on the neoliberal mode of contemporary capitalism originating in the late 1970s. However, there is limited literature which explores precarity as a way of life. A precarious way of life is characterised by interacting forms of precarity which embed insecurity, instability, and unpredictability in the everyday lives of real people. An account of the Māori experience of precarity since the pre-colonial era to the present-day is presented. Māori are the indigenous people of Aotearoa New Zealand who were colonised by the British Empire in the 1800s. 
The main research questions addressed in my thesis are: What forms of precarity are present in the everyday context? How do forms of precarity relate to each other? How do forms of precarity relate to being Māori? What kinds of support do those living with precarity gain from social structures, institutions, and social actors? What is the role of culture in the way Māori experience and mediate precarity? An analysis of semi-structured in-depth engagements with Māori people living precariously in Hamilton, Aotearoa New Zealand in 2016, based on four case studies, shows the character and significance of forms, sources, and effects of precarity in everyday life. As historical processes continue to overdetermine experiences of social structures and institutions in the present, in a contemporary capitalist context precarity arises from a wide range of interacting sources, forms, and effects of precarity. Among the different kinds of actors and organisations which comprise the support systems constructed to mediate precarity in the everyday context, cultural practices and resources can play a significant role for people who are culturally connected. When people are integrated into their local and cultural communities, they can cope better with a precarious way of life.

text: Insecure, unpredictable, hoping to survive: Four cases of Māori people living precariously in Hamilton, Aotearoa New Zealand A conceptualisation of precarity is introduced and adopted. A critique of contemporary conceptualisations of precarity is presented, drawing especially on Stuart Hall’s interpretation of articulation and Marx’s concept of relative surplus population. Much of the literature on precarity focusses on the neoliberal mode of contemporary capitalism originating in the late 1970s. However, there is limited literature which explores precarity as a way of life. A precarious way of life is characterised by interacting forms of precarity which embed insecurity, instability, and unpredictability in the everyday lives of real people. An account of the Māori experience of precarity since the pre-colonial era to the present-day is presented. Māori are the indigenous people of Aotearoa New Zealand who were colonised by the British Empire in the 1800s. 
The main research questions addressed in my thesis are: What forms of precarity are present in the everyday context? How do forms of precarity relate to each other? How do forms of precarity relate to being Māori? What kinds of support do those living with precarity gain from social structures, institutions, and social actors? What is the role of culture in the way Māori experience and mediate precarity? An analysis of semi-structured in-depth engagements with Māori people living precariously in Hamilton, Aotearoa New Zealand in 2016, based on four case studies, shows the character and significance of forms, sources, and effects of precarity in everyday life. As historical processes continue to overdetermine experiences of social structures and institutions in the present, in a contemporary capitalist context precarity arises from a wide range of interacting sources, forms, and effects of precarity. Among the different kinds of actors and organisations which comprise the support systems constructed to mediate precarity in the everyday context, cultural practices and resources can play a significant role for people who are culturally connected. When people are integrated into their local and cultural communities, they can cope better with a precarious way of life.

year: 2021