title: Zooplankton Communities, and TLI and Lake Health Assessments, of Selected Lakes in the Wellington region

authors: Duggan, Ian C.

subjects: Lake Health Assessments

abstract: Zooplankton were collected from ten lakes in the Wellington Region in 2022, with a further three historic samples collected from 2019 (including one unique lake). These were used to explore community composition of these lakes, as well as trends in rotifer inferred TLI assessments, the proportions of native versus non-native zooplankton, and crustaceans versus rotifers. Based on these results, lakes can be ranked in the following order, from lowest to highest rotifer inferred TLI values; Lake Ngarara (1.8; oligotrophic), Lake Waitawa (3.9), Barton’s Lagoon (3.9; both mesotrophic), Turner’s Lagoon (4.0), Boggy Pond, (4.2), Waimanu Lagoon (4.5; all eutrophic), Lake Pounui (5.0), Lake Kohangatera (5.1), Matthew’s Lagoon (5.3; all supertrophic), Lake Waiorongomai (8.0) and Lake Nganoke (8.3; both hypertrophic). The Matthew’s Lagoon (both 5.3) and Lake Waitawa results (3.3 and 4.5) were averages of samples from two years. Nevertheless, these results should be treated with caution, due to being calculated from single samples, or samples from different years, rather than the recommended multiple samples collected over different seasons. Most of the lakes were devoid of non-native species. Nevertheless, Lakes Pounui and Waitawa both had populations of the introduced Daphnia galeata, which is native to northern hemisphere temperate regions (i.e., Holarctic), while Lake Waitawa also possessed a population of the Australian copepod Boeckella minuta. The latter record is interesting in that it is otherwise only known from constructed waters in New Zealand, including the Karori Reservoirs and Waikato Hydroelectricity Lakes. As such, this is the first record of this species established in a natural lake in New Zealand. The zooplankton community of Lake Pounui (98.7%), Lake Waitawa in 2019 (89.9%), Lake Waitawa in 2022 (76.7%) and Boggy Pond (73.1%) were heavily crustacean dominated, while Lake Kohangatera (5.9% crustaceans), Matthews Lagoon (23.5%), Lake Ngarara (27.9%), Lake Waiorongomai (28.6%), Barton’s Lagoon (30.5%), Lake Nganoke (32.6%) and Turner’s Lagoon (34.7%) were heavily rotifer dominated. Matthew’s Lagoon (52.1%) and Waimanu Lagoon (40.4%) had similar proportions of crustacean and rotifer zooplankton. The size distributions of zooplankton in Lakes Pounui and Waitawa are likely influenced by the crustacean invaders in these lakes. Different degrees of top-down control by zooplanktivorous fish, removing larger crustacean zooplankton, may influence the variability among the remaining waterbodies, though longer-term data and knowledge of fish communities is required to better determine this. Besides B. minuta, the waterbodies sampled included some unusual species. A Brachionus rotifer, with affinities to B. caudatus, was recoded from Lake Kohangatera and Boggy Pond; this seemingly represents an undescribed species. The typically estuarine copepod Gladioferens pectinatus and saline rotifer Brachionus plicatilis were recorded in Waimanu Lagoon, reflecting a probable marine influence in this lagoon. Gladioferens pectinatus was also recorded in Matthews Lagoon, representing a rare occurrence for this species in a freshwater lake.

text: Zooplankton Communities, and TLI and Lake Health Assessments, of Selected Lakes in the Wellington region Zooplankton were collected from ten lakes in the Wellington Region in 2022, with a further three historic samples collected from 2019 (including one unique lake). These were used to explore community composition of these lakes, as well as trends in rotifer inferred TLI assessments, the proportions of native versus non-native zooplankton, and crustaceans versus rotifers. Based on these results, lakes can be ranked in the following order, from lowest to highest rotifer inferred TLI values; Lake Ngarara (1.8; oligotrophic), Lake Waitawa (3.9), Barton’s Lagoon (3.9; both mesotrophic), Turner’s Lagoon (4.0), Boggy Pond, (4.2), Waimanu Lagoon (4.5; all eutrophic), Lake Pounui (5.0), Lake Kohangatera (5.1), Matthew’s Lagoon (5.3; all supertrophic), Lake Waiorongomai (8.0) and Lake Nganoke (8.3; both hypertrophic). The Matthew’s Lagoon (both 5.3) and Lake Waitawa results (3.3 and 4.5) were averages of samples from two years. Nevertheless, these results should be treated with caution, due to being calculated from single samples, or samples from different years, rather than the recommended multiple samples collected over different seasons. Most of the lakes were devoid of non-native species. Nevertheless, Lakes Pounui and Waitawa both had populations of the introduced Daphnia galeata, which is native to northern hemisphere temperate regions (i.e., Holarctic), while Lake Waitawa also possessed a population of the Australian copepod Boeckella minuta. The latter record is interesting in that it is otherwise only known from constructed waters in New Zealand, including the Karori Reservoirs and Waikato Hydroelectricity Lakes. As such, this is the first record of this species established in a natural lake in New Zealand. The zooplankton community of Lake Pounui (98.7%), Lake Waitawa in 2019 (89.9%), Lake Waitawa in 2022 (76.7%) and Boggy Pond (73.1%) were heavily crustacean dominated, while Lake Kohangatera (5.9% crustaceans), Matthews Lagoon (23.5%), Lake Ngarara (27.9%), Lake Waiorongomai (28.6%), Barton’s Lagoon (30.5%), Lake Nganoke (32.6%) and Turner’s Lagoon (34.7%) were heavily rotifer dominated. Matthew’s Lagoon (52.1%) and Waimanu Lagoon (40.4%) had similar proportions of crustacean and rotifer zooplankton. The size distributions of zooplankton in Lakes Pounui and Waitawa are likely influenced by the crustacean invaders in these lakes. Different degrees of top-down control by zooplanktivorous fish, removing larger crustacean zooplankton, may influence the variability among the remaining waterbodies, though longer-term data and knowledge of fish communities is required to better determine this. Besides B. minuta, the waterbodies sampled included some unusual species. A Brachionus rotifer, with affinities to B. caudatus, was recoded from Lake Kohangatera and Boggy Pond; this seemingly represents an undescribed species. The typically estuarine copepod Gladioferens pectinatus and saline rotifer Brachionus plicatilis were recorded in Waimanu Lagoon, reflecting a probable marine influence in this lagoon. Gladioferens pectinatus was also recorded in Matthews Lagoon, representing a rare occurrence for this species in a freshwater lake.

year: 2022

title: Toxicological effects of aluminium in relation to diel pH changes on fish and kōura

authors: Fensham, Emily

abstract: Since 2006, alum (aluminium sulphate; Al₂(SO₄)₃) has been applied to the Utuhina and Puarenga Streams at a targeted dose rate of 1 mg Al L⁻¹ to control phosphorus loading to Lake Rotorua. Alum dosing is widely used for water quality restoration and, under circumneutral pH (6-8), is considered to have no significant toxicological impacts at low to moderate (0.1–2 mg Al L⁻¹) concentrations. At circumneutral pH, alum forms aluminium hydroxide (AlOH₃), a white insoluble precipitate which adsorbs phosphorus, reducing its availability for phytoplankton growth. However, at high or low pH, monomeric and hydroxy aluminium species occur in varying proportions with respect to acidic (i.e., Al³⁺, AlOH²⁺, Al(OH)²⁺) and alkaline (i.e., Al(OH)₄⁻) conditions with increasing toxicity to aquatic organisms. 
Under typical conditions, the pH of Lake Rotorua is near pH 7, but due to its limited buffering capacity may reach pH 10 during intensive algal blooms. These diel increases in pH occur due to the photosynthetic uptake of CO₂ during the day, thereby increasing the environmental hydroxide concentration and raising the pH of the lake. At night, respiration releases CO₂, driving down the pH due to the formation of carbonic acid. Diel pH cycling has the potential to solubilise alum-derived aluminium, resulting in toxicological impacts on aquatic biota. Previous research has primarily focused on the toxicological impacts of aluminium under acidic or, more recently, alkaline conditions, however, potential impacts during transient exposure to alkaline pH have not been reported. 
The University of Waikato was contracted to investigate the effects of aluminium at 2 mg L⁻¹ in association with diel pH cycling on rainbow trout (Oncorhynchus mykiss), common bully (Gobiomorphus cotidianus) and kōura (Paranephrops planifrons) osmoregulation and respiration. Potential osmoregulatory effects were investigated by exposure of rainbow trout and kōura to aluminium at 2 mg L⁻¹ under diel pH cycling (pH 7–10) over 10 days. No significant differences between control and treatment groups were observed in either plasma and haemolymph osmolarity, haematocrit or haemoglobin concentration (Student’s t-test, P >0.05). A significant difference (Student’s t-test, P <0.05) in the mean cell haemoglobin concentration (MCHC) in the rainbow trout control group was attributed to erythrocyte swelling, suggesting a generalised stress-induced response rather than an impact from aluminium. Histological examination of kōura and rainbow trout gill tissue was also conducted, with abnormalities observed within both control and treatment groups for each species. A significant difference (Kolomogorov-Smirnov, P <0.05) was observed between kōura control and treatment groups, indicating that kōura gills may be more susceptible to erosional damage from precipitated aluminium hydroxide. It was concluded that diel pH cycling and exposure to 2 mg Al L⁻¹ were unlikely to significantly impact osmoregulatory function in rainbow trout and kōura in Lake Rotorua.
A second experiment utilised intermittent flow respirometry to determine mass-specific metabolic oxygen consumption rates (MO₂) of rainbow trout, common bully, and kōura exposed to 2 mg Al L⁻¹ and diel pH fluctuations (pH 7–10) over 60 hours. It was expected that precipitation of dissolved aluminium onto the gill surface during pH transitions and/or binding of dissolved aluminium species could inhibit the respiratory gas exchange resulting in increased gill ventilation from hypoxic and hypercapnic conditions. There was a significant negative correlation (Pearson’s, r² = 0.34, P <0.001) between pH and MO₂, possibly indicating kōura were sensitive to the experimental conditions. However, there were no consistent trends in differences between control and treatment groups for any of the tested species. Data interpretation was hindered by the necessity to exclude samples from the rainbow trout and common bully control groups due to aberrations in the oxygen sensor data. However, the mean MO₂ was within expected ranges for rainbow trout and kōura, indicating that significant respiratory impacts were not occurring during the exposure period. Although definitive conclusions could not be made regarding changes to MO₂ in response to aluminium and diel pH cycling, it is unlikely that acute impacts would result from these conditions in the natural environment. From this research, it is concluded that the combined impacts of diel pH cycling and aluminium exposure at twice the current dosing rate (i.e., 1 mg Al L⁻¹) are unlikely to significantly impact respiratory and osmoregulatory function in fish and kōura in Lake Rotorua. There was some indication that at circumneutral pH and moderate aluminium concentrations (2 mg Al L⁻¹), particulate aluminium may cause erosional damage to kōura gill tissue. However, such conditions are highly unlikely to be encountered within the lake where the mean total aluminium concentrations are approximately one hundred times lower (0.02 mg Al L⁻¹). These experimental results are consistent with observations from the Al-dosed Utuhina stream, which show no evidence of effects on macroinvertebrate communities or kōura downstream of the Al input. Further investigation of aluminium exposure on more susceptible and less mobile life stages (e.g., larval rainbow trout) would help to define potential impacts and species tolerances. Further testing of potential impacts on gill tissues of kōura from particulate aluminium is also recommended.

text: Toxicological effects of aluminium in relation to diel pH changes on fish and kōura Since 2006, alum (aluminium sulphate; Al₂(SO₄)₃) has been applied to the Utuhina and Puarenga Streams at a targeted dose rate of 1 mg Al L⁻¹ to control phosphorus loading to Lake Rotorua. Alum dosing is widely used for water quality restoration and, under circumneutral pH (6-8), is considered to have no significant toxicological impacts at low to moderate (0.1–2 mg Al L⁻¹) concentrations. At circumneutral pH, alum forms aluminium hydroxide (AlOH₃), a white insoluble precipitate which adsorbs phosphorus, reducing its availability for phytoplankton growth. However, at high or low pH, monomeric and hydroxy aluminium species occur in varying proportions with respect to acidic (i.e., Al³⁺, AlOH²⁺, Al(OH)²⁺) and alkaline (i.e., Al(OH)₄⁻) conditions with increasing toxicity to aquatic organisms. 
Under typical conditions, the pH of Lake Rotorua is near pH 7, but due to its limited buffering capacity may reach pH 10 during intensive algal blooms. These diel increases in pH occur due to the photosynthetic uptake of CO₂ during the day, thereby increasing the environmental hydroxide concentration and raising the pH of the lake. At night, respiration releases CO₂, driving down the pH due to the formation of carbonic acid. Diel pH cycling has the potential to solubilise alum-derived aluminium, resulting in toxicological impacts on aquatic biota. Previous research has primarily focused on the toxicological impacts of aluminium under acidic or, more recently, alkaline conditions, however, potential impacts during transient exposure to alkaline pH have not been reported. 
The University of Waikato was contracted to investigate the effects of aluminium at 2 mg L⁻¹ in association with diel pH cycling on rainbow trout (Oncorhynchus mykiss), common bully (Gobiomorphus cotidianus) and kōura (Paranephrops planifrons) osmoregulation and respiration. Potential osmoregulatory effects were investigated by exposure of rainbow trout and kōura to aluminium at 2 mg L⁻¹ under diel pH cycling (pH 7–10) over 10 days. No significant differences between control and treatment groups were observed in either plasma and haemolymph osmolarity, haematocrit or haemoglobin concentration (Student’s t-test, P >0.05). A significant difference (Student’s t-test, P <0.05) in the mean cell haemoglobin concentration (MCHC) in the rainbow trout control group was attributed to erythrocyte swelling, suggesting a generalised stress-induced response rather than an impact from aluminium. Histological examination of kōura and rainbow trout gill tissue was also conducted, with abnormalities observed within both control and treatment groups for each species. A significant difference (Kolomogorov-Smirnov, P <0.05) was observed between kōura control and treatment groups, indicating that kōura gills may be more susceptible to erosional damage from precipitated aluminium hydroxide. It was concluded that diel pH cycling and exposure to 2 mg Al L⁻¹ were unlikely to significantly impact osmoregulatory function in rainbow trout and kōura in Lake Rotorua.
A second experiment utilised intermittent flow respirometry to determine mass-specific metabolic oxygen consumption rates (MO₂) of rainbow trout, common bully, and kōura exposed to 2 mg Al L⁻¹ and diel pH fluctuations (pH 7–10) over 60 hours. It was expected that precipitation of dissolved aluminium onto the gill surface during pH transitions and/or binding of dissolved aluminium species could inhibit the respiratory gas exchange resulting in increased gill ventilation from hypoxic and hypercapnic conditions. There was a significant negative correlation (Pearson’s, r² = 0.34, P <0.001) between pH and MO₂, possibly indicating kōura were sensitive to the experimental conditions. However, there were no consistent trends in differences between control and treatment groups for any of the tested species. Data interpretation was hindered by the necessity to exclude samples from the rainbow trout and common bully control groups due to aberrations in the oxygen sensor data. However, the mean MO₂ was within expected ranges for rainbow trout and kōura, indicating that significant respiratory impacts were not occurring during the exposure period. Although definitive conclusions could not be made regarding changes to MO₂ in response to aluminium and diel pH cycling, it is unlikely that acute impacts would result from these conditions in the natural environment. From this research, it is concluded that the combined impacts of diel pH cycling and aluminium exposure at twice the current dosing rate (i.e., 1 mg Al L⁻¹) are unlikely to significantly impact respiratory and osmoregulatory function in fish and kōura in Lake Rotorua. There was some indication that at circumneutral pH and moderate aluminium concentrations (2 mg Al L⁻¹), particulate aluminium may cause erosional damage to kōura gill tissue. However, such conditions are highly unlikely to be encountered within the lake where the mean total aluminium concentrations are approximately one hundred times lower (0.02 mg Al L⁻¹). These experimental results are consistent with observations from the Al-dosed Utuhina stream, which show no evidence of effects on macroinvertebrate communities or kōura downstream of the Al input. Further investigation of aluminium exposure on more susceptible and less mobile life stages (e.g., larval rainbow trout) would help to define potential impacts and species tolerances. Further testing of potential impacts on gill tissues of kōura from particulate aluminium is also recommended.

year: 2022

title: Are they really at risk? Students' stories of success.

authors: Gray, Sheridan

subjects: Student engagement

abstract: In 2011, as the year level dean for year 13, I was surprised and pleased to see a group of students complete their fifth year of secondary schooling, contrary to teacher expectations, and in spite of earlier signs of disengagement and struggle.  Such students are frequently labelled “at risk” in our secondary schools. Truancy, lack of achievement, conduct issues, learning difficulties and health problems are seen as indicators of an at risk student by teachers. 

Statistically in Aotearoa, Māori and Pasifika students and students from low socio-economic families tend to be overrepresented among disengaged or early leavers from secondary schools, and so being from these cultures, and being from a low socio-economic group becomes a “risk” factor.   This can lead to assumptions among teachers about the students’ families, how parents value education, and even about the capacity of these groups to be able to succeed in education.  A range of strategies and programmes have been implemented in an attempt to address these issues, including Te Kotahitanga, Ka Hikitia and the Pasifika Education Plan, Resource Teachers Learning and Behaviour, Restorative Practice, and more recently Positive Behaviour for Learning

While there has been a shift in such approaches from deficit of students to emphasising more positive attitudes in teachers, the perspectives of the students themselves are missing from the discussion about these issues.  This study asks students what factors helped them to stay, and to achieve at least a level one NCEA qualification

The findings show that retention and engagement of “at risk” students requires careful attention to the quality of relationships across the school community: students, teachers and parents. They discredit some commonly held assumptions that “at risk” students and their parents do not value education and that teachers cannot support these students sufficiently. These quality relationships are respectful, responsive and tenacious showing a high level of respect for and interest in the students that goes beyond a teaching and learning relationship.  It also suggests that the discourse of “risk” invites a disrespectful response to retention and engagement of students.

text: Are they really at risk? Students' stories of success. In 2011, as the year level dean for year 13, I was surprised and pleased to see a group of students complete their fifth year of secondary schooling, contrary to teacher expectations, and in spite of earlier signs of disengagement and struggle.  Such students are frequently labelled “at risk” in our secondary schools. Truancy, lack of achievement, conduct issues, learning difficulties and health problems are seen as indicators of an at risk student by teachers. 

Statistically in Aotearoa, Māori and Pasifika students and students from low socio-economic families tend to be overrepresented among disengaged or early leavers from secondary schools, and so being from these cultures, and being from a low socio-economic group becomes a “risk” factor.   This can lead to assumptions among teachers about the students’ families, how parents value education, and even about the capacity of these groups to be able to succeed in education.  A range of strategies and programmes have been implemented in an attempt to address these issues, including Te Kotahitanga, Ka Hikitia and the Pasifika Education Plan, Resource Teachers Learning and Behaviour, Restorative Practice, and more recently Positive Behaviour for Learning

While there has been a shift in such approaches from deficit of students to emphasising more positive attitudes in teachers, the perspectives of the students themselves are missing from the discussion about these issues.  This study asks students what factors helped them to stay, and to achieve at least a level one NCEA qualification

The findings show that retention and engagement of “at risk” students requires careful attention to the quality of relationships across the school community: students, teachers and parents. They discredit some commonly held assumptions that “at risk” students and their parents do not value education and that teachers cannot support these students sufficiently. These quality relationships are respectful, responsive and tenacious showing a high level of respect for and interest in the students that goes beyond a teaching and learning relationship.  It also suggests that the discourse of “risk” invites a disrespectful response to retention and engagement of students.

year: 2012