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: Sedimentation And Hydrodynamics of Whitianga Estuary

authors: Reeve, Glen M.D

subjects: Hydrodynamics

abstract: Whitianga Estuary is a bayhead barrier type estuary located on the east of the Coromandel Peninsula, North Island, New Zealand. The catchment has undergone many land-use changes since pre-European settlement. In some areas of the catchment land-use has changed from native forest to grasslands to forestry and back to pasture. These changes in catchment land-use all contribute to increased sedimentation into the estuary. Development of the estuary itself has also occurred in recent times. Much growth has been focussed around the estuary due to Whitianga town-ship having a large boating community, and includes a 170 berth marina and wharf situated at
the tidal inlet entrance to the estuary. These, and the extensive canal development engineering works can have substantial impacts on the
sedimentation regime, and may modify tidal circulation, flushing, and sediment deposition within the estuary.

The principle aim of this research is to assess hydrodynamics and sedimentation of the estuary for future management and development purposes, and also to model different scenarios in order to determine the most cost effective, and least obtrusive design for a proposed boat-ramp and
approach channel near the marina.

To determine sedimentation rates, sediment cores from four locations were collected to depths of 1 m. Coring locations were chosen based on
preliminary model run results, selecting areas that appeared to be long-term sediment sinks of a stable nature. Cores were divided into 10 mm sections and prepared for 210Pb dating and heavy metal analysis, to make an assessment of the vertical sedimentation rates. Recent sedimentation rates were found to be as high as 9 mm/yr post-1950s and past sedimentation rates
as high as 30 mm/yr pre-1950s. The use of heavy metal analysis for dating proved difficult as the background levels of the conservative elements used to normalise results varied, making the geochemical analysis approach inappropriate.

As bathymetry is one of the most important aspects of modelling, a large amount of surveying was undertaken for this study. LiDAR, singlebeam data, and recent rectified aerial photographs were interpreted for the creation of a
bathymetric grid file to be used for hydrodynamic modelling of the estuary.

The 3DD numerical model was used to determine tidal flows and current velocities. From this initial hydrodynamic model a particle-tracking model was created to determine sediment transport pathways within the estuary. From the initial 20 m model it was then possible to create a number of nested model grids for the purpose of determining the best practice scenario for the
creation of a proposed boat ramp and associated approach channel near the harbour entrance. Hydrodynamic results suggest that residual circulation in Whitianga Estuary is nearly in balance, with a low ebb tidal domination present. Particle tracking results suggest that sediment entrained and carried into and within the estuary will accumulate on the intertidal flats. Sediment
transport modelling indicates that the impact of a proposed boat-ramp will result in sedimentation of the dredged approach channel due to reductions in residual and tidal velocities.

text: Sedimentation And Hydrodynamics of Whitianga Estuary Whitianga Estuary is a bayhead barrier type estuary located on the east of the Coromandel Peninsula, North Island, New Zealand. The catchment has undergone many land-use changes since pre-European settlement. In some areas of the catchment land-use has changed from native forest to grasslands to forestry and back to pasture. These changes in catchment land-use all contribute to increased sedimentation into the estuary. Development of the estuary itself has also occurred in recent times. Much growth has been focussed around the estuary due to Whitianga town-ship having a large boating community, and includes a 170 berth marina and wharf situated at
the tidal inlet entrance to the estuary. These, and the extensive canal development engineering works can have substantial impacts on the
sedimentation regime, and may modify tidal circulation, flushing, and sediment deposition within the estuary.

The principle aim of this research is to assess hydrodynamics and sedimentation of the estuary for future management and development purposes, and also to model different scenarios in order to determine the most cost effective, and least obtrusive design for a proposed boat-ramp and
approach channel near the marina.

To determine sedimentation rates, sediment cores from four locations were collected to depths of 1 m. Coring locations were chosen based on
preliminary model run results, selecting areas that appeared to be long-term sediment sinks of a stable nature. Cores were divided into 10 mm sections and prepared for 210Pb dating and heavy metal analysis, to make an assessment of the vertical sedimentation rates. Recent sedimentation rates were found to be as high as 9 mm/yr post-1950s and past sedimentation rates
as high as 30 mm/yr pre-1950s. The use of heavy metal analysis for dating proved difficult as the background levels of the conservative elements used to normalise results varied, making the geochemical analysis approach inappropriate.

As bathymetry is one of the most important aspects of modelling, a large amount of surveying was undertaken for this study. LiDAR, singlebeam data, and recent rectified aerial photographs were interpreted for the creation of a
bathymetric grid file to be used for hydrodynamic modelling of the estuary.

The 3DD numerical model was used to determine tidal flows and current velocities. From this initial hydrodynamic model a particle-tracking model was created to determine sediment transport pathways within the estuary. From the initial 20 m model it was then possible to create a number of nested model grids for the purpose of determining the best practice scenario for the
creation of a proposed boat ramp and associated approach channel near the harbour entrance. Hydrodynamic results suggest that residual circulation in Whitianga Estuary is nearly in balance, with a low ebb tidal domination present. Particle tracking results suggest that sediment entrained and carried into and within the estuary will accumulate on the intertidal flats. Sediment
transport modelling indicates that the impact of a proposed boat-ramp will result in sedimentation of the dredged approach channel due to reductions in residual and tidal velocities.

year: 2008

title: Developing an integrated ocean observing system for New Zealand

authors: O'Callaghan, J

subjects: Science & Technology

abstract: New Zealand (NZ) is an island nation with stewardship of an ocean twenty times larger than its land area. While the challenges facing NZ's ocean are similar to other maritime countries, no coherent national plan exists that meets the needs of scientists, stakeholders or kaitiakitanga (guardianship) of NZ's ocean in a changing climate. The NZ marine science community used the OceanObs'19 white paper to establish a framework and implementation plan for a collaborative NZ ocean observing system (NZ-OOS). Co-production of ocean knowledge with Māori will be embedded in this national strategy for growing a sustainable, blue economy for NZ. The strengths of an observing system for a relatively small nation come from direct connections between the science impetus through to users and stakeholders of an NZ-OOS. The community will leverage off existing ocean observations to optimize effort and resources in a system that has historically made limited investment in ocean observing. The goal of the community paper will be achieved by bringing together oceanographers, data scientists and marine stakeholders to develop an NZ-OOS that provides best knowledge and tools to the sectors of society that use or are influenced by the ocean.

text: Developing an integrated ocean observing system for New Zealand New Zealand (NZ) is an island nation with stewardship of an ocean twenty times larger than its land area. While the challenges facing NZ's ocean are similar to other maritime countries, no coherent national plan exists that meets the needs of scientists, stakeholders or kaitiakitanga (guardianship) of NZ's ocean in a changing climate. The NZ marine science community used the OceanObs'19 white paper to establish a framework and implementation plan for a collaborative NZ ocean observing system (NZ-OOS). Co-production of ocean knowledge with Māori will be embedded in this national strategy for growing a sustainable, blue economy for NZ. The strengths of an observing system for a relatively small nation come from direct connections between the science impetus through to users and stakeholders of an NZ-OOS. The community will leverage off existing ocean observations to optimize effort and resources in a system that has historically made limited investment in ocean observing. The goal of the community paper will be achieved by bringing together oceanographers, data scientists and marine stakeholders to develop an NZ-OOS that provides best knowledge and tools to the sectors of society that use or are influenced by the ocean.

year: 2019-03-26