ERI Reports

Permanent URI for this collectionhttps://hdl.handle.net/10289/16658

ERI Reports are prepared by researchers affiliated with ERI to disseminate findings from externally funded research. ERI Reports are peer-reviewed and published on the University of Waikato Research Commons, making them credible, citable, and available as a public resource. They also serve to illustrate the diversity of research within ERI and the capabilities of ERI researchers.

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Alum dosing effects on fish and aquatic invertebrates: Utuhina Stream 2024
(Environmental Research Institute | Te Tumu Whakaora Taiao, The University of Waikato, 2025) Ling, Nicholas; Tempero, Grant Wayne
To reduce external phosphorus loading to Lake Rotorua, the Bay of Plenty Regional Council has been granted resource consent to dose the Utuhina Stream with alum (aluminium sulphate). Aluminium binds phosphorus, preventing its uptake by phytoplankton and thereby inhibiting growth. Aluminium forms monomeric species outside of circum-neutral pH (pH 68), and these species can disrupt osmoregulation and respiration of aquatic organisms. The alum dose rate to the Utuhina Stream is dependent on discharge, with a maximum application rate of 1 mg Al L-1. This report presents the results of an on-going assessment of the fish and aquatic macroinvertebrate communities of the Utuhina Stream for 2024. Macroinvertebrates, fish and kōura (freshwater crayfish; Paranephrops planifrons) were sampled from one control (site 1) and two treatment (sites 2 & 3) reaches of the Utuhina Stream. Common bully (Gobiomorphus cotidianus) were the dominant species of the fish community, with juvenile trout and kōaro (Galaxias brevipinnis) also captured. Kōura were present at all sites but variable in abundance. There was a notable decline in the semiquantitative macroinvertebrate community (for soft-bottomed streams; MCI-sb) score at Sites 1 and 3 in 2024 compared to long-term site averages, with Site 1 declining into the ‘poor’ category. Interannual variation in MCI-sb scores is typical for these reaches of the Utuhina Stream and have been attributed to flood-related disturbances to stream bank morphology and in-stream vegetative cover (Ling 2021). Tissue aluminium concentrations were determined from common bully (flesh, gill, liver) and kōura (flesh, gill, hepatopancreas) by inductively coupled plasma mass spectrometry (ICP-MS). There was some evidence of aluminium bioaccumulation in the liver tissues of common bully at Site 2, but overall concentrations were similar to long-term averages and there were no notable differences for the same tissues between sites. Kōura tissue aluminium concentrations for 2024 were similar to long-term averages across all tissues and sites. A small number of individuals had elevated gill concentrations at Site 3 compared to long-term average concentrations, but this is unlikely to result in harmful physiological impacts. The data presented in this report further supports the conclusion by Tempero and Ling (2024) that alum dosing does not appear to have a notable effect on the fish and kōura community and that site and interannual differences appear to be due to hydrological and habitat variability.
Benthic nutrient release from Auckland dune lakes
(Environmental Research Institute, The University of Waikato, 2025) Özkundakci, Deniz; Tempero, Grant Wayne
New Zealand’s freshwater lakes are under pressure from land use intensification, discharge of nutrient contaminants and over-allocation of groundwater resources. Dune lakes are comparatively rare ecosystems formed by wind-blown sand which creates depressions or water impoundments. Often isolated and diversity depauperate, their geomorphological features can make them particularly vulnerable to anthropogenic eutrophication. Ecological models provide a tool for assessing potential strategies for remediation of lake eutrophication. However, they require an understanding of the drivers of water quality decline, including external and internal nutrient loading. The University of Waikato was contracted by Auckland Council to assess lake littoral groundwater infiltration rates and sediment nutrient release rates in seven dune lakes to support the development of ecological models for the lakes. Littoral groundwater infiltration was measured using custom moulded clear acrylic domes fitted with valves which allowed water passage into an attached collection bag. The chambers were deployed in the winter and of late spring of 2023. Depending on lake size and site suitability, between one and four chambers were deployed in the littoral zone (generally ~0.5m depth) of each lake and left in place for 24 hours. Net groundwater efflux was not detected by any of the chambers, while groundwater infiltration rates ranged from 1.0–7.4 L m-2 day-1. Assessment of groundwater nutrient concentrations was not feasible due to the volume of the chamber (16 L) and the deployment period required to determine infiltration rates. Littoral groundwater infiltration likely constitutes a significant proportion of the inflow to these lakes, and rates appear to be volumetrically proportional to the linear distance to the catchment boundary from the point of sampling, and to variance in catchment rainfall. Littoral infiltration rates responded quickly (<24 hours) to total precipitation preceding sampling; however, this may be partially due to the higher-than-average rainfall and soil saturation during the 2023 survey period. Sediment nutrient release rates were determined using benthic incubation chambers deployed at or near the deepest point of each lake during the spring of 2023. Four dark chambers were deployed in each lake for between 32–68 hours, water samples were pumped from each chamber and analysed for dissolved nutrients. Lakes Kawaupaku, Ōkaihau, Te Kanae and Whatihua were strongly stratified with anoxic bottom waters and sediment nutrient release rates could not be determined. Bottom water samples taken at the time of chamber deployment in these lakes found ammonium and nitrate concentrations were high (>0.2 mg N L-1) but dissolved reactive phosphorus (DRP) concentrations were near or below detection limits (<0.004 mg P L-1); indicating that internal lake phosphorus loading was likely limited in comparison to nitrogen loading. The shallow, polymictic nature of the Tomarata, Spectacle and Slipper lakes provided more suitable conditions for determination of in situ sediment nutrient fluxes, although a second deployment in Lake Tomarata was conducted in August 2024. The measured nutrient flux rates, maximum nutrient flux rates and half saturation constants for ammonium and dissolved reactive phosphorus are presented in the table below. The low phosphorus release rates may be due to low external phosphorus loading, associated with episodic sediment loading from the mostly ephemeral surface inflows to the lakes. These findings align with previous work carried out in Lake Tomarata demonstrating the sedimental total phosphorus (TP) pool to have a low redox sensitive phosphorus fraction despite sediment iron content being reasonably high (Waters, 2022). Prolonged stratification of lakes Kawaupaku, Ōkaihau, Te Kanae and Whatihua provided limited opportunity to directly assess internal nutrient loading. However, external phosphorus loading to these lakes is likely to be constrained as they are primarily groundwater fed with small, ephemeral surface inflows. In addition, hypolimnetic DRP concentrations and sediment phosphorus release rates determined for lakes Tomarata, Slipper and Spectacle indicate that internal phosphorus loading is low compared to other New Zealand lakes. External nitrogen loading is likely to be more substantial than phosphorus loading, but internal loading also appears to be lower than average. These findings underscore the distinct processes driving nitrogen and phosphorus loading, and consequently nutrient concentrations in the lakes studied. They also provide data critical for the parameterisation of subsequent water quality models, which might be used to inform land use practices through comprehensive scenario testing of various management options.
Modifying hydrological regime and catchment land use to improve water quality in Lake Waikare: Modelled insights
(Environmental Research Institute, The University of Waikato, 2025) Prentice, Matthew James ; Özkundakci, Deniz
Effective management of eutrophication in large, shallow, lakes is particularly challenging, especially in catchments dominated by agricultural activities. These challenges are further exacerbated in lakes that have undergone significant hydrological and biogeochemical modification. In these systems, effective hydrological management strategies may involve increasing discharge rates to promote flushing and modifying lake depth to reduce the effects of wind-induced sediment resuspension, while effective biogeochemical modification may involve improving catchment management practices to reduce external nutrient loading. In this study, we present a modelling investigation of Lake Waikare, Waikato, New Zealand; a large (surface area: 34 km²), shallow (mean depth: 1.2 m), hypereutrophic lake that has experienced significant hydrological modification and water quality deterioration since the early 1900s.
Alum dosing effects on fish and aquatic invertebrates: Utuhina Stream 2021-2023
(Environmental Research Institute, The University of Waikato, 2024) Ling, Nicholas; Tempero, Grant Wayne
To reduce external phosphorus loading to Lake Rotorua, the Bay of Plenty Regional Council has been granted resource consent to dose the Utuhina Stream with alum (aluminium sulphate). Aluminium binds phosphorus, preventing its uptake by phytoplankton and thereby inhibiting growth. Aluminium forms monomeric species outside of circum-neutral pH (pH 6-8), and these species can disrupt osmoregulation and respiration of aquatic organisms. The alum dose rate to the Utuhina Stream is dependent on discharge, with a maximum application rate of 1 ppm aluminium. This report presents the results of an on-going assessment of the fish and aquatic macroinvertebrate communities of the Utuhina Stream for 2021–2023.
Alum dosing of Waitangi Stream: Biomonitoring of aluminium 2021-2023
(Environmental Research Institute, The University of Waikato, 2024) Tempero, Grant Wayne; Ling, Nicholas
Continuous alum dosing of the Waitangi Stream at Lake Rotoehu commenced in 2011 to reduce concentrations of dissolved reactive phosphorus in this inflow to the lake and improve water quality. The Bay of Plenty Regional Council contracted the University of Waikato to undertake monitoring of biota in the Waitangi Stream for potential impacts due to alum dosing. Macroinvertebrate community analysis and tissue aluminium concentrations in kōura (Paranephrops planifrons) and goldfish (Carassius auratus) have been undertaken annually since 2013 to determine the impacts and bioaccumulation of aluminium.
Variability in the trophic level index in Lake Rotoehu from 1990 to 2021
(Environmental Research Institute, The University of Waikato, 2025) Woelmer, Whitney; Özkundakci, Deniz
Setting an appropriate Trophic Level Index (TLI) target for lakes in the Rotorua Te Arawa region is critical for informing short- and long-term management decisions. Due to high variability in the observed TLI of Lake Rotoehu, coupled with contrasting understanding of historical water quality in the lake, the Bay of Plenty Regional Council requested a robust analysis of the drivers of the TLI over time to help inform the suitability of the current TLI target. To undertake this, we first quantified the uncertainty around the TLI in the 1990s, when the current TLI target was set based on the “best” observed water quality within the long-term monitoring program, to understand how a lower sampling frequency from 1990-2000 (~every 2-3 months) impacted TLI estimates. We found that while sampling fewer times in the year in the 1990s increased uncertainty around TLI estimates by 0.2-0.3 TLI units, a marked shift in water quality from a TLI of 3.6 in 1992 to 4.5 in 1993 remained evident. To understand if the main drivers affecting the TLI were different during the 1990s as opposed to later decades, we calculated the Pearson correlation coefficient between the TLI and several driver variables separately for each decade. Drivers in this analysis included meteorological variables, lake water level, and in-lake water quality not in the TLI calculation (e.g., bottom water nutrients, water temperature, stratification metrics), and the amount of aluminium sulphate dosed to the lake. While several variables were consistently important across all decades (e.g., bottom water nutrients, bottom water temperature, and mean monthly air temperature), average monthly water level and minimum windspeeds were only important in the 1990s, indicating that these variables had been related to major shifts in water quality seen during that time. Lastly, to better understand the relative importance of multiple drivers of the TLI and whether this importance changes over time, we conducted a moving window analysis. We fit autoregressive models, meaning the models included the previous month’s TLI estimate, as well as a single driver variable over a moving window of ~8 years, where each window moved forward one month at a time. We found that air temperature, bottom water temperature, and bottom water dissolved reactive phosphorus (DRP) were most often the top predictors of the TLI. However, the relative importance of average monthly water level increased sharply to the most important driver during a time period which also corresponded to very high water levels. Additionally, examination of model parameters over the simulation period demonstrated that the strength and magnitude of the relationship between the TLI and individual drivers changed over time, indicating that that relationships are not fixed through time. Overall, this work highlights the importance of re-evaluating the underlying relationships between the TLI and drivers over time, emphasising the dynamic nature of Lake Rotoehu. We demonstrate a clear shift in water quality between 1992 and 1993, likely driven by low water levels and windspeeds, which may have induced a pattern of increased external loading that still exists. Importantly, many of the variables which emerged as important for the TLI (water level, windspeed) will continue to vary with changing climate and are outside of the control of management. In light of this, while the current TLI target (3.9) may be feasible for Lake Rotoehu given historical observations and possible reference conditions, achieving this target consistently may be very difficult going forward due to catchment and climate pressures which have put Lake Rotoehu outside of an undisturbed reference state. This work can be built upon through future analyses which continue quantifying the changing relationships between the TLI and drivers over time, increasing the use of high-frequency buoy data to better inform water quality dynamics at shorter time scales, and testing our understanding of the drivers of water quality through predictions. The overall aim for future research would therefore be to establish water quality targets that not only align with community aspirations but are also technically feasible, especially in light of global change.
Ōhau Channel diversion wall: 7-year review: Water quality review and modelling
(Environmental Research Institute, The University of Waikato, 2024) Prentice, Matthew James; Özkundakci, Deniz
Lake Rotoiti experienced significant degradation in water quality from the 1960s to the early 2000s due to nutrient-laden waters flowing from Lake Rotorua via the Ōhau Channel. To address this, an inlake diversion wall was constructed in 2007/2008 to block the influx of these nutrient-rich waters. However, during this period, water quality in Lake Rotorua also improved due to enhanced catchment management practices and alum dosing. Consequently, there is now a question of whether and to what extent the diversion wall is still necessary to prevent water quality deterioration in Lake Rotoiti, at its current Trophic Level Index (TLI) and target TLI of 3.5. This report presents the findings and implications of a comprehensive study commissioned by the Bay of Plenty Regional Council to evaluate the impact of the Ōhau Channel diversion wall on the water quality of Lake Rotoiti, New Zealand. The study, guided by specific research questions outlined in the “Terms of Reference: Ōhau wall: 7-year review”, aimed to assess the effectiveness of the wall in improving water quality, its influence on achieving TLI targets, and its impact on the quality of the Kaituna River. Additionally, the study investigated the potential consequences of removing the diversion wall, considering the altered water residence time and its effects on bottom water dissolved oxygen (DO) levels. An assessment of the holes in the diversion wall was also carried out to understand the amount of water leaking through the wall into Lake Rotoiti. To address the above research questions, this study consisted of three main components: 1) analysis of observed changes in water quality, 2) lake system modelling, and 3) assessment of holes in the diversion wall. Data analysis involved statistical analyses to determine differences in water quality pre- and post-wall construction. Lake system modelling included configuring a 3-D hydrodynamiconly model to assess for variation in hydrodynamics, and a coupled hydrodynamic-ecological model to assess for variation TLI with and without the wall using scenario simulations over a prolonged period (i.e., 19 years for the hydrodynamic model; 8 years for the hydrodynamic-ecological model). Assessment of wall holes involved data analysis and hydrodynamic model scenario testing to evaluate their impact on Lake Rotoiti. The data analysis of existing water quality data for Lake Rotoiti, employing a three-step approach (in increasing levels of complexity and inference), revealed nuanced insights into the impacts of the Ōhau Channel diversion wall. While descriptive statistics (i.e., approach 1) indicated overall improvement in water quality post-wall construction in Lake Rotoiti, correlation analysis (i.e., approach 2) between water quality in Lake Rotorua and Rotoiti suggests limited statistical significance in observed differences, except for Secchi depth, indicating altered connectivity between Lake Rotorua and Rotoiti. An intervention analysis (i.e., approach 3), employing interrupted time series analysis, detected significant step changes in total nitrogen (TN), Secchi depth, and TLI post-wall construction, suggesting immediate positive effects on lake water quality persisting throughout the study period. The estimated improvements due to the diversion wall were a decrease in TN by 203 mg m-3, an increase in Secchi depth by 2.5 m, and a decrease in TLI by 0.59 units. The data analysis supports the long-held observations of the Lake Rotoiti community, who have noticed a visible improvement in water quality immediately following the construction of the diversion wall. The data analysis revealed that the diversion wall has had no significant impact on bottom water DO demand in Lake Rotoiti, as measured by volumetric hypolimnetic oxygen demand, which remained largely unchanged. Any yearto-year variations are likely attributed to changes in prevailing in-lake and meteorological conditions. Hydrodynamic model simulations revealed that the wall was effective in reducing the accumulation of Ōhau Channel inflow in the system, increasing the fraction of Ōhau Channel inflow short-circuited down the Kaituna River and, consequently, increasing the residence time of Lake Rotoiti. In terms of accumulation of Ōhau Channel-derived water in Lake Rotoiti, the wall resulted in a substantial reduction as evidenced by an annual cumulative contribution of Ōhau Channel water to Lake Rotoiti of 22.0% without a wall in place, but 0.3% with a wall in place. Concerning the fraction of Ōhau Channel-derived water short-circuited down the Kaituna River, the wall resulted in a substantial increase, as evidenced by the proportion of Ōhau Channel water being diverted down the Kaituna River being 55.2% without a wall in place, but 99.3% with a wall in place. Regarding the residence time in Lake Rotoiti, the wall resulted in a substantial increase, i.e., a factor of 3.3, as evidenced by a residence time of 8.2 years without a wall in place, but 26.9 years with a wall in place. Coupled hydrodynamic-ecological model simulations revealed the removal of the wall lead to a small deterioration of water quality in Lake Rotoiti, which could be mitigated with improved water quality in the Ōhau Channel inflow. The various scenario testing revealed that removal of the wall alongside a maximum TLI in Lake Rotorua of ~4.3 would likely be required to maintain the current TLI in Lake Rotoiti; however, removal of the wall alongside a maximum TLI in Lake Rotorua of ~4.0 would be required to maintain the current TLI and each of Trophic Level nitrogen, Trophic Level phosphorus, and Trophic Level chlorophyll a. Further, removal of the wall alongside even the most ambitious reduction in maximum TLI in Lake Rotorua (i.e., 3.8) would require additional water quality management in Lake Rotoiti to achieve the target TLI in Lake Rotoiti of 3.5. The analysis of available data on the holes in the diversion wall indicates that despite a relatively small number of estimated holes in the wall, the leakage of Ōhau Channel water into Lake Rotoiti is appreciable; i.e., assuming a total of 100 holes along the length of the diversion wall, approximately 3.3% of the Ōhau Channel water was estimated to leak through the holes into Lake Rotoiti. This percentage increased to 9.8% of the Ōhau Channel water when the total number of holes was assumed to be 300. These discharge rates compare well with the hydrodynamic modelled output, where a single 1 × 100-meter hole (the finest scale hole possible within our model grid) in the Ōhau Channel diversion wall was shown to reduce the effectiveness of the wall in preventing the accumulation of Ōhau-derived water within the lake by 29.3-55.0%. However, the study's estimates are conservative and limited by the model resolution. Given uncertainties in the number of holes, the focus was on estimating water discharge rather than assessing nutrient load or water quality impacts. Overall, the evaluation of water quality in Lake Rotoiti, including a systematic analysis of long-term datasets and detailed 3-D hydrodynamic-ecological modelling, shows that improvements in water quality in the lake were evident following the construction of the diversion wall. This study shows that the Ōhau Channel diversion wall was critical in preventing the degradation of Lake Rotoiti, but meeting the TLI target in the lake will be challenging if the removal of the wall occurs, even if TLI targets in Lake Rotorua are met.
Extent of seagrass in Tauranga Harbour: a comparison of satellite automated classification versus manual delineation of aerial imagery
(Environmental Research Institute, The University of Waikato, 2024-11-28) Shao, Zhanchao; Vaassen, Sanne; Pullig, Mariane C.
This report outlines a comprehensive analysis of seagrass extent in Tauranga Harbour, New Zealand, using advanced remote sensing techniques. It compares two key methods: satellite-based supervised classification using Random Forest, and manual delineation via aerial photography. The research focuses on mapping the spatial and temporal changes in seagrass habitats, particularly the native species Zostera muelleri, from 1959 to 2024. Complementary to the satellite-based classification method, an easy-to-use graphical user interface (GUI) was developed, enabling users to efficiently access satellite imagery and generate detailed habitat maps. The supervised classification using Random Forest proved effective for detecting seagrass habitats, achieving high accuracy (0.92 for Sentinel-2 and 0.88 for Landsat imagery). Despite occasional misclassifications, particularly in areas with high chlorophyll concentrations (i.e., the Tauranga Harbour sub-estuaries), the method provided a more time-efficient and scalable alternative to manual delineation. Aerial photography and manual mapping served as an important comparison but are less efficient in capturing less visible seagrass areas in deeper water or fragmented meadows.
Operational forest restoration plan for Kukutaaruhe Gully: Part 2
(Environmental Research Institute, the University of Waikato, 2020-10) Elliot Noe, Elizabeth; Wallace, Kiri Joy; Cornes, Toni; Kirkby, Catherine L.
Kukutaaruhe Gully is a minor branch of Hamilton’s extensive gully system, and runs from the corner of Bankwood and Clarkin Road, behind Fairfield College, connecting with Donny Park in the north and out into the Waikato River. The Kukutaaruhe Education Trust was established to support the implementation of the Fairfield Project, which is a partnership between Ngati Wairere, local community and Fairfield College. The project’s goals include the establishment of an ecological and environmental education centre on the approximately 12 ha of land behind Fairfield College and restoration of the adjacent Kukutaaruhe Gully. In 2019, the University of Waikato’s Environmental Research Institute was contracted by the Kukutaaruhe Education Trust to create an Operational Forest Restoration plan for Kukutaaruhe Gully. This is one in a three-part series created together under one contract: • Part 1 of 3 is an Overview of the Kukutaaruhe Gully Restoration Initiative • Part 2 of 3 is this document, the Operational Forest Restoration plan for Kukutaaruhe Gully • Part 3 of 3 is an Ecological Restoration Plan Template.
Overview of the Kukutaaruhe Gully restoration initiative: Part 1
(Environmental Research Institute, the University of Waikato, 2020-10) Elliot Noe, Elizabeth; Wallace, Kiri Joy; Cornes, Toni; Kirby, Catherine L.
Kukutaaruhe Gully is a minor branch of Hamilton’s extensive gully system, and runs from the corner of Bankwood and Clarkin Road, behind Fairfield College, connecting with Donny Park in the north and out into the Waikato River. The Kukutaaruhe Education Trust was established to support the implementation of the Fairfield Project, which is a partnership between Ngati Wairere, local community and Fairfield College. The project’s goals include the establishment of an ecological and environmental education centre on the approximately 12 ha of land behind Fairfield College and restoration of the adjacent Kukutaaruhe Gully. In 2019, the University of Waikato’s Environmental Research Institute was contracted by the Kukutaaruhe Education Trust to create an Overview of the Kukutaaruhe Gully restoration initiative. This is one in a three-part series created together under one contract: • Part 1 of 3 is the first document presented here, an Overview of the Kukutaaruhe Gully Restoration Initiative • Part 2 of 3, the Operational Forest Restoration plan for Kukutaaruhe Gully • Part 3 of 3 is an Ecological Restoration Plan Template.
Development of a molecular tool to identify brown bullhead catfish (Ameiurus nebulosus) from environmental DNA in water
(Environmental Research Institute, The University of Waikato, 2020-08-21) Hicks, Brendan J.; Cursons, Ray
The aim of this work was to develop a molecular tool to positively identify brown bullhead catfish using environmental DNA (eDNA) that is suspended within the water column. The project had five main objectives: 1) to develop a protocol for the collection of eDNA, 2) to select and test primer sets that are specific to brown bullhead catfish, 3) to optimise DNA extraction and amplification, 4) to validate the methodology through sequencing the amplified DNA, and 5) to evaluate its sensitivity by sampling at various sites that had a range of catfish abundances. Water was sampled from Lake Rotoiti from a boat with a 1 litre labelled plastic container attached to a telescopic pole, retrieving water samples about 30 cm above the lake bottom in about 2 m of water depth and from deeper water. Each container was deployed container-opening facing down, and on reaching the desired collection depth, the opening was rotated uppermost to allow the entry of water. The full container was then pulled back to the surface, a plastic screw cap firmly screwed onto the container, and then subsequently placed in a chilly bin on a 20-cm layer of crushed ice. The collection was recorded on a GPS instrument.
Characteristics of sub-surface sediments in southern Stella Passage, Tauranga Harbour
(Environmental Research Institute, The University of Waikato, 2019) Moon, Vicki G.; De Lange, Willem P.
The Port of Tauranga is considering port developments that would require capital dredging of a section of the southern Stella Passage to achieve depths comparable to the northern Stella Passage. Seismic profiles, core samples, and CPT data were collected by the University of Waikato and OPUS for the area impacted by proposed development. The core samples were analysed for sediment texture, including assessment of the fines (silt + clay) content. Four main stratigraphic units were identified from the available data. These were, in order of increasing stratigraphic depth and age: Holocene sand; Pleistocene alluvial fan; Pleistocene organic silt; and Pleistocene terrestrial and shallow marine sand. In general, the fines content increased with depth and age. Younger units thin southwards along Stella Passage, resulting in increasing fines content southwards along the channel.
Puarenga Stream alum dosing – summary of effects on lake biota 2013/2014
(Environmental Research Institute, The University of Waikato, 2014-11) Ling, Nicholas
Continuous alum dosing of the Puarenga Stream commenced in early 2010 to reduce inflows of dissolved reactive phosphorus to Lake Rotorua. Analyses of bioaccumulation in the tissues of macrobiota were undertaken in February 2013 and February 2014 for comparison to comparable samples obtained prior to and shortly after the commencement of alum dosing. No significant effects of alum dosing could be distinguished. Bioavailable aluminium in the vicinity of Sulphur Bay appears to be primarily influenced by the major geothermal activity of this region. No significant differences in aluminium bioaccumulation were observed in any species compared to samples obtained prior to the commencement of alum dosing. Continuous alum dosing of the Puarenga Stream since 2010 apparently has not resulted in adverse effects to Lake Rotorua shoreline biota nor caused any apparent increase in aluminium bioaccumulation in lake biota in the vicinity of Sulphur Bay.
Utuhina Stream monitoring 2014: Effects of continuous alum dosing on fish and aquatic invertebrates
(Environmental Research Institute, The University of Waikato, 2015) Ling, Nicholas
This report presents the results of an ongoing assessment of the fish and aquatic macroinvertebrate communities of the Utuhina Stream from 2006 to 2014, and an assessment of the bioavailability of aluminium in fish and koura to satisfy annual resource consent conditions 9.6, 9.8 and 9.7, respectively, for the discharge of alum. Macroinvertebrates, fish and koura were sampled from one control and two treatment reaches of the Utuhina Stream in August 2014. Catch rates for common bully, juvenile trout and koura have fluctuated across all sites since monitoring began in 2006. Common bully, koura and juvenile trout were present at all sites. Differences in species abundance compared with previous years is most likely due to flood related disturbances to stream bank morphology and vegetative cover. No obvious effects of alum dosing on stream fish or macroinvertebrate communities were observed.
Assessing effects of changes to nutrient loads on Lake Tarawera water quality: Model simulations for 2010 to 2020
(Environmental Research Institute, The University of Waikato, 2020-12) Abell, Jonathan Michael; McBride, Chris G. ; Baisden, W. Troy
Lake Tarawera is a nationally significant lake that is highly valued by tangata whenua, local residents and the regional community. Monitoring shows that lake water quality does not presently meet the target, based on a Trophic Level Index (TLI) value of 2.6 identified in the Tarawera Lakes Restoration Plan1. Between 2010 and 2020 annual observed TLI was frequently as high as 2.9. Managing nutrient loads to the lake is necessary to achieve desired lake water quality and interim nutrient reduction targets have been established. An objective of this study was to evaluate these targets by improving estimates of ‘sustainable nutrient loads’, which are the external loads of nitrogen and phosphorus that would result in meeting the TLI target.
Catchment and lake water quality modelling to assess management options for Lake Rerewhakaaitu
(Environmental Research Institute, The University of Waikato, 2020) Cho, Eunju; Hamilton, David P.; McBride, Chris G.
Lake Rerewhakaaitu in the Bay of Plenty Region of North Island, has one of the most intensively farmed lake catchments in New Zealand. Nitrate concentrations in two surface stream inflows to the lake show substantial and statistically significant increases, between 1995 and 2015, however, lake water quality has remained relatively stable. The lake is polymictic (i.e., it mixes frequently) and is partly perched, with an effective hydrological catchment of approximately 10% of the surface topographic catchment. We used the hydrodynamic-ecological model DYRESM-CAEDYM to examine the relationship between inflow quantity and quality, and lake water quality. A groundwater model (MODFLOW) provided groundwater discharge values from the hydrologically effective catchment, to the lake model (DYRESM-CAEDYM). The model successfully reproduced the magnitude and dynamics of field measurements, as evidenced by low statistical error. Based on a novel uncertainty analysis that allows for assessment of forcing factors that contribute to model error, a component of the statistical error was identified to be due to lake water level variations, which was attributed to ecological changes in the littoral (shallow-water) zone of the lake. The calibrated model was used with a set of scenarios to examine land use change within the effective hydrological catchment, as well as climate change. Establishment of the lake model was subject to several areas of substantial uncertainty, including derivation of stream inflows by statistical modelling (rather than direct observation), hydrological uncertainty with regard to drainage pathways in the lake catchment, and reliability of some nutrient measurements in the lake and streams. Nevertheless, the present model can be considered among the most sophisticated tools available with which to inform lake management decisions. Model results suggest that improved land management efforts within the wider topographic catchment will have only minor impacts on Lake Rerewhakaaitu water quality, but within the hydrologically effective catchment land use improvements to decrease losses of nitrogen and phosphorus to the lake will be important. Maintaining and/or enhancing the forested area within the hydrologically effective catchment and potentially retiring (to indigenous vegetation) some of the area, as well as maintaining the riparian buffer of the lake, will help to maintain water quality of Lake Rerewhakaaitu. The model predicted that a future warmer climate would likely increase the duration of temperature stratification in the water column, leading to more deoxygenation of bottom waters and a decline in water quality. Offsetting this with maintaining and enhancing vegetation in the riparian area and hydrologically effective catchment may help to offset these effects.
Estimated catchment loads of nitrogen and phosphorus to the Rotorua Te Arawa Lakes
(Environmental Research Institute, The University of Waikato, 2021) McBride, Chris G.; MacCormick, Alastair; Verburg, Piet
The Rotorua Te Arawa Lakes are central to the identity of their region, of immense historical and cultural importance, and provide ecosystem services that underpin biodiversity, conservation and socioeconomic aspirations of the community. The diversity of water quality in the lakes reflects their catchments, which are diverse in topography, hydrogeology and intensity of land use, ranging from the largely undeveloped land around lakes Tikitapu and Okataina, to highly developed forestry and pastoral land around lakes Rerewhakaaitu, Rotorua and Okaro. Lake water quality is strongly linked to nutrients received by each lake from surface flows and groundwater springs. It therefore follows that management of lake water quality requires a good understanding of nutrient loads derived from the landscape, as does the assessment or prediction of the in-lake effects of catchment-based management initiatives aimed at improving lake water quality.
Lake water quality modelling to assess management options for Lake Hayes
(Environmental Research Institute, The University of Waikato, 2019) McBride, Chris G.; Muraoka, Kohji; Allan, Mathew Grant
Lake Hayes is an important ecological, historical and cultural asset to the Otago Region. The lake and its catchment have been substantially altered from their natural condition, including conversion of the catchment from forest to pasture, invasion of the lake by non-native macrophytes, blooms of cyanobacteria (blue-green algae) and lake Trophic Level Index has increased over recent years (Figure A). Since 2010 the lake has been characterised by very poor water quality and pronounced summer algal blooms. This has attracted public attention and provided impetus from community and stakeholders to assess available management options for restoring water quality in the lake. This report examines the drivers of poor water quality and associated algal blooms in the lake, and assesses various management options that have been either specifically proposed for Hayes, or have proven effective for other lakes in New Zealand and globally. Here we report on monitoring undertaken by Otago Regional Council in the catchment (surface inflows) and in the lake. Primarily, we apply state-of-the-art computer models to simulate physical, chemical, and biological processes within the lake. These simulations are then used to evaluate a range of management scenarios to provide guidance on the likely effects of management options.
Seasonal changes in phytoplankton nutrient limitation: Lake Rotorua
(Environmental Research Institute, The University of Waikato, 2020) Tempero, Grant Wayne
The management of macronutrient availability is central for reducing harmful algal blooms and the restoration of aquatic ecosystems. While there is some dispute as to the need for phosphorus (P) only control versus P and nitrogen (N) control, scientific opinion generally supports dual nutrient control in New Zealand lakes. Previous nutrient limitation studies of Lake Rotorua conducted during the 1970s and 1980s reported N limitation to varying degrees. This period coincided with the disposal of sub-optimally treated municipal wastewater to the lake, resulting in significant P loading and resultant algal blooms. Land disposal of wastewater was initiated in 1991 reducing nutrient loads to the lake, however, no further nutrient limitation studies were conducted until the summer of 2004 when N and P co-limitation was reported. From the mid-2000s water quality improved from a Trophic Lake index (TLI) of approximately 4.8 to 4.2, a change likely driven, in part, by sediment P depletion following the change to land disposal of wastewater and the initiation of alum dosing in 2006.
Waiwhakareke Natural Heritage Park 2018 long-term plot monitoring: Report on ecological restoration progress
(Environmental Research Institute, The University of Waikato, 2000) Farnworth, Bridgette; Wallace, Kiri Joy; Cornes, Toni S.
This report was requested by Tui 2000 Inc. and the Hamilton City Council (HCC) as a means of tracking terrestrial restoration progress at Waiwhakareke Natural Heritage Park (WNHP). WNHP is a cutting-edge urban ecological restoration project in which ecosystems representative of the Waikato region are being reconstructed from scratch on public land (formally pastoral land) in Kirikiriroa Hamilton. Large-scale projects of this nature are becoming more common around the globe due to growing emphasis on restoring nature in urban areas. While this report quantifies the remarkable ecological restoration success achieved at WNHP though investments by Tui 200 Inc., HCC and other partners over the years, it also contributes to scientific theory. Ecological restoration is a newly developing scientific field and hence WNHP presents a unique opportunity for ecologists to improve restoration practice and also learn from the results.

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