Science and Engineering Papers

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This collection houses research from the School of Science and from the School of Engineering at the University of Waikato.

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The role of mangrove fringe areas in providing feeding habitat for the New Zealand eagle ray (Myliobatis tenuicaudatus)
(Environmental Research Institute, The University of Waikato, 2018) Cadwallader, Helen Frances; Fernihough, G; Ross, Philip M.; Francis, M; Battershill, Christopher N.
This report details the results of an investigation into the use of mangrove fringe habitat by the eagle ray Myliobatis tenuicaudatus. The study was conducted in Matua estuary, Tauranga Harbour, and examined differences in the use of natural mangrove fringe vs. trimmed (mangrove removal and maintenance) mangrove fringe areas by rays. The use of these areas as feeding habitat was determined by quantification of feeding excavations.
Integration of stereo vision system calibration and kinematic calibration for an autonomous kiwifruit harvesting system
(Springer Nature, 2022) Au, Chi Kit; Lim, Shen Hin; Duke, Mike; Kuang, Ye Chow; Redstall, Michael; Ting, Canaan
Stereo vision system and manipulator are two major components of an autonomous fruit harvesting system. In order to raise the fruit-harvesting rate, stereo vision system calibration and kinematic calibration are two significant processes to improve the positional accuracy of the system. This article reviews the mathematics of these two calibration processes and presents an integrated approach for acquiring calibration data and calibrating both components of an autonomous kiwifruit harvesting system. The calibrated harvesting system yields good positional accuracy in the laboratory tests, especially in harvesting individual kiwifruit. However, the performance is not in line with the outcomes in the orchard field tests due to the cluster growing style of kiwifruit. In the orchard test, the calibrations reduce the fruit drop rate but it does not impressively raise the fruit harvesting rate. Most of the fruit in the clusters remain in the canopy due to the invisibility of the stereo vision system. After analyzing the existing stereo vision system, a future visual sensing system research direction for an autonomous fruit harvesting system is justified.
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.
Fatty acid biomarkers reveal landscape influences on linkages between aquatic and terrestrial food webs
(Ecological Society of America, 2025) Burdon, Frank; Sargac, Jasmina; Ramberg, Ellinor; Popescu, Darmina; Bradu, Corina; Forio, Marie A.E.; Witing, Felix; Kupilas, Benjamin; Lau, Danny C.P.; Volk, Martin; Rîşnoveanu, Geta; Goethals, Peter; Friberg, Nikolai; Johnson, Richard K.; McKie, Brendan
Stream and riparian habitats are meta-ecosystems that can be strongly connected via the emergence of aquatic insects, which form an important prey subsidy for terrestrial consumers. Anthropogenic perturbations that impact these habitats may indirectly propagate across traditional ecosystem boundaries, thus weakening aquatic-terrestrial food web linkages. We investigated how algal production, aquatic invertebrates, and terrestrial spiders influence cross-ecosystem connectivity in temperate streams across four European catchments with varying levels of human disturbance. We used fatty acid biomarkers to measure putative aquatic linkages to riparian spiders. Variation-partitioning analysis indicated that aquatic insect dispersal traits explained a relatively large proportion of variability in the fatty acid profile of spiders. Trophic connectivity, as measured by the proportion of the polyunsaturated fatty acid eicosapentaenoic acid (EPA) and the ratio of EPA to its chemical precursor, alpha-linolenic acid (ALA), was positively associated with abundances of “aerial active” dispersing aquatic insects. However, this positive influence was also associated with changes in environmental context and arachnid beta diversity. Structural equation modeling disentangled how aquatic insect communities influence trophic connectivity with riparian predators after accounting for biological and environmental contingencies. Our results show how subsidies of stream insects are a putative source of essential fatty acids for adjacent terrestrial food webs. Catchment-wide impacts indirectly propagated to the local scale through impacts on aquatic invertebrate communities, thus affecting stream-riparian food webs. Increased riparian tree cover enhanced stream insect subsidies via dispersal traits despite reducing aquatic primary production through shading. Consequently, ecosystem properties such as woody riparian buffers that increase aquatic-terrestrial trophic connectivity have the potential to affect a wide range of consumers in modified landscapes.
Feasibility study of green hydrogen to decarbonise New Zealand’s industries
(2024) Walmsley, Michael R.W.; Chong, Daniel; Atkins, Martin John; Leach, Ahuroa
Adopting renewable feedstocks is a transformative approach to diminish the reliance on fossil feedstocks such as natural gas and coal in the chemical industry. This research evaluates the potential for Aotearoa-New Zealand, particularly in the North Island, to harness green hydrogen production as a substitute for fossil fuels across industries. The study's scope encompasses examining renewable energy technologies, their capacity factors based on location, types of electrolysers, the conversion process, and the sizing of hydrogen storage reservoirs. An analysis of the levelized cost of hydrogen (LCOH) throughout the value chain in various scenarios has been conducted for the years 2020 to 2040 while considering the country’s resource constraints. The issue is addressed through an optimization-based framework characterized by a multi-period, mixed-integer linear programming (MILP) model. The outcomes demonstrate the capability of integrating all these components within the mathematical framework to yield optimal solutions for transitioning towards a sustainable hydrogen economy.
The role of Adaptive Energy Digital Twin technology in decarbonising emissions in the New Zealand process heat sector
(2023) Walmsley, Michael R.W.
New Zealand (NZ) is uniquely placed to meet the goal of net zero emissions in the industry sector by 2050, but only with an 80% expansion of renewable electricity generation (TWh) combined with energy efficiency improvements through advanced process heat integration, improved energy system design and control, future deployment of high temperature heat pumps (HTHP) for process heat up to 200oC and biomass for heat above 200oC, and smart integration of renewable electricity via microgrid connected factories and communities. The development of Adaptive Energy Digital Twin (AEDT) technology applied widely by energy consultants, equipment providers and factory owners, is considered a key development to aid industry decarbonisation. A seven-year research programme is underway in NZ to develop an open source AEDT technology platform and to demonstrate its usefulness for decarbonising a wide variety of industry sectors, such as dairy, meat, food, wood, paper, metals and chemical processing industries of NZ. Electricity supply and demand differences across the regions of NZ for 2020 and predicted for 2050 are also presented.
Integrating occupancy density into the environmental assessment of residential buildings: Towards embodied impact reduction at both building and urban level
(Elsevier BV, 2025) Christoforatos, Gerasimos; Pickering, Kim L.; Gauss, Christian; Roy, Krishanu; Beg, Mohammad Dalour Hossen
Life Cycle Assessments (LCA) of buildings typically use gross floor area (GFA)-centric functional units, while urban-scale assessments use occupancy-centric ones. This mismatch reflects the dual functions of buildings (providing space and shelter) and can lead to conflicting strategies, where reducing impacts per GFA at the building level may increase impacts per occupant at the urban level. This study compares these assessment approaches and introduces a dual-functional unit approach that evaluates buildings across both functions. Eight detached houses are assessed using LCA across four impact categories and ranked using a multi-criteria decision-making (MCDM) method for each approach. Results show significant variation in rankings among the established approaches, with several buildings having completely opposite outcomes (e.g., ranked 1st in the GFA-centric assessment but 6th in the occupancy-centric assessment), while the proposed approach produces more consistent rankings, representing both functions. Moreover, a scenario-based analysis compares the three assessments to a control (no-assessment) scenario, considering all detached houses built in Aotearoa New Zealand over the past 5 years. The GFA-centric assessment resulted in increased total impacts (mean difference +0.20% across the four impact categories) by promoting larger and less dense buildings (+0.70 m² per occupant), while the occupancy-centric assessment led to mean impact reductions of -1.98%, while significantly reducing the space per occupant by 0.98m². The proposed approach achieved even greater impact reductions (-2.22%) while reducing space by only 0.31m² per occupant. Finally, a correlation with national climate goals was made, showing the approach could achieve 71.65% of the national carbon reduction target.
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.
Combining Hydromorphic and Shape-Shifting Effects for Programmable Passive Actuation in 4D-Printed Biocomposites
(Elsevier BV, 2025) Bachmann, Phil Aron; Pickering, Kim L.; Gauss, Christian
4D printing involves the fabrication of structures that respond dynamically to external stimuli. While various actuation mechanisms have been extensively studied, the integration of multiple actuation effects remains relatively unexplored. This study examines the combined influence of hydromorphic and shape-shifting effects in a biocomposite containing 40 wt% cellulose fibres. The biocomposite was combined with polylactide (PLA) and processed via 3D printing to produce bi-material strips, which were then comprehensively analysed for their material properties and shape-changing behaviour. Upon immersion in water, the biocomposite expanded by 3.2 % perpendicular to the printing direction and exhibited a marked decrease in Young’s modulus with increasing water content. Bi-material strips 1 mm thick displayed pronounced hydromorphic behaviour, achieving maximum curvatures of 0.036 - 0.052 mm-1 depending on the passive-to-active layer thickness ratio. Thicker strips (4 mm) reached 0.012 mm-1 under the same conditions. When both heat and water were applied as external stimuli, the biocomposite and neat PLA layers became simultaneously active, and curvatures of up to 0.057 mm⁻¹ were obtained for 4 mm strips. This curvature surpassed the hydromorphic-only and shape-shifting-only responses by factors of 4.77 and 1.82, respectively. The results demonstrate that integrating water- and heat-induced stimuli increases achievable curvature and accelerates the response, enabling high-curvature deformations even in relatively thick structures. The approach therefore holds promise for applications that demand significant shape transformations without compromising structural integrity.
Heirlooming and shell money beads in the Solomon Islands
(ANU Press, 2024) Szabó, Katherine; Petchey, Fiona
Strings of shell money made up of hundreds, if not thousands, of intensively worked shell beads have featured in the accounts of anthropologists of Melanesia for over a century, and large collections of these strings are to be found in major museum collections around the world. In the Solomon Islands, the tradition of their production continues to this day. Despite new strings still entering circulation, within villages in and around Malaita there are also older strings, either held communally or under tabu. Local wisdom states that some of these are around two hundred years old. The historical and anthropological literature also makes mention of heirloom shell money strings, although how long such strings may be curated and remain active in cultural life has never been quantified. Here, we investigate two large, complex shell money strings from the Solomon Islands, held in the collections of the Museum of Archaeology and Anthropology, University of Cambridge: one from Makira and the other from Nggela. Through direct accelerator mass spectrometry (AMS) radiocarbon dating of individual beads, we establish the restringing and combining of strings of different ages into new strings, as well as the maintenance in use of individual beads for up to two to three hundred years. This demonstrable case of the heirlooming of shell beads has repercussions for archaeology, and the potential cultural longevity of shell valuables such as these should be a consideration in interpretations.
Work-integrated learning as a landscape of practice
(Work-Integrated Learning New Zealand (WILNZ), 2025) Jackson, Denise; Zegwaard, Karsten; Drewery, David
This article proposes that work-integrated learning (WIL) is a Landscape of Practice (LoP) within the wider higher education ecosystem. It applies concepts from the LoP literature to present a new perspective on WIL programs and ecosystems. It further emphasizes that students are central within the WIL LoP, developing knowledge as they traverse individual communities including industry partners, professional accrediting bodies, careers services, academics, curriculum, and support staff connected to WIL. Additionally, the article highlights the role of higher education institutions in addressing tensions of difference between communities comprising the WIL LoP. The article contributes to the literature on WIL and higher education by conceptualizing WIL as a LoP, revealing a new understanding of how various communities support student development through WIL. It also offers higher education institutions practical implications for developing and maintaining student-centered communities of practice that constitute a supportive WIL LoP.
Ancient Borrelia genomes document the evolutionary history of louse-borne relapsing fever
(American Association for the Advancement of Science (AAAS), 2025) Swali, P; Booth, T; Tan, CCS; McCabe, J; Anastasiadou, K; Barrington, C; Borrini, M; Bricking, A; Buckberry, J; Büster, L; Carlin, R; Gilardet, A; Glocke, I; Irish, JD; Kelly, M; King, M; Petchey, Fiona; Peto, J; Silva, M; Speidel, L; Tait, F; Teoaca, A; Valoriani, S; Williams, M; Madgwick, R; Mullan, G; Wilson, L; Cootes, K; Armit, I; Gutierrez, MG; van Dorp, L; Skoglund, P
Several bacterial pathogens have transitioned from tick-borne to louse-borne transmission, which often involves genome reduction and increasing virulence. However, the timing of such transitions remains unclear. We sequenced four ancient Borrelia recurrentis genomes, the agent of louse-borne relapsing fever, dating from 2300 to 600 years ago. We estimated the divergence from its closest tick-borne relative to 6000 to 4000 years ago, which suggests an emergence coinciding with human lifestyle changes such as the advent of wool-based textiles. Pan-genome analysis indicated that much of the evolution characteristic of B. recurrentis had occurred by ~2300 years ago, though further gene turnover, particularly in plasmid partitioning, persisted until ~1000 years ago. Our findings provide a direct genomic chronology of the evolution of this specialized vector-borne pathogen.
Archaeological evidence of an ethnographically documented Australian Aboriginal ritual dated to the last ice age
(Springer Science and Business Media LLC, 2024-08-01) David, B; Mullett, R; Wright, N; Stephenson, B; Ash, J; Fresløv, J; Delannoy, JJ; McDowell, MC; Mialanes, J; Petchey, Fiona; Arnold, LJ; Rogers, AJ; Crouch, J; Green, H; Urwin, C; Matheson, CD
In societies without writing, ethnographically known rituals have rarely been tracked back archaeologically more than a few hundred years. At the invitation of GunaiKurnai Aboriginal Elders, we undertook archaeological excavations at Cloggs Cave in the foothills of the Australian Alps. In GunaiKurnai Country, caves were not used as residential places during the early colonial period (mid-nineteenth century CE), but as secluded retreats for the performance of rituals by Aboriginal medicine men and women known as ‘mulla-mullung’, as documented by ethnographers. Here we report the discovery of buried 11,000- and 12,000-year-old miniature fireplaces with protruding trimmed wooden artefacts made of Casuarina wood smeared with animal or human fat, matching the configuration and contents of GunaiKurnai ritual installations described in nineteenth-century ethnography. These findings represent 500 generations of cultural transmission of an ethnographically documented ritual practice that dates back to the end of the last ice age and that contains Australia’s oldest known wooden artefacts.
The impact of human dispersals and local interactions on the genetic diversity of coastal Papua New Guinea over the past 2,500 years
(Springer Science and Business Media LLC, 2025) Nägele, K; Kinaston, R; Gaffney, D; Walworth, M; Rohrlach, AB; Carlhoff, S; Huang, Y; Ringbauer, H; Bertolini, E; Tromp, M; Radzeviciute, R; Petchey, Fiona; Anson, D; Petchey, P; Stirling, C; Reid, M; Barr, D; Shaw, B; Summerhayes, G; Buckley, H; Posth, C; Powell, A; Krause, J
The inhabitants of New Guinea and its outlying islands have played an important role in the human history of the Pacific region. Nevertheless, the genetic diversity, particularly of pre-colonial communities, is still understudied. Here we present the ancient genomes of 42 individuals from Papua New Guinea (PNG). The ancient genomic results of individuals from Watom Island (Bismarck Archipelago) and the south and northeastern coasts of PNG are contextualized with new (bio-) archaeological data. The individuals’ accelerator mass spectrometry (AMS) dates span 2,500 years of human habitation, and our results demonstrate the influences of different dispersal events on the genetic make-up of ancient PNG communities. The oldest individuals show an unadmixed Papuan-related genetic signature, whereas individuals dating from 2,100 years before present carry varying degrees of an East-Asian-related contribution. These results and the inferred admixture dates suggest a centuries-long delay in genetic mixture with local communities after the arrival of populations with Asian ancestry. Two geographically close communities on the South Coast, AMS dated to within the past 540 years, diverge in their genetic profiles, suggesting differences in their interaction spheres involving groups with distinct ancestries. The inferred split time of these communities around 650 years before present coincides with intensified settlement activity and the emergence of regional trade networks.
Light limitation and water velocity modify the impacts of simulated marine heatwaves on juvenile giant kelp.
(Wiley, 2025) Bunting, Imogen; Bornemann Santamaría, Laura; Yi Kok, Yun; Krieger, Erik; Mullarney, Julia; D'Archino, Roberta; Cornwall, Christopher
Coastal regions are complex habitats, where multiple natural and anthropogenic drivers can interact to affect the survival and growth of marine organisms. The giant kelp Macrocystis pyrifera is sensitive to increasing seawater temperatures and susceptible to marine heatwaves. Light availability and hydrodynamics can also affect the growth, morphology, and resilience of this species. In this experiment, juvenile sporophytes of M. pyrifera from Scorching Bay, Wellington, Aotearoa, New Zealand, a were exposed to a combination of simulated marine heatwaves at one of four different temperatures (20, 22, and 24°C compared to a 16°C control), one of two irradiance levels (shaded: 0.9 mol photons · m−2 · d−1 or ambient: 1.4 mol photons · m−2 · d−1), and one of two flow speeds (5.3 cm · s−1 or 6.1 cm · s−1) in a fully factorial design. Simulated heatwaves lasted for 21 days, with temperatures ramped by 2°C · d−1, followed by a 21-day recovery phase. The heatwave treatments represented severe heatwaves in present day or hypothetical future conditions, whereas the control represented historical average summer sea temperatures in Wellington, and 21 days represented a realistic duration for heatwaves in this region. Temperature was the main driver of negative physiological impacts, with 100% of sporophytes dying within 42 days of exposure to a 24°C heatwave. Sporophytes experienced 44% mortality at 20°C and 81% mortality at 22°C, and growth rates declined significantly with increasing temperature. However, survival rates were modified by light and water velocity, with 56% of sporophytes surviving under a combination of ambient light and fast water velocity, compared with less than 50% under each of the other light-velocity combinations. Light limitation also reduced sporophyte survival, growth rates, and effective quantum yield. Water velocity alone did not significantly affect sporophytes, but flow speeds had interactive effects with temperature and light. The findings of this experiment suggest that M. pyrifera at sites with optimal environmental conditions, including low sediment loads and fast tidal flows, could be more resilient to marine heatwaves, as long as temperatures do not exceed critical thresholds for survival.

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