Science and Engineering Papers

Permanent URI for this collectionhttps://researchcommons.waikato.ac.nz/handle/10289/38

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

Browse

Now showing 1 - 20 of 3422

Genomic signals of local adaptation across climatically heterogenous habitats in an invasive tropical fruit fly (Bactrocera tryoni)
(Springer Science and Business Media LLC, 2024) Parvizi, Elahe; Vaughan, Amy L.; Dhami, Manpreet K.; McGaughran, Angela
Local adaptation plays a key role in the successful establishment of pest populations in new environments by enabling them to tolerate novel biotic and abiotic conditions experienced outside their native range. However, the genomic underpinnings of such adaptive responses remain unclear, especially for agriculturally important pests. We investigated population genomic signatures in the tropical/subtropical Queensland fruit fly, Bactrocera tryoni, which has an expanded range encompassing temperate and arid zones in Australia, and tropical zones in the Pacific Islands. Using reduced representation sequencing data from 28 populations, we detected allele frequency shifts associated with the native/invasive status of populations and identified environmental factors that have likely driven population differentiation. We also determined that precipitation, temperature, and geographic variables explain allelic shifts across the distribution range of B. tryoni. We found spatial heterogeneity in signatures of local adaptation across various climatic conditions in invaded areas. Specifically, disjunct invasive populations in the tropical Pacific Islands and arid zones of Australia were characterised by multiple significantly differentiated single nucleotide polymorphisms (SNPs), some of which were associated with genes with well-understood function in environmental stress (e.g., heat and desiccation) response. However, invasive populations in southeast Australian temperate zones showed higher gene flow with the native range and lacked a strong local adaptive signal. These results suggest that population connectivity with the native range has differentially affected local adaptive patterns in different invasive populations. Overall, our findings provide insights into the evolutionary underpinnings of invasion success of an important horticultural pest in climatically distinct environments.
Current stewardship practices in invasion biology limit the value and secondary use of genomic data
(Wiley, 2023) Vaughan, Amy L.; Parvizi, Elahe; Matheson, Paige; McGaughran, Angela; Dhami, Manpreet K.
Invasive species threaten native biota, putting fragile ecosystems at risk and having a large-scale impact on primary industries. Growing trade networks and the popularity of personal travel make incursions a more frequent risk, one only compounded by global climate change. With increasing publication of whole-genome sequences lies an opportunity for cross-species assessment of invasive potential. However, the degree to which published sequences are accompanied by satisfactory spatiotemporal data is unclear. We assessed the metadata associated with 199 whole-genome assemblies of 89 invasive terrestrial invertebrate species and found that only 38% of these were derived from field-collected samples. Seventy-six assemblies (38%) reported an ‘undescribed’ sample origin and, while further examination of associated literature closed this gap to 23.6%, an absence of spatial data remained for 47 of the total assemblies. Of the 76 assemblies that were ultimately determined to be field-collected, associated metadata relevant for invasion studies was predominantly lacking: only 35% (27 assemblies) provided granular location data, and 33% (n = 25) lacked sufficient collection date information. Our results support recent calls for standardized metadata in genome sequencing data submissions, highlighting the impact of missing metadata on current research in invasion biology (and likely other fields). Notably, large-scale consortia tended to provide the most complete metadata submissions in our analysis—such cross-institutional collaborations can foster a culture of increased adherence to improved metadata submission standards and a standard of metadata stewardship that enables reuse of genomes in invasion science.
How might climate change affect adaptive responses of Polar Arthropods?
(MDPI, 2023) Matheson, Paige; McGaughran, Angela
Climate change is expected to impact the global distribution and diversity of arthropods, with warmer temperatures forcing species to relocate, acclimate, adapt, or go extinct. The Arctic and Antarctic regions are extremely sensitive to climate change and have displayed profound and variable changes over recent decades, including decreases in sea ice extent, greening of tundra, and changes to hydrological and biogeochemical cycles. It is unclear how polar-adapted arthropods will respond to such changes, though many are expected to be at great risk of extinction. Here, we review the adaptive mechanisms that allow polar arthropods to persist in extreme environments and discuss how the effects of climate change at the poles will likely favour non-native species or those with the ability to rapidly evolve and/or acclimate. We find that physiological, behavioural, plastic, and genetic data are limited in scope for polar arthropods and research on adaptive responses to change is scarce. This restricts our ability to predict how they may respond to a warming climate. We call for a greater investment in research that specifically targets the ecology and evolution of these taxa, including genomic and transcriptomic approaches that can evaluate the potential for plastic and evolved environmental responses.
Sedimentary environment controls carbon sequestration potential of unvegetated intertidal estuarine sediments
(American Geophysical Union (AGU), 2025-12) La Croix, Andrew D.
Unvegetated intertidal sediments are increasingly recognized as contributors to coastal carbon storage, yet their organic carbon burial potential remains poorly constrained. This study examines spatial and temporal patterns of carbon accumulation in unvegetated intertidal flats of Ōhiwa Harbor, New Zealand, using surface sediments and three radiocarbon-dated cores spanning up to ∼7,700 yrs. Within the harbor, five distinct sedimentary facies were identified, each displaying unique sediment characteristics and patterns of organic carbon burial. Mud-rich, low-energy facies, including rippled and bioturbated muds, consistently showed higher organic carbon density and burial rates compared to sandy, more dynamic facies. Estimated carbon stocks in the upper meter of sediment range from 44 to 120 t C ha−1, comparable to or exceeding those of many vegetated coastal habitats. Temporal changes in facies distribution driven by estuarine processes and variations in sediment supply led to significant long-term fluctuations in organic carbon burial. These results demonstrate that organic carbon storage in unvegetated intertidal flats is highly heterogeneous and controlled by the persistence of fine-grained depositional environments. A facies-based framework offers a process-driven approach to assessing and managing blue-carbon potential in estuarine systems increasingly altered by climate and land-use change.
Insights into invasive species from whole‐genome resequencing
(Wiley, 2021) North, Henry L.; McGaughran, Angela; Jiggins, Chris
Studies of invasive species can simultaneously inform management strategies and quantify rapid evolution in the wild. The role of genomics in invasion science is increasingly recognised, and the growing availability of reference genomes for invasive species is paving the way for whole-genome resequencing studies in a wide range of systems. Here, we survey the literature to assess the application of whole-genome resequencing data in invasion biology. For some applications, such as the reconstruction of invasion routes in time and space, sequencing the whole genome of many individuals can increase the accuracy of existing methods. In other cases, population genomic approaches such as haplotype analysis can permit entirely new questions to be addressed and new technologies applied. To date whole-genome resequencing has only been used in a handful of invasive systems, but these studies have confirmed the importance of processes such as balancing selection and hybridization in allowing invasive species to reuse existing adaptations and rapidly overcome the challenges of a foreign ecosystem. The use of genomic data does not constitute a paradigm shift per se, but by leveraging new theory, tools, and technologies, population genomics can provide unprecedented insight into basic and applied aspects of invasion science.
Fitness consequences of population bottlenecks in an invasive blowfly
(Wiley, 2024) Croft, Lillian; Matheson, Paige; Butterworth, Nathan J.; McGaughran, Angela
Invasive species often undergo demographic bottlenecks that cause a decrease in genetic diversity and associated reductions in population fitness. Despite this, they manage to thrive in novel environments. Investigating the effects of inbreeding and genetic bottlenecks on population fitness for invasive species is, therefore, key to understanding how they may survive in new environments. We used the blowfly Calliphora vicina (Sciences, Mathématiques et Physique, 1830, 2, 1), which is native to Europe and was introduced to Australia and New Zealand, to examine the effects of genetic diversity on population fitness. We first collected 59 samples from 15 populations across New Zealand and one in Australia, and used 20,501 biallelic SNPs to investigate population genomic diversity, structure and admixture. We then explored the impacts of repeated experimental bottlenecks on population fitness by creating inbred and outbred lines of C. vicina and measuring a variety of fitness traits. In wild-caught samples, we found low overall genetic diversity, signals of genetic admixture and limited (<3%) genetic differentiation between North and South Island populations, with genetic links between the South Island and Australia. Following experimental bottlenecks, we found significant reductions in fitness for inbred lines. However, fitness effects were not felt equally across all phenotypic traits. Moreover, they were not enough to cause population collapse in any experimental line, suggesting that C. vicina (when under relaxed selection, as in laboratory settings) may be able to compensate for population bottlenecks even when highly inbred. Our results demonstrate the value of a tractable experimental system for investigating processes that may facilitate or hamper biological invasion.
Fake webs, real results: Artificial spiderwebs for eDNA collection
(Wiley, 2025-11) McGaughran, Angela; Bird, Starsha; Dhami, Manpreet K.
Environmental DNA (eDNA)-based detection is a valuable biomonitoring tool that is well-developed for water, soil, and scat substrates. Emergent research is focusing on air as a new substrate, including opportunistically collected natural spiderwebs which may have negative impacts on local spider diversity. Here, we design novel artificial spiderwebs and compare their effectiveness with natural spiderwebs and aquatic eDNA approaches for biomonitoring of terrestrial taxa. A total of 33 eDNA samples (18 water, 6 natural spiderwebs, 9 artificial spiderwebs) were collected from a rural property in Palmerston North (Aotearoa New Zealand). Three amplicons (COI, 16S, and ITS) were sequenced for each sample to evaluate the performance of each collection method for detecting invertebrates, vertebrates, and plant/algal taxa. The 16S amplicon performed best in terms of sequencing output and consistency, as well as species accumulation curves, with the COI dataset performing worst for all eDNA collection methods. Alpha diversity varied by amplicon and collection method in both value and consistency among samples, with 16S and ITS retrieving higher diversity for water samples and both artificial and natural webs outperforming water in fungal COI diversity recovery. Ordination plots showed clear differences in sample similarity across biomes, with all three amplicons showing differentiation between water and either web type. However, specialist species were recovered by each of the two web types, with artificial webs consistently recovering more unique diversity than natural webs. Our results suggest that artificial spiderwebs could be a promising new method in the eDNA biomonitoring toolbox, providing biodiversity data that complements water-based collections and, depending on the research question, may serve as a sufficient proxy for natural spiderweb studies.
Winds of change: Charting a pathway to ecosystem monitoring using airborne environmental DNA
(Wiley, 2025) Tulloch, Rachel L.; Adams, Clare I. M.; Barnes, Matthew A.; Clare, Elizabeth L.; van de Ven, Henrik C.; Cridge, Andrew; Encinas-Viso, Francisco; Fernandes, Kristen; Gleeson, Dianne M.; Hill, Erin; Hopkins, Anna J. M.; Kearns, Anna M.; Kroos, Gracie C.; MacDonald, Anna J.; Martoni, Francesco; McGaughran, Angela; McLay, Todd G. B.; Neaves, Linda E.; Nevill, Paul; Pugh, Andrew; Robinson, Kye J.; Roger, Fabian; Steinrucken, Tracey V.; van der Heyde, Mieke; Villacorta-Rath, Cecilia; Vivian, Jenny; Hahn, Erin E.
Airborne environmental DNA (airborne eDNA) analysis leverages the globally ubiquitous medium of air to deliver broad species distribution data and support ecosystem monitoring across diverse environments. As this emerging technology matures, addressing critical challenges and seizing key opportunities will be essential to fully realize its potentially transformative impact. In June 2024, the Southern eDNA Society convened over 100 researchers, industry leaders, and biodiversity management stakeholders in a landmark workshop to evaluate the current state of airborne eDNA research and chart a course for future development. Participants explored opportunities for integrating airborne eDNA into existing monitoring systems, but they unanimously agreed that research must first be applied to improving understanding of airborne eDNA ecology. The workshop emphasized the importance of collaborative engagement with stakeholders—including government agencies, Indigenous communities, and citizen scientists—to ensure practical and ethical implementation. This summary highlights current challenges and actionable recommendations, including improving our understanding of airborne eDNA ecology, harmonizing sampling methodology (e.g., devices, materials, sampling density, duration), identifying and mitigating sources of error, and fostering early, sustained stakeholder collaboration. By addressing these challenges, airborne eDNA analysis can become a transformative tool for biodiversity, biosecurity, and conservation monitoring on a global scale. Its ability to detect diverse taxonomic groups—including fungi, plants, arthropods, microbes, and vertebrates—positions airborne eDNA as a pivotal technology for holistic terrestrial biodiversity assessments that transcend traditional, species-focused monitoring approaches.
Revisiting genetic data stewardship practices in Aotearoa New Zealand: A call to action on integrating Māori data sovereignty
(Wiley, 2025) Dhami, Manpreet K.; Matheson, Paige; Bird, Starsha; Walker, Leilani; Hohaia, Holden; McGaughran, Angela
Genetic data, including environmental DNA (eDNA), are regularly used to monitor escalating biodiversity concerns globally. In Aotearoa New Zealand, biodiversity is unique and cherished—many species are taonga (treasured) and cared for by kaitiaki (guardians with customary responsibilities), specifically mana whenua with custodial rights (Māori; the Indigenous people of New Zealand). Discussions are currently underway regarding the development of a reference DNA barcode database for biodiversity in Aotearoa New Zealand to improve outcomes for biosecurity surveillance and biodiversity assessment. A priority of these discussions is that the database development and eventual implementation accords with Te Tiriti o Waitangi (The Treaty of Waitangi). Here, we evaluate current practices for storing genetic data from samples collected in Aotearoa New Zealand by examining two major public data repositories—the National Centre for Biotechnology Information (NCBI) GenBank and the Barcode of Life Data System (BOLD). We find that current database practices limit opportunities for Māori data sovereignty, with DNA from many taonga species uploaded to public repositories with no associated restrictions or guidelines over use. This is an important finding that will help shape the development of a future DNA reference database for Aotearoa New Zealand that integrates the rights and interests of Indigenous communities.
Whole genome resequencing reveals origins and global invasion pathways of the Japanese beetle Popillia japonica
(Wiley, 2025) Funari, Rebecca; Parvizi, Elahe; Cucini, Claudio; Boschi, Sara; Cardaioli, Elena; Potter, Daniel A.; Asano, Shin-ichiro; Toubarro, Duarte; Jelmini, Luca; Paoli, Francesco; Carapelli, Antonio; McGaughran, Angela; Frati, Francesco; Nardi, Francesco
Invasive species are an increasing global threat given their ability to rapidly spread and adapt to novel environments. The adverse ecological and economic impacts of invasive species highlight the critical need to understand the mechanisms that underpin invasion processes and success. The Japanese beetle, Popillia japonica, is an invasive pest of remarkable interest, as it feeds on hundreds of economically valuable plant species. It has been expanding outside of its native range in Japan since the first decades of the 20th century, colonising large areas of North America and, more recently, Europe. Here, we compared whole-genome resequencing data from individuals encompassing the entire species distribution to study the geographic differentiation of P. japonica populations and reconstruct expansion routes from Japan to the USA and Europe. We found six genomically distinguishable clusters, corresponding to the approximate colonisation areas at a continental scale. Our analysis supported an ancestral divergence between South and North/Central Japan, with the latter being the source of the initial invasion to the USA. Coalescent simulations supported independent bridgehead events from the USA to the Azores and Italy. We also investigated possible signals of selection to better understand the adaptive mechanisms that underlie the invasion success of P. japonica. However, the absence of strong selection signatures suggested that the beetle's adaptive ability might be embedded in pre-existing genomic features. Our comprehensive genome-wide dataset allowed a detailed inference of the invasion process and may be useful in determining the origin of P. japonica individuals in future invasion events.
A landscape genetics approach reveals species-specific connectivity patterns for stream insects in fragmented habitats
(Wiley, 2025) de Araujo Barbosa, Vanessa; Graham, S. Elizabeth; Hogg, Ian D.; Smith, Brian J.; McGaughran, Angela
Dispersal is a critical process in ecology and evolution, shaping global biodiversity patterns. In stream habitats, which often exist within diverse and fragmented landscapes, dispersal ensures population connectivity and survival. For aquatic insects in particular, landscape features may significantly influence the degree of genetic connectivity among populations. Thus, understanding connectivity drivers in such populations is essential for the conservation and management of streams. We conducted a landscape genetic study using mitochondrial DNA (mtDNA) and genome-wide single nucleotide polymorphism (SNP) markers to assess the functional connectivity of stream insects in a fragmented pasture-dominated landscape. We focused on three species with terrestrial winged adults: the mayfly Coloburiscus humeralis, the stonefly Zelandobius confusus, and the caddisfly Hydropsyche fimbriata. We observed significant spatial genetic structure at larger geographical distances (populations separated by ~30 and 170 km). However, the effects of landscape factors, which were assessed at fine spatial scales, varied among species: for C. humeralis SNP data, genetic differentiation was weakly correlated with land cover, suggesting greater population connectivity within stream channels protected by forested riparian zones compared to fragmented streams; for Z. confusus, widespread gene flow indicated high dispersal potential across forested and pasture land; while overland dispersal was reduced for H. fimbriata (potentially due to local habitat features), this did not seem to hinder broader population connectivity. Our results emphasise the importance of assessing landscape features when evaluating population connectivity in stream riparian zones, which can greatly benefit stream management efforts through an enhanced understanding of connectivity dynamics.
Recent developments in work-integrated learning and future directions
(2025) Zegwaard, Karsten E.
This presentation focuses on recent research-informed developments in work-integrated learning (WIL), including both placement and non-placement types of WIL. Resources and examples of good practices will be shared, as well as current trends, future directions, challenges, and opportunities.
The Pacific Archaeology Radiocarbon Database
(Wiley, 2025-07-29) Bickler, Simon; Petchey, Fiona; Bickler, Gideon; Mulrooney, Mara; Rieth, Timothy; Jennings, Richard; Bunbury, Magdalena
This paper describes the Pacific Archaeology Radiocarbon Database (PARD), which includes radiocarbon data from archaeological sites excavated in an area commonly described as Near and Remote Oceania. The collated 14C database is available using ArcGIS Online, an online geospatial system with searchable fields and locational navigation. The online PARD currently has over 17,000 radiocarbon measurements from archaeological sites from over 300 islands in the Pacific. The database contains many inconsistencies reflecting the long history of radiocarbon dating in the Pacific and issues relating to date calculation, precision, contamination removal, in-built age, and contextual uncertainty. While ‘chronometric hygiene’ protocols have demonstrated the reasons for treating such radiocarbon ages with caution, the presence of these data can still provide important information. The location of early excavations, distribution of site types at certain broad time periods, and other such information are useful in providing frameworks for future research. The PARD is a valuable starting point for researchers and communities in the Pacific. It has the potential to assist researchers in coordinating site location data for excavations and promises to aid a more extensive investigation of key research themes. The accessibility of the data online allows stakeholders, particularly indigenous groups across the Pacific, to improve their access to and understanding of the value of archaeological research. Cet article décrit la base de données radiocarbone archéologique du Pacifique (PARD), qui comprend des données radiocarbone provenant de sites archéologiques fouillés en Océanie proche et lointaine. La base de données 14C compilée est accessible via ArcGIS Online. La PARD en ligne contient actuellement plus de 17,000 mesures radiocarbone provenant de sites archéologiques de centaines d'îles du Pacifique La localisation de fouilles la répartition par types de site, grande période et autres fournissent un cadre utile pour de futures recherches. Les données de localisation de sites clés pourraient permettre de réalisation d’études plus approfondies.
AMS radiocarbon dating of Rattus Exulans bone from the Kokohuia Site (New Zealand)
(Oxford University School of Archaeology, 2004) Higham, Thomas F.G.; Ramsey, Christopher Bronk; Petchey, Fiona; Tompkins, C.; Taylor, M.; Higham, Thomas F.G.; Ramsey, Christopher Bronk; Owen, Clare
We AMS radiocarbon dated rat bones (Pacific rat (Rattus exulans)) from the archaeological site of Kokohuia, in Northland, New Zealand. An initial series were up to 1200 years too old, but the reason for the offset remained obscure. We considered dietary foodwebs, post-depositional contamination and taphonomy as possible explanations. None provided robust answers. Finally, we identified a laboratory-related error, in which a small amount of old carbon derived from humectants (glycerin) used to moisten ultrafilters prior to the extraction of bone collagen, had become incorporated in the dated collagen. The glycerin humectant was present in amounts averaging 30-40 mg C per ultrafilter, which ordinarily is too small to significantly affect single dates obtained on bone collagen, but was significant in the case of small rat bones. Redating of bones from identical contexts produced a series of results which were within agreement with the age of the site as determined from other materials, including short-lived identified charcoal, and marine and estuarine shell. These results sound a warning for dating very small bone samples, and emphasise the need to consider all possible contaminants derived from laboratory preparation and chemical processing background. In addition, it emphasises the requirement for utilising standard samples of identical type (eg, bone, charcoal, wood etc) which range from young (1-2 half-lives) to background in age, as well as low and high sample mass, as QA laboratory checks on reproducibility (Bronk Ramsey et al., in press).
Strengthening mechanisms of Ti via Al addition
(Elsevier, 2020) Bolzoni, Leandro; Raynova, Stiliana (Stella) Rousseva; Yang, Fei
Pure Ti is characterised by an interesting combination of performance from an engineering point of view. The addition of Al to Ti can be used to reduce the intrinsic cost of the material, decrease the density of the alloy, and increase the mechanical performance. This study is focused on evaluating the physical properties, microstructural evolution and mechanical behaviour of Ti-xAl alloys (where x = 1–6 wt%) in order to scientifically understand the strengthening mechanisms of the addition of Al to pure Ti manufactured via the conventional powder metallurgy route of cold uniaxial pressing plus solid state sintering. The addition of Al to Ti does not affect the compressibility of the alloy but changes the consolidation and densification of the alloy. The incremental addition of Al results in the progressive strengthening of Ti via the simultaneous contribution from substitutional solid solution and grain refinement strengthening which outdo the negative effect of the residual porosity.
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.

Browse

Recent Submissions