10,436 results for ResearchCommons@Waikato

  • A spatially resolved model of seasonal variations in phytoplankton and clam (Tapes philippinarum) biomass in Barbamarco Lagoon, Italy

    Spillman, C.M.; Hamilton, David P.; Hipsey, Matthew R.; Imberger, J. (2011)

    Journal article
    University of Waikato

    Barbamarco Lagoon (area = 7 km²) is in the Po River Delta, adjoining the Northern Adriatic Sea, and supports a commercially valuable clam (Tapes philippinarum) fishery. This study investigated interactions of the lagoon with adjacent coastal waters and inland riverine inputs by modelling both the lagoon and the Northern Adriatic Sea, using a coupled three-dimensional (3D) hydrodynamic-ecological model (ELCOM-CAEDYM) adapted to include the clam population. The clam model accounted for carbon (C), nitrogen (N) and phosphorus (P) biomass in the benthos through parameterisations for filtration, excretion, egestion, respiration, mortality, and harvesting. Multiple clam size classes were included in a new population dynamics sub-model. Output from the coupled model was validated against hydrodynamic and water quality data from intensive field sampling and routine monitoring. Time scales of tidal flushing, primary production and clam grazing were investigated with the model to demonstrate that food supply to clam populations is dominated by phytoplankton inputs from the Northern Adriatic Sea. Effects of clam cultivation on nutrient concentrations and phytoplankton biomass in Barbamarco Lagoon were primarily localised, with strong tidal flushing minimising impacts of clam filtration on lagoon-wide nutrient concentrations at current clam stocking levels. Clam populations were found to alter the cycling of nutrients in the system, causing the lagoon to become a net sink for particulate organic matter and to export dissolved organic matter to the adjacent sea via tidal flushing. Ecosystem health and sensitivity of nutrient cycles to clam cultivation are important considerations for the long term sustainable management and potential expansion of the fishery.

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  • Eco-physiological adaptations that favour freshwater cyanobacteria in a changing climate

    Carey, Cayelan C.; Ibelings, Bas W.; Hoffmann, Emily P.; Hamilton, David P.; Brookes, Justin D. (2012-04)

    Journal article
    University of Waikato

    Climate change scenarios predict that rivers, lakes, and reservoirs will experience increased temperatures, more intense and longer periods of thermal stratification, modified hydrology, and altered nutrient loading. These environmental drivers will have substantial effects on freshwater phytoplankton species composition and biomass, potentially favouring cyanobacteria over other phytoplankton. In this Review, we examine how several cyanobacterial eco-physiological traits, specifically, the ability to grow in warmer temperatures; buoyancy; high affinity for, and ability to store, phosphorus; nitrogen-fixation; akinete production; and efficient light harvesting, vary amongst cyanobacteria genera and may enable them to dominate in future climate scenarios. We predict that spatial variation in climate change will interact with physiological variation in cyanobacteria to create differences in the dominant cyanobacterial taxa among regions. Finally, we suggest that physiological traits specific to different cyanobacterial taxa may favour certain taxa over others in different regions, but overall, cyanobacteria as a group are likely to increase in most regions in the future.

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  • Feed-forward mechanisms: Addiction-like behavioral and molecular adaptations in overeating

    Alsiö, Johan; Olszewski, Pawel K.; Levine, Allen S.; Schiöth, Helgi B. (2012)

    Journal article
    University of Waikato

    Food reward, not hunger, is the main driving force behind eating in the modern obesogenic environment. Palatable foods, generally calorie-dense and rich in sugar/fat, are thus readily overconsumed despite the resulting health consequences. Important advances have been made to explain mechanisms underlying excessive consumption as an immediate response to presentation of rewarding tastants. However, our understanding of long-term neural adaptations to food reward that oftentimes persist during even a prolonged absence of palatable food and contribute to the reinstatement of compulsive overeating of high-fat high-sugar diets, is much more limited. Here we discuss the evidence from animal and human studies for neural and molecular adaptations in both homeostatic and non-homeostatic appetite regulation that may underlie the formation of a “feed-forward” system, sensitive to palatable food and propelling the individual from a basic preference for palatable diets to food craving and compulsive, addiction-like eating behavior.

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  • Time-scale dependence in numerical simulations: Assessment of physical, chemical, and biological predictions in a stratified lake at temporal scales of hours to months

    Kara, Emily L.; Hanson, Paul C.; Hamilton, David P.; Hipsey, Matthew R.; McMahon, Katherine D.; Read, Jordan S.; Winslow, Luke A.; Dedrick, John; Rose, Kevin; Carey, Cayelan C.; Bertilsson, Stefan; da Motta Marques, David; Beversdorf, Lucas; Miller, Todd; Wu, Chin H.; Hsieh, Yi-Fang; Gaiser, Evelyn; Kratz, Tim (2012-07)

    Journal article
    University of Waikato

    We evaluated the predictive ability of a one-dimensional coupled hydrodynamic-biogeochemical model across multiple temporal scales using wavelet analysis and traditional goodness-of-fit metrics. High-frequency in situ automated sensor data and long-term manual observational data from Lake Mendota, Wisconsin, USA, were used to parameterize, calibrate, and evaluate model predictions. We focused specifically on short-term predictions of temperature, dissolved oxygen, and phytoplankton biomass over one season. Traditional goodness-of-fit metrics indicated more accurate prediction of physics than chemical or biological variables in the time domain. This was confirmed by wavelet analysis in both the time and frequency domains. For temperature, predicted and observed global wavelet spectra were closely related, while observed dissolved oxygen and chlorophyll fluorescence spectral characteristics were not reproduced by the model for key time scales, indicating that processes not modeled may be important drivers of the observed signal. Although the magnitude and timing of physical and biological changes were simulated adequately at the seasonal time scale through calibration, time scale-specific dynamics, for example short-term cycles, were difficult to reproduce, and were relatively insensitive to the effects of varying parameters. The use of wavelet analysis is novel to aquatic ecosystem modeling, is complementary to traditional goodness-of-fit metrics, and allows for assessment of variability at specific temporal scales. In this way, the effect of processes operating at distinct temporal scales can be isolated and better understood, both in situ and in silico. Wavelet transforms are particularly well suited for assessment of temporal and spatial heterogeneity when coupled to high-frequency data from automated in situ or remote sensing platforms.

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  • Temperature-related changes in polar cyanobacterial mat diversity and toxin production

    Kleinteich, Julia; Wood, Susanna A.; Küpper, Frithjof C.; Camacho, Antonio; Quesada, Antonio; Frickey, Tancred; Dietrich, Daniel R. (2012)

    Journal article
    University of Waikato

    One of the fastest rates of recent climate warming has been reported for the Arctic and the maritime Antarctic; for example, mean annual temperatures increased by 0.5 °C per decade over the Antarctic Peninsula during the past 50 years. Owing to their comparatively simple and highly sensitive food webs, polar freshwater systems, with cyanobacterial mats representing the dominant benthic primary producers, seem well suited for monitoring environmental perturbation, including climate change. Prolonged climate change may challenge the resilience, plasticity and adaptability and thus affect the community composition of cyanobacterial mats. We demonstrate that exposing polar mat samples to raised temperatures for six months results in a change in species predominance. Mats exposed to a constant temperature of 8 °C or 16 °C showed high cyanobacterial diversity, commensurate with an increased presence of cyanobacterial toxins. In contrast, mats held at 4 °C and 23 °C seemed low in diversity. Our data thus indicate that a temperature shift to 8–16 °C, potentially reached during summer months in polar regions at the present warming rate, could affect cyanobacterial diversity, and in some instances result in a shift to toxin-producing species or to elevated toxin concentrations by pre-existing species that could profoundly alter freshwater polar ecosystems.

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  • A community-based framework for aquatic ecosystem models

    Trolle, Dennis; Hamilton, David P.; Hipsey, Matthew R.; Bolding, Karsten; Bruggeman, Jorn; Mooij, Wolf M.; Janse, Jan H.; Nielsen, Anders; Jeppesen, Erik; Elliott, J. Alex; Makler-Pick, Vardit; Petzoldt, Thomas; Rinke, Karsten; Flindt, Mogens R.; Arhonditsis, George B.; Gal, Gideon; Bjerring, Rikke; Tominaga, Koji; Hoen, Jochem't; Downing, Andrea S.; Marques, David M.; Fragoso, Carlos R.; Søndergaard, Martin; Hanson, Paul C. (2011)

    Journal article
    University of Waikato

    Here, we communicate a point of departure in the development of aquatic ecosystem models, namely a new community-based framework, which supports an enhanced and transparent union between the collective expertise that exists in the communities of traditional ecologists and model developers. Through a literature survey, we document the growing importance of numerical aquatic ecosystem models while also noting the difficulties, up until now, of the aquatic scientific community to make significant advances in these models during the past two decades. Through a common forum for aquatic ecosystem modellers we aim to (i) advance collaboration within the aquatic ecosystem modelling community, (ii) enable increased use of models for research, policy and ecosystem-based management, (iii) facilitate a collective framework using common (standardised) code to ensure that model development is incremental, (iv) increase the transparency of model structure, assumptions and techniques, (v) achieve a greater understanding of aquatic ecosystem functioning, (vi) increase the reliability of predictions by aquatic ecosystem models, (vii) stimulate model inter-comparisons including differing model approaches, and (viii) avoid ‘re-inventing the wheel’, thus accelerating improvements to aquatic ecosystem models. We intend to achieve this as a community that fosters interactions amongst ecologists and model developers. Further, we outline scientific topics recently articulated by the scientific community, which lend themselves well to being addressed by integrative modelling approaches and serve to motivate the progress and implementation of an open source model framework.

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  • Incidence of traumatic brain injury in New Zealand: A population-based study

    Feigin, Valery L.; Theadom, Alice; Barker-Collo, Suzanne; Starkey, Nicola J.; McPherson, Kathryn; Kahan, Michael; Dowell, Anthony; Brown, Paul; Parag, Varsha; Kydd, Robert; Jones, Kelly; Jones, Amy; Ameratunga, Shanthi (2013)

    Journal article
    University of Waikato

    Background Traumatic brain injury (TBI) is the leading cause of long-term disability in children and young adults worldwide. However, accurate information about its incidence does not exist. We aimed to estimate the burden of TBI in rural and urban populations in New Zealand across all ages and TBI severities. Methods We did a population-based incidence study in an urban (Hamilton) and rural (Waikato District) population in New Zealand. We registered all cases of TB! (admitted to hospital or not, fatal or non-fatal) that occurred in the population between March 1, 2010, and Feb 28, 2011, using multiple overlapping sources of information. We calculated incidence per 100 000 person-years with 95% CIs using a Poisson distribution. We calculated rate ratios [RRs] to compare the age-standardised rates between sex, ethnicity, and residency (urban, rural) groups. We used direct standardisation to age-standardise the rates to the world population. Results The total incidence of TBI per 100 000 person-years was 790 cases (95% CI 749-832); incidence per 100 000 person-years of mild TBI was 749 cases (709-790) and of moderate to severe TBI was 41 cases (31-51). Children (aged 0-14 years) and adolescents and young adults (aged 15-34 years) constituted almost 70% of all TBI cases. TBI affected boys and men more than women and girls (RR 1.77,95% CI 1.58-1.97). Most TBI cases were due to falls (38% [516 of 1369]), mechanical forces (21% [288 of 1369]), transport accidents (20% [277 of 1369]), and assaults (17% [228 of 1369]). Compared with people of European origin, Maori people had a greater risk of mild TBI (RR 1.23, 95% CI 1.08-1.39). Incidence of moderate to severe TBI in the rural population (73 per 100 000 person-years [95% CI 50-107]) was almost 2.5 times greater than in the urban population (31 per 100 000 person-years [23-42]). Interpretation Our findings suggest that the incidence of TBI, especially mild TBI, in New Zealand is far greater than would be estimated from the findings of previous studies done in other high-income countries. Our age-specific and residency-specific data for TBI incidence overall and by mechanism of injury should be considered when planning prevention and TBI care services.

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  • Latitudinal variation in nutrient stoichiometry and chlorophyll-nutrient relationships in lakes: A global study

    Abell, Jonathan Michael; Özkundakci, Deniz; Hamilton, David P.; Jones, John R. (2012)

    Journal article
    University of Waikato

    We present analysis of variations in relationships between nitrogen (N), phosphorus (P) and chlorophyll-a (chl-a) in lakes along a gradient of latitude inclusive of tropical, temperate and polar regions. Total nitrogen (TN), total phosphorus (TP), chl-a, latitude and depth data were collated for 1316 lakes situated between 70 degrees S and 83 N. Latitudinal variation was then analysed for three empirical measures of phytoplankton nutrient limitation and/or nutrient assimilation. Lastly, chl-a near-maxima conditional on TN and TP abundance were empirically defined for this global dataset using quantile regression. Mean TN:TP increases with distance from the equator. This relationship is independent of variation in either lake depth or trophic state, reflecting latitudinal variation in nutrient cycling processes and/or nutrient sources. There is a negative linear relationship between latitude and chl-a:TN which similarly suggests that N is less abundant relative to phytoplankton growth requirements at lower latitudes. Relative to temperate lakes, the statistical capability of TN and TP to predict chl-a is poor for both tropical and polar lakes, reflecting latitudinal variation in lake ecosystem functioning and the subsequent potential unsuitability of applying relationships derived for temperate lakes elsewhere. Chl-a near-maxima correspond to chl-a:TN and chl-a:TP yields of 0.046:1 and 0.87:1 respectively, although some observations greatly exceed near-maxima, suggesting possible physiologically plastic phytoplankton responses in these exceptional cases. Deficiencies in understanding the mechanisms that drive variation in macro-nutrient stoichiometry and phytoplankton biomass-nutrient relationships across large spatial scales necessitates further landscape-scale research on this topic, particularly in the tropics.

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  • The telegraph equation for cosmic-ray transport with weak adiabatic focusing

    Litvinenko, Yuri E.; Schlickeiser, Reinhard (2013)

    Journal article
    University of Waikato

    Time-dependent solutions of a spatial diffusion equation are often used to describe the transport of solar energetic particles, accelerated in large solar flares. Approximate analytical solutions of the diffusion approximation can complement and guide detailed numerical solutions of the Fokker-Planck equation for the particle distribution function. The accuracy of the diffusion approximation is limited, however, because the signal propagation speed is infinite in the diffusion limit. An improved description of cosmic-ray transport is provided by the telegraph equation, characterised by a finite signal propagation speed. We derive the telegraph equation for the particle density, taking into account adiabatic focusing in a large-scale interplanetary magnetic field in a weak focusing limit. As an illustration, we calculate a propagating pulse solution of the telegraph equation, determine the rise time when the maximum particle intensity is reached at a given distance from the Sun, and compare the results with those obtained in the diffusion approximation. In comparison with the diffusion equation, the telegraph equation predicts an asymmetrical shape of the pulse and a shorter rise time. These potentially significant differences suggest that the more accurate telegraph equation should be used in analysis of the solar energetic particle data, at least to quantify the accuracy of the focused diffusion model.

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  • A bi-objective model for supply chain design of dispersed manufacturing in China

    Zhang, Abraham; Luo, Hao; Huang, George Q. (2013)

    Journal article
    University of Waikato

    Dispersed manufacturing achieves the greatest cumulative competitive advantage by dissecting a supply chain and assigning each process to an optimal location. Dispersed manufacturing has been an integral part of global manufacturing in China. This paper presents a bi-objective model for the supply chain design of dispersed manufacturing in the context of rising business operating costs in coastal China. It considers essential trade-offs between supply chain cost and lead time to determine optimal facility locations of manufacturing steps. The model is applied to a representative case to illustrate the cost benefits of dispersed manufacturing as opposed to performing all manufacturing steps of a product at a single facility location. It provides explanations in several factors that have benefited manufacturing growth in China, and offers insights in the emerging global manufacturing trends.

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  • Potential science tools to support mahinga kai decision-making in freshwater management

    Collier, Kevin J.; Death, Russell G.; Hamilton, David P.; Quinn, John M. (2014)

    Report
    University of Waikato

    Mahinga kai is a key value for freshwater management that needs to be articulated in objective setting for environmental limits in the National Objectives Framework (NOF). Mahinga kai generally refers to indigenous freshwater species that have traditionally been used for food, tools or other resources. Many mahinga kai sites, both current and historical, are in lowland settings where freshwater environments are often in a degraded state and values are correspondingly compromised. With limited availability of sites in good condition within rohe to help define desired states for mahinga kai, alternative approaches are needed to establish condition bands for management. In particular, tools that assist with envisaging desired states and predicting environmental changes required to sustain those states will help communities and tangata whenua set management objectives. To achieve this effectively an approach is required that utilises Mātauranga Māori and science tools

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  • Use of high-intensity data to define large river management units: A case study on the lower Waikato River, New Zealand

    Pingram, Michael Alister; Collier, Kevin J.; Hamilton, David P.; David, Bruno O.; Hicks, Brendan J. (2014)

    Journal article
    University of Waikato

    The importance of environmental heterogeneity in lotic ecosystems is well recognised in river management, and continues to underpin studies of hierarchical patch dynamics, geomorphology and landscape ecology. We evaluated how physical characteristics and water chemistry measurements at high spatiotemporal resolution define channel units of potential ecological importance along 134 km of the lower Waikato River in North Island, New Zealand. We used multivariate hierarchical clustering to classify river reaches in an a priori unstructured manner based on (i) high-frequency, along-river water quality measurements collected in four seasons and (ii) river channel morphology data resolved from aerial photos for 1-km long reaches. Patterns of channel character were shaped by the depth and lateral complexity of constituent river reaches, while water quality patterns were represented by differences in clarity, chlorophyll fluorescence and specific conductance driven by tributary inflows in the mid-section of the river and tidal cycles in the lower section. Management units defined by physical characteristics or water quality did not necessarily align with boundaries typically reflecting clinal processes (e.g. tidal influence) or geomorphic, network or anthropogenic discontinuities. The results highlight the dynamic spatial and temporal properties of large rivers and the need to define clear objectives when deriving spatial units for management and research. Given that actions and targets for physical channel and water quality management may differ, the spatial extent identified for each of these does not necessarily need to directly coincide, although both should be considered in decision making and experimental design.

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  • Ua tafea le tau'ofe: Samoan cultural rituals through death and bereavement experiences

    Seiuli, Byron Malaela Sotiata (2015)

    Doctoral thesis
    University of Waikato

    Given that dialogue relating to death and grief for many Samoans remains in the realm of tapu (sacred) or sā (protected), few attempts have been made by researchers of Samoan heritage to understand whether the cultural contexts for enacting associated rituals might also provide avenues for healing. Psychological scholarship on recovery following death, particularly among men, is largely based on dominant western perspectives that continue to privilege both clinical and ethnocentric perspectives as the norm. Using the Samoan experience, I argue for a greater consideration of recovery from death as a culturally-defined process. In many instances, instead of severing ties with the deceased person as is popular in clinical approaches to grief work, this thesis makes an original contribution to the canon by demonstrating that Samoan grief resolution strongly endorses continued connections through its mourning rituals. Their end-of-life enactment helps to transition the deceased from this life to the next, while drawing the living together. Critically, the performance and maintenance of such important tasks create space for heaving emotions to be calmed, where meaning is made, and where the lives of those impacted are slowly restored. Some rituals offered therapeutic value, enabling the Samoan men involved in this study to walk hand-in-hand with their emotional distress, while transitioning them through the grieving process. Such mourning traditions are meaningful and culturally preferred. Moreover, the theoretical framework engaged by this research is predominantly informed by Samoan and Pasefika research perspectives such as the Uputāua Therapeutic Approach (UTA). UTA is firmly grounded in fa’asamoa (Samoan way) cultural traditions, while allowing space for western perspectives of therapeutic care to be incorporated into the research processes. This thesis critically advocates that psychology as a discipline could become more responsive and effective towards considering the centrality of indigenous perspectives of grief resolution when engaging with people from non-western cultures. As this thesis demonstrates, Samoan mourning rituals provided a significant pathway for my participants to validate and celebrate their cultural identity wherever they were situated.

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  • A Global lake ecological observatory network (GLEON) for synthesising high-frequency sensor data for validation of deterministic ecological models

    Hamilton, David P.; Carey, Cayelan C.; Arvola, Lauri; Arzberger, Peter; Brewer, Carol; Cole, Jon J.; Gaiser, Evelyn; Hanson, Paul C.; Ibelings, Bas W.; Jennings, Eleanor; Kratz, Tim K.; Lin, Fang-Pang; McBride, Christopher G.; Marques, David de Motta; Muraoka, Kohji; Nishri, Ami; Qin, Boqiang; Read, Jordan S.; Rose, Kevin C.; Ryder, Elizabeth; Weathers, Kethleen C.; Zhu, Guangwei; Trolle, Dennis; Brookes, Justin D. (2015)

    Journal article
    University of Waikato

    A Global Lake Ecological Observatory Network (GLEON; www.gleon.org) has formed to provide a coordinated response to the need for scientific understanding of lake processes, utilising technological advances available from autonomous sensors. The organisation embraces a grassroots approach to engage researchers from varying disciplines, sites spanning geographic and ecological gradients, and novel sensor and cyberinfrastructure to synthesise high-frequency lake data at scales ranging from local to global. The high-frequency data provide a platform to rigorously validate processbased ecological models because model simulation time steps are better aligned with sensor measurements than with lower-frequency, manual samples. Two case studies from Trout Bog, Wisconsin, USA, and Lake Rotoehu, North Island, New Zealand, are presented to demonstrate that in the past, ecological model outputs (e.g., temperature, chlorophyll) have been relatively poorly validated based on a limited number of directly comparable measurements, both in time and space. The case studies demonstrate some of the difficulties of mapping sensor measurements directly to model state variable outputs as well as the opportunities to use deviations between sensor measurements and model simulations to better inform process understanding. Well-validated ecological models provide a mechanism to extrapolate high-frequency sensor data in space and time, thereby potentially creating a fully 3-dimensional simulation of key variables of interest.

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  • Determining the probability of cyanobacterial blooms: the application of Bayesian networks in multiple lake systems

    Rigosi, Anna; Hanson, Paul; Hamilton, David P.; Hipsey, Matthew; Rusak, James A.; Bois, Julie; Sparber, Karin; Chorus, Ingrid; Watkinson, Andrew J.; Qin, Boqiang; Kim, Bomchul; Brookes, Justin D. (2015-01-01)

    Journal article
    University of Waikato

    A Bayesian network model was developed to assess the combined influence of nutrient conditions and climate on the occurrence of cyanobacterial blooms within lakes of diverse hydrology and nutrient supply. Physicochemical, biological, and meteorological observations were collated from 20 lakes located at different latitudes and characterized by a range of sizes and trophic states. Using these data, we built a Bayesian network to (1) analyze the sensitivity of cyanobacterial bloom development to different environmental factors and (2) determine the probability that cyanobacterial blooms would occur. Blooms were classified in three categories of hazard (low, moderate, and high) based on cell abundances. The most important factors determining cyanobacterial bloom occurrence were water temperature, nutrient availability, and the ratio of mixing depth to euphotic depth. The probability of cyanobacterial blooms was evaluated under different combinations of total phosphorus and water temperature. The Bayesian network was then applied to quantify the probability of blooms under a future climate warming scenario. The probability of the "high hazardous" category of cyanobacterial blooms increased 5% in response to either an increase in water temperature of 0.8°C (initial water temperature above 24°C) or an increase in total phosphorus from 0.01 mg/L to 0.02 mg/L. Mesotrophic lakes were particularly vulnerable to warming. Reducing nutrient concentrations counteracts the increased cyanobacterial risk associated with higher temperatures.

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  • Fia Ola: Grief recovery following a tsunami disaster in Samoa

    Seiuli, Byron Malaela Sotiata; Nikora, Linda Waimarie; Te Awekotuku, Ngahuia; Hodgetts, Darrin (2016)

    Journal article
    University of Waikato

    Natural disasters provide humanity with a setting in which to examine core dimensions of life. How people respond to and make sense of their experiences due to the ruptures of trauma and devastation remains vital in grief recovery. An earthquake of 8.3 magnitudes on 29 October 2009 triggered a galulolo (tsunami wave) that devastated parts of Samoa, American Samoa and Tonga. This calamity provided an ideal setting for a case study examination of how those directly impacted recovered from the devastation. In this article, the experiences of one couple in the context of Samoan grieving processes becomes the key focus. Disaster and grieving literature is examined to inform and provide interpretation to their experiences. It is through such an examination that this article seeks to makes an important contribution to understanding the complexities of loss and culturally patterned responses of Samoan people, like this couple, to disaster recovery.

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  • A global database of lake surface temperatures collected by in situ and satellite methods from 1985–2009

    Sharma, S; Gray, DK; Read, JS; O’Reilly, CM; Schneider, P; Qudrat, A; Gries, C; Stefanoff, S; Hampton, SE; Hook, S; Lenters, JD; Livingstone, DM; McIntyre, PB; Adrian, R; Allan, Mathew Grant; Anneville, O; Arvola, L; Austin, J; Bailey, J; Baron, JS; Brookes, J; Chen, Y; Daly, R; Dokulil, M; Dong, B; Ewing, K; de Eyto, Elvira; Hamilton, David P.; Havens, K; Haydon, S; Hetzenauer, H; Heneberry, J; Hetherington, AL; Higgins, SN; Hixson, E; Izmest’eva, LR; Jones, BM; Kangur, K; Kasprzak, P; Köster, O; Kraemer, BM; Kumagai, M; Kuusisto, E; Leshkevich, G; May, L; MacIntyre, S; Müller-Navarra, D; Naumenko, M; Noges, P; Noges, T; Niederhauser, P; North, RP; Paterson, AM; Plisnier, P-D; Rigosi, A; Rimmer, A; Rogora, M; Rudstam, L; Rusak, JA; Salmaso, N; Samal, NR; Schindler, DE; Schladow, G; Schmidt, SR; Schultz, T; Silow, EA; Straile, D; Teubner, K; Verburg, P; Voutilainen, A; Watkinson, A; Weyhenmeyer, GA; Williamson, CE; Woo, KH (2015-03-17)

    Journal article
    University of Waikato

    Global environmental change has influenced lake surface temperatures, a key driver of ecosystem structure and function. Recent studies have suggested significant warming of water temperatures in individual lakes across many different regions around the world. However, the spatial and temporal coherence associated with the magnitude of these trends remains unclear. Thus, a global data set of water temperature is required to understand and synthesize global, long-term trends in surface water temperatures of inland bodies of water. We assembled a database of summer lake surface temperatures for 291 lakes collected in situ and/or by satellites for the period 1985–2009. In addition, corresponding climatic drivers (air temperatures, solar radiation, and cloud cover) and geomorphometric characteristics (latitude, longitude, elevation, lake surface area, maximum depth, mean depth, and volume) that influence lake surface temperatures were compiled for each lake. This unique dataset offers an invaluable baseline perspective on global-scale lake thermal conditions as environmental change continues.

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  • The effect of cyanobacterial biomass enrichment by centrifugation and GF/C filtration on subsequent microcystin measurement

    Rogers, Shelley; Puddick, Jonathan; Wood, Susanna A.; Dietrich, Daniel R.; Hamilton, David P.; Prinsep, Michèle R. (2015-03)

    Journal article
    University of Waikato

    Microcystins are cyclic peptides produced by multiple cyanobacterial genera. After accumulation in the liver of animals they inhibit eukaryotic serine/threonine protein phosphatases, causing liver disease or death. Accurate detection/quantification of microcystins is essential to ensure safe water resources and to enable research on this toxin. Previous methodological comparisons have focused on detection and extraction techniques, but have not investigated the commonly used biomass enrichment steps. These enrichment steps could modulate toxin production as recent studies have demonstrated that high cyanobacterial cell densities cause increased microcystin levels. In this study, three microcystin-producing strains were processed using no cell enrichment steps (by direct freezing at three temperatures) and with biomass enrichment (by centrifugation or GF/C filtration). After extraction, microcystins were analyzed using liquid chromatography-tandem mass spectrometry. All processing methods tested, except GF/C filtration, resulted in comparable microcystin quotas for all strains. The low yields observed for the filtration samples were caused by adsorption of arginine-containing microcystins to the GF/C filters. Whilst biomass enrichment did not affect microcystin metabolism over the time-frame of normal sample processing, problems associated with GF/C filtration were identified. The most widely applicable processing method was direct freezing of samples as it could be utilized in both field and laboratory environments.

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  • Modelling water, sediment and nutrient fluxes from a mixed land-use catchment in New Zealand: effects of hydrologic conditions on SWAT model performance

    Me, W.; Abell, Jonathan Michael; Hamilton, David P. (2015-04-29)

    Journal article
    University of Waikato

    The Soil Water Assessment Tool (SWAT) was configured for the Puarenga Stream catchment (77 km2), Rotorua, New Zealand. The catchment land use is mostly plantation forest, some of which is spray-irrigated with treated wastewater. A Sequential Uncertainty Fitting (SUFI-2) procedure was used to auto-calibrate unknown parameter values in the SWAT model which was applied to the Puarenga catchment. Discharge, sediment, and nutrient variables were then partitioned into two components (base flow and quick flow) based on hydrograph separation. A manual procedure (one-at a-time sensitivity analysis) was then used to quantify parameter sensitivity for the two hydrologically-separated regimes. Comparison of simulated daily mean discharge, sediment and nutrient concentrations with high-frequency, event-based measurements allowed the error in model predictions to be quantified. This comparison highlighted the potential for model error associated with quick-flow fluxes in flashy lower-order streams to be underestimated compared with low-frequency (e.g. monthly) measurements derived predominantly from base flow measurements. To overcome this problem we advocate the use of high-frequency, event-based monitoring data during calibration and dynamic parameter values with some dependence on discharge regime. This study has important implications for quantifying uncertainty in hydrological models, particularly for studies where model simulations are used to simulate responses of stream discharge and composition to changes in irrigation and land management.

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  • Action on the ground: A review of community environmental groups’ restoration objectives, activities and partnerships in New Zealand

    Peters, Monica A.; Hamilton, David P.; Eames, Chris W. (2015)

    Journal article
    University of Waikato

    More than 600 community environmental groups across New Zealand are engaged in restoring degraded sites and improving and protecting habitat for native species. In the face of ongoing biodiversity declines, resource management agencies are increasing their reliance on these groups to enhance conservation outcomes nationally. However, little is known about community groups and their activities beyond local or regional studies. Our aim was to develop a profile of community groups and their projects through examining group and project characteristics, objectives, activities and the support provided by project partners. A total of 296 community groups from all mainland regions of New Zealand responded to an online questionnaire. Nearly 80% of these groups were established for ≥6 years and 72% operated with ≤20 participants (e.g. staff, members, and unpaid volunteers). For over half (54%) of groups, participants were mostly aged 51–65 years. Small groupsizes, combined with ageing participants, may threaten groups’ longevity. More than 20% of groups’ projects covered areas > 501 ha. Ecosystems represented within groups’ project areas included forests (64.0%), streams (42.0%) and freshwater wetlands (33.2%). Over one-third (37.2%) of freshwater wetland restoration projects occurred on private or Maori-owned land. Nearly 70% of groups carried out weed/pest control, native tree planting and advocacy/educational activities, underscoring the combination of social and ecological dimensions shaping most groups’ projects. Over 90% of groups were supported by project partners (e.g. resource management agencies for site visits, funding and technical support), highlighting the interdependence between groups and their partners. Developing a more complete profile of New Zealand community groups and their projects will assist with improving the delivery of support to groups by project partners and developing an inclusive and cohesive sector based on meaningful partnerships. These two factors combined will ultimately enhance groups’ environmental outcomes at the local level, while contributing to national biodiversity conservation goals.

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