200 results for Lowe, David J.

  • Two-step human−environmental impact history for northern New Zealand linked to late-Holocene climate change

    Newnham, Rewi M.; Lowe, David J.; Gehrels, Maria J.; Augustinus, Paul Christian (2018)

    Journal article
    University of Waikato

    Following resolution of a long-standing debate over the timing of the initial settlement of New Zealand from Polynesia (late 13th century), a prevailing paradigm has developed that invokes rapid transformation of the landscape, principally by fire, within a few decades of the first arrivals. This model has been constructed from evidence mostly from southern and eastern regions of New Zealand, but a more complicated pattern may apply in the more humid western and northern regions where forests are more resilient to burning. We present a new pollen record from Lake Pupuke, Auckland, northern New Zealand, that charts the changing vegetation cover over the last 1000 years, before and after the arrival of people. Previous results from this site concurred with the rapid transformation model, although sampling resolution, chronology and sediment disturbance make that interpretation equivocal. Our new record is dated principally by tephrochronology together with radiocarbon dating, and includes a cryptotephra deposit identified as Kaharoa tephra, a key marker for first settlement in northern New Zealand. Its discovery and stratigraphic position below two Rangitoto-derived tephras enables a clearer picture of environmental change to be drawn. The new pollen record shows an early phase (step 1) of minor, localised forest clearance around the time of Kaharoa tephra (c. 1314 AD) followed by a later, more extensive deforestation phase (step 2) commencing at around the time of deposition of the Rangitoto tephras (c. 1400‒1450 AD). This pattern, which needs to be corroborated from other well-resolved records from northern New Zealand, concurs with an emerging hypothesis that the ‘Little Ice Age’ had a significant impact on pre-European Māori with the onset of harsher conditions causing a consolidation of populations and later environmental impact in northern New Zealand.

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  • "Guano and the Opening of the Pacific World: a Global Ecological History” by G.T. Cushman (Cambridge University Press, 2013) [Book Review]

    Lowe, David J. (2017-12-31)

    Journal article
    University of Waikato

    This article reviews the book: "Guano and the Opening of the Pacific World: a Global Ecological History” by G.T. Cushman.

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  • Sensitive pyroclastic soils in the Bay of Plenty, New Zealand: microstructure to failure mechanisms

    Moon, Vicki G.; Mills, Pip R.; Kluger, Max O.; Lowe, David J.; Churchman, G.Jock; de Lange, Willem P.; Hepp, Daniel A.; Kreiter, Stefan; Mörz, T. (2017)

    Conference item
    University of Waikato

    Sensitive soils derived from weathered rhyolitic pyroclastic materials are associated with many landslides in the Bay of Plenty. Undrained, consolidated static triaxial tests show contractive p’-q’ plots, strain-softening stress-strain behaviour coupled with rising pore water pressures, shear band formation after peak strength, and considerable strain softening. Cyclic triaxial tests confirm brittle failure and extensive softening of the soil. Pore pressure gradients developed during shearing initiate collapse of clay microstructures into shear zones; further excess pore pressure generation in the shear zone leads to progressive failure. Halloysite, a low-activity clay mineral, is associated with sensitive layers within the pyroclastic sequences. Mushroom cap–shaped spheroidal halloysite results in weak short-range interactions between exposed clay surfaces on incomplete spheroids. This weak bonding allows disassociation of clay aggregates during slope failure, leading to strain softening and the development of flow post-failure.

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  • Is there a potassium-based solution to sensitive soil slipping within the Bay of Plenty?

    Robertson, Tom; Moon, Vicki G.; Lowe, David J. (2017)

    Conference item
    University of Waikato

    Landslides are common in sensitive, weathered pyroclastic soils in the Bay of Plenty (BOP). The clay mineralogy of these soils is dominated by halloysite, an inactive 1:1 clay mineral. Manipulation of cation content within the pore water of sensitive soils has been shown to improve in situ soil strength in illite-dominated soils in Norway. We present results of laboratory tests on the impact of altering cation status of a sensitive soil from the base of a large landslide at Omokoroa near Tauranga, BOP. Addition of KCl and KOH both reduced the liquid limit of the soil, a negative effect. In contrast, addition of K₂CO₃ caused an increase in the plasticity index of soil pastes. Soaking intact samples in K₂CO₃ for three weeks resulted in a considerable increase in peak stress in effective stress triaxial testing. These early results suggest that mitigation of sensitive soil landslides through increasing peak strength by addition of appropriate salts to the soil profile may be an option for mitigation of landslides in sensitive BOP soils.

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  • Evaluating soil and landscape models to predict liquefaction susceptibility in the Hinuera Formation, Hamilton Basin

    McKay, Aleesha; Lowe, David J.; Moon, Vicki G. (2017)

    Conference item
    University of Waikato

    Cone Penetration Tests (CPT) derived from the Hamilton section of the Waikato Expressway were analysed within CLiqTM software. The derived Liquefaction Potential Index (LPI) from each CPT was then combined with LIDAR, pedological and geological maps for statistical analysis. A soil model that incorporates the conditions of modern soil development with these derived LPI values was developed as a preliminary assessment tool for liquefaction potential within Hamilton Basin soils. The model shows that liquefaction is more likely to occur on interfluvial areas where there is little topographical relief. Pedological soils with high organic component are also a likely indicator of high liquefaction susceptibility.

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  • Correlating tephras and cryptotephras using glass compositional analyses and numerical and statistical methods: review and evaluation

    Lowe, David J.; Pearce, Nicholas J.G.; Jorgensen, Murray A.; Kuehn, Stephen C.; Tryon, Christian A.; Hayward, Chris L. (2017)

    Journal article
    University of Waikato

    We define tephras and cryptotephras and their components (mainly ash-sized particles of glass ± crystals in distal deposits) and summarize the basis of tephrochronology as a chronostratigraphic correlational and dating tool for palaeoenvironmental, geological, and archaeological research. We then document and appraise recent advances in analytical methods used to determine the major, minor, and trace elements of individual glass shards from tephra or cryptotephra deposits to aid their correlation and application. Protocols developed recently for the electron probe microanalysis of major elements in individual glass shards help to improve data quality and standardize reporting procedures. A narrow electron beam (diameter ~3-5 μm) can now be used to analyze smaller glass shards than previously attainable. Reliable analyses of ‘microshards’ (defined here as glass shards <10 μm) can be subject to significant element fractionation during analysis, but the systematic relationship of such fractionation with glass composition suggests that analyses for some elements at these resolutions may be quantifiable. In undertaking analyses, either by microprobe or LA-ICP-MS, reference material data acquired using the same procedure, and preferably from the same analytical session, should be presented alongside new analytical data. In part 2 of the review, we describe, critically assess, and recommend ways in which tephras or cryptotephras can be correlated (in conjunction with other information) using numerical or statistical analyses of compositional data. Statistical methods provide a less subjective means of dealing with analytical data pertaining to tephra components (usually glass or crystals/phenocrysts) than heuristic alternatives. They enable a better understanding of relationships among the data from multiple viewpoints to be developed and help quantify the degree of uncertainty in establishing correlations. In common with other scientific hypothesis testing, it is easier to infer using such analysis that two or more tephras are different rather than the same. Adding stratigraphic, chronological, spatial, or palaeoenvironmental data (i.e. multiple criteria) is usually necessary and allows for more robust correlations to be made. A two-stage approach is useful, the first focussed on differences in the mean composition of samples, or their range, which can be visualised graphically via scatterplot matrices or bivariate plots coupled with the use of statistical tools such as distance measures, similarity coefficients, hierarchical cluster analysis (informed by distance measures or similarity or cophenetic coefficients), and principal components analysis (PCA). Some statistical methods (cluster analysis, discriminant analysis) are referred to as ‘machine learning’ in the computing literature. The second stage examines sample variance and the degree of compositional similarity so that sample equivalence or otherwise can be established on a statistical basis. This stage may involve discriminant function analysis (DFA), support vector machines (SVMs), canonical variates analysis (CVA), and ANOVA or MANOVA (or its two-sample special case, the Hotelling two-sample T² test). Randomization tests can be used where distributional assumptions such as multivariate normality underlying parametric tests are doubtful. Compositional data may be transformed and scaled before being subjected to multivariate statistical procedures including calculation of distance matrices, hierarchical cluster analysis, and PCA. Such transformations may make the assumption of multivariate normality more appropriate. A sequential procedure using Mahalanobis distance and the Hotelling two-sample T² test is illustrated using glass major element data from trachytic to phonolitic Kenyan tephras. All these methods require a broad range of high-quality compositional data which can be used to compare ‘unknowns’ with reference (training) sets that are sufficiently complete to account for all possible correlatives, including tephras with heterogeneous glasses that contain multiple compositional groups. Currently, incomplete databases are tending to limit correlation efficacy. The development of an open, online global database to facilitate progress towards integrated, high-quality tephrostratigraphic frameworks for different regions is encouraged.

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  • Advancing tephrochronology as a global dating tool: applications in volcanology, archaeology, and palaeoclimatic research

    Lane, C.S.; Lowe, David J.; Blockley, S.P.E.; Suzuki, T.; Smith, V.C. (2017)

    Journal article
    University of Waikato

    Layers of far-travelled volcanic ash (tephra) from explosive volcanic eruptions provide stratigraphic and numerical dating horizons in sedimentary and volcanic sequences. Such tephra layers may be dispersed over tens to thousands of kilometres from source, reaching far beyond individual volcanic regions. Tephrochronology is consequently a truly global dating tool, with applications increasingly widespread across a range of Quaternary and geoscience disciplines. This special issue of the International Focus Group on Tephrochronology and Volcanism (INTAV) showcases some of the many recent advances in tephrochronology, from methodological developments to diverse applications across volcanological, archaeological, and palaeoclimatological research.

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  • Detection of thin tephra deposits in peat and organic lake sediments by rapid X-radiography and X-ray fluorescence techniques

    Lowe, David J.; Hogg, Alan G.; Hendy, C.H. (1981)

    Conference item
    University of Waikato

    This paper reports the application of the X-ray image process of X-radiography to unopened, small diameter organic sediment cores containing thin tephra deposits. Second, a rapid technique for detecting tephra layers in peat samples by X-ray fluorescence (XRF) analysis is described.

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  • Late Quaternary tephras in the Hamilton Basin, North Island, New Zealand

    Lowe, David J. (1981)

    Conference item
    University of Waikato

    This paper summarises the occurrence and distribution of late Quaternary tephras in the Hamilton (Middle Waikato) Basin and outlines a model to explain the pattern of soils formed from them. The collaborative work currently in progress on paleoecological aspects of the late Otiran - Aranuian history of the area is also reported.

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  • Tales of the unexpected: halloysite delivers surprises and a paradox

    Lowe, David J.; Churchman, G. Jock (2016)

    Unclassified
    University of Waikato

    Despite being first described nearly 200 years ago, halloysite still has the capacity to surprise. We report here the remarkable discovery in New Zealand of two new morphologies for this 1:1 Si:Al layered aluminosilicate member of the kaolin subgroup. One discovery was entirely serendipitous, thus lending validity to the famous phrase attributed to scientist Isaac Asimov: The most exciting phrase to hear in science, the one that heralds new discoveries, is not “Eureka” but “That’s funny...”. Moreover, the recognition of one of the new morphologies of halloysite helped enable a long-standing problem regarding the geotechnical property of sensitivity and its impact on landsliding in the Tauranga region, eastern North Island, to be solved. Such landsliding has commonly been attributed (possibly erroneously) to the dominance of nanocrystalline allophane, the clay commonly associated with halloysite in many weathered pyroclastic sequences and volcanogenic soils in North Island. In this article, we briefly summarise the circumstances and implications of the two discoveries relating to halloysite morphology, one published in Clay Minerals and the other in Geology, and a third study (also in Clay Minerals) relating in part to the formation of halloysite.

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  • A new attraction-detachment model for explaining flow sliding in clay-rich tephras

    Kluger, Max O.; Moon, Vicki G.; Kreiter, Stefan; Lowe, David J.; Churchman, G.Jock; Hepp, Daniel A.; Seibel, David; Jorat, M. Ehsan; Mörz, Tobias (2017-02-01)

    Journal article
    University of Waikato

    Altered pyroclastic (tephra) deposits are highly susceptible to landsliding, leading to fatali-ties and property damage every year. Halloysite, a low-activity clay mineral, is commonly associated with landslide-prone layers within altered tephra successions, especially in depos-its with high sensitivity, which describes the post-failure strength loss. However, the precise role of halloysite in the development of sensitivity, and thus in sudden and unpredictable landsliding, is unknown. Here we show that an abundance of mushroom cap–shaped (MCS) spheroidal halloysite governs the development of sensitivity, and hence proneness to landslid-ing, in altered rhyolitic tephras, North Island, New Zealand. We found that a highly sensitive layer, which was involved in a flow slide, has a remarkably high content of aggregated MCS spheroids with substantial openings on one side. We suggest that short-range electrostatic and van der Waals interactions enabled the MCS spheroids to form interconnected aggre-gates by attraction between the edges of numerous paired silanol and aluminol sheets that are exposed in the openings and the convex silanol faces on the exterior surfaces of adjacent MCS spheroids. If these weak attractions are overcome during slope failure, multiple, weakly attracted MCS spheroids can be separated from one another, and the prevailing repulsion between exterior MCS surfaces results in a low remolded shear strength, a high sensitivity, and a high propensity for flow sliding. The evidence indicates that the attraction-detachment model explains the high sensitivity and contributes to an improved understanding of the mechanisms of flow sliding in sensitive, altered tephras rich in spheroidal halloysite.

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  • The lore of lakes

    Green, John D.; Lowe, David J. (1992)

    Journal article
    University of Waikato

    Studies of lakes and their many layers of silt and sediment can tell us a great deal, from centuries-old deforestation practices to the climate changes over thousands of years. The study of the history of lake ecosystems is a fast developing field known as palaeolimnology.

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  • Introduction to tephra-derived soils, North Island, New Zealand: University of Waikato and University of Wisconsin-Platteville post-conference Andisol excursion, 21-23 December, 2016

    Lowe, David J. (2016-12-21)

    Report
    University of Waikato

    Provisional itinerary DAY 1 Wednesday 21 December: Mamaku Plateau-Rerewhakaaitu-Lake Tarawera: 1 Goodwin Farm, Tapapa Rd, Tapapa: welded ignimbrite, tephras, loess, buried soils (Tirau soil) - stratigraphy of sequence (230 ka and younger) and upbuilding pedogenesis - Tirau silt loam 2 Brett Rd, Rerewhakaaitu: Holocene tephras and buried soil (Rotomahana soil) - Volcanic landscape, historical importance of area for NZ soil survey - Stratigraphy of sequence (~9.5 cal ka to 10 June 1886 Tarawera eruption) and upbuilding pedogenesis - Rotomahana sandy loam, 3 Ash Pit Rd, Rerewhakaaitu: tephras and buried soils (Matahina soil) - Matahina gravel - buried spodic/podzol soil features, 4 Okareka Loop Rd tephra section with proximal Rotorua Tephra and buried soils, loess, Buried Village Museum, Te Wairoa, Lake Tarawera (Stoney Point). DAY 2 Thursday 22 December: Otorohanga-Waitomo Caves -Pirongia Mountain: 1 Raynes Road section: Ultisol in composite tephra sequence (Kainui soil), 2 Otorohanga Kiwi House, 3 Waitomo Caves,, 4 Pirongia Mountain: Mangakara forest walk, 5 Evening meal on an Andisol. DAY 3 Friday 23 December: Hobbiton, Hamilton gardens including Te Parapara (ancient Maori garden): 1. Hobbiton tour 10.15 am (2 hrs), 2. Hamilton Gardens incl. Te Parapara Garden and human-modified soils (Tamahere soil).

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  • Guidebook for Rangitoto Island AQUA field trip, Auckland, 2016

    Lowe, David J.; Shane, Phil A.R.; de Lange, Peter J.; Clarkson, Bruce D. (2016)

    Conference item
    University of Waikato

    Rangitoto is arguably Auckland’s most beautiful and omnipresent landscape feature. It is a symmetrical, ~6-km wide, basaltic shield volcano that last erupted ~550‒500 cal. yr BP (c. 1400‒1450 AD), not long after the arrival and settlement of Polynesians in the Auckland region (c. 1280 AD). It is by far the largest, and the youngest, volcano in the Auckland Volcanic Field (AVF). The AVF consists of approximately 53 individual eruptive centres, all of which are within the boundaries of the Auckland urban area. Recent research on cryptotephras (defined below) in sediments from Lake Pupuke on North Shore and in wetlands on Motutapu Island, and on a 150-m-long drill core obtained in February, 2014, has revealed that Rangitoto has a much more complex history that previously thought, and may be better viewed as a ‘volcanic complex with multiple episodes of eruptions’ (Linnell et al. 2016). In summary, (1) activity commenced c. 6000 cal. yr BP involving minor effusive and pyroclastic volcanism; (2) a voluminous shield-building phase took place from c. 650550 cal. yr BP (c. 13001400 AD), forming the main island ediface; and (3) the final phase of activity, from c. 550500 cal. yr BP (c. 14001450 AD), was explosive and less voluminous, producing scoria cones at the summit. The flora on Rangitoto is unique among the islands situated in the Hauraki Gulf because of the island’s young age, and the fact that technically Rangitoto is an ‘oceanic’ island. Its flora and fauna are derived entirely from long distance dispersal. The island contains some 582 vascular plant taxa of which 228 (39%) are indigenous. Various other special ecological features, and studies on plant succession and their drivers, make the island a truly fascinating place to visit. At this time of year, we should see many pohutukawa (Metrosideros excelsa) trees in flower.

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  • The time machine. Norman Taylor Memorial Lecture 2002

    Lowe, David J. (2002)

    Conference item
    University of Waikato

    I've chosen to talk about five topics dealing with longstanding pedological or paleoenvironmental problems involving tephrostratigraphy. I'll begin with the oldest tephras and work 'stratigraphically upwards' to the youngest. Along the way I'll mention or show a few of the people I've worked with, or who were involved historically in the research areas. I've allowed around five or six minutes for each topic (but I'd be grateful if you didn't set your stopwatches!). As promised, the second part of the talk will begin when we reach the year 1952. Among a range of personal observations relating to the birth of the society and to Norman Taylor, I will attempt to explain how I came to be giving this lecture today.

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  • Rangitoto volcano excursion, Auckland. Pre-conference field trip

    Lowe, David J.; Kenedi, Kate Lewis; de Lange, Peter J. (2014-08-30)

    Conference item
    University of Waikato

    Rangitoto is one of Auckland City’s more iconic landscape features. Guarding the entrance to the Waitemata Harbour, Rangitoto is a symmetrical, ~6-km wide, basaltic shield volcano that last erupted ~550 years ago shortly after the arrival and settlement of Polynesians in the Auckland region (c. 1280 AD). Rangitoto is by far the largest, and also the youngest, volcano in the Auckland Volcanic Field (AVF). The AVF is a monogenetic volcanic field consisting of approximately 53 individual eruptive centres, all of which are within the boundaries of the Auckland urban area. Recent research has revealed more about Rangitoto’s eruptive history, which may date back to c. 1500 years ago (Shane et al. 2013). Some of these findings have been noted below and will be discussed further while we ascend its summit and explore its various landscape and vegetational features.

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  • Discovery of halloysite books in altered silicic Quaternary tephras, northern New Zealand

    Cunningham, Michael J.; Lowe, David J.; Wyatt, Justin Burns; Moon, Vicki G.; Churchman, G. Jock (2016-10-11)

    Journal article
    University of Waikato

    Hydrated halloysite was discovered in books, a morphology previously associated exclusively with kaolinite. From ~1.5 μm to ~1500 μm in length, the books showed significantly greater mean Fe contents (Fe2O3 = 5.2 wt%) than tubes (Fe2O3 = 3.2 wt%), and expanded rapidly with formamide. They occurred, along with halloysite tubes, spheroids, and plates, in highly porous yet poorly-permeable, silt-dominated, Si-rich, pumiceous rhyolitic tephra deposits aged ~0.93 Ma (Te Puna tephra) and ~0.27 Ma (Te Ranga tephra) at three sites ~10-20 m stratigraphically below the modern land-surface in the Tauranga area, eastern North Island, New Zealand. The book-bearing tephras were at or near saturation, but have experienced intermittent partial drying, favouring the proposed changes: solubilized volcanic glass + plagioclase -> halloysite spheroids -> halloysite tubes -> halloysite plates -> halloysite books. Unlike parallel studies elsewhere involving both halloysite and kaolinite, kaolinite has not formed in Tauranga presumably because the low permeability ensures the sites largely remain locally wet so that the halloysite books are metastable. An implication of the discovery is that some halloysite books in similar settings may have been misidentified previously as kaolinite.

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  • Unique but diverse: some observations on the formation, structure, and morphology of halloysite

    Churchman, G. Jock; Pasbakhsh, Pooria; Lowe, David J.; Theng, B.K.G. (2016-10-11)

    Journal article
    University of Waikato

    New insights from the recent literature are summarised and new data presented concerning the formation, structure and morphology of halloysite. Halloysite formation by weathering always requires the presence of water. Where substantial drying occurs, kaolinite is formed instead. Halloysite formation is favoured by a low pH. The octahedral sheet is positively charged at pH < ~8, whereas the tetrahedral sheet is negatively charged at pH > ~2. The opposing sheet charge would facilitate interlayer uptake of H₂O molecules. When halloysite intercalates certain polar organic molecules, additional (hkl) reflections appear in the X-ray diffractogram, suggesting layer re-arrangement which, however, is dissimilar to that in kaolinite. Associated oxides and oxyhydroxides of Fe and Mn may limit the growth of halloysite particles as does incorporation of Fe into the structure. Particles of different shape and iron content may occur within a given sample of halloysite.

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  • The working life of John McCraw (1925-2014): a remarkable New Zealand pedologist and Earth scientist

    Nelson, Campbell S.; Lowe, David J.; Tonkin, Philip J. (2015)

    Journal article
    University of Waikato

    John McCraw was an Earth scientist who began working as a pedologist with Soil Bureau, DSIR, then became the Foundation Professor of Earth Sciences at the University of Waikato in Hamilton, inspiring a new generation to study and work in Earth sciences, a discipline he introduced into the tertiary education system in New Zealand. In retirement, he was an author and historian with a special emphasis on Central Otago as well as the Waikato region. Throughout his career, marked especially by meritorious leadership, accomplished administration, and commitment to his staff and students at the University of Waikato, John McCraw also contributed widely to the communities in which he lived through public service organizations and as a public speaker. He received a number of awards including an MBE, fellowship, and companionship, and, uniquely, is commemorated also with a glacier, a fossil, and a museum-based research room named for him. The Earth sciences programme today as an integral part of the School of Science at the University of Waikato is stronger than ever. In the past few years several new staff have been appointed, both academic and technical, giving the largest-ever Earth sciences team of about 30 staff. As well as research-led teaching, Earth sciences has strong research groups, at the cores of which are doctoral and masterate students, and postdoctoral fellows, to carry on the work envisaged by John McCraw all those years ago. This thriving continuation of our discipline, which has always had strong multidisciplinary linkages with other sciences, is − alongside the countless students he has taught and inspired − surely his greatest legacy.

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  • The effect of climate on lake mixing patterns and temperatures

    Green, John D.; Viner, A.B.; Lowe, David J. (1987)

    Book item
    University of Waikato

    The maritime geographical location has been said to give distinctive characteristics of water mixing to lakes (Hutchinson 1957, pp. 443-444), but such effects have never been described in detail. New Zealand's lakes should exemplify well these maritime distinctions, and in this chapter features of water column mixing and temperature changes are identified which can distinguish New Zealand lakes from those elsewhere.

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