Browsing by Author "Wong, HKY"

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    A 7300 year record of environmental changes in a coastal wetland (Moawhitu), New Zealand, and evidence for catastrophic overwash (tsunami?)
    (Elsevier, 2020-09) Chagué, C; Cope, J; Kilroy, C; Jacobsen, GE; Zawadzki, A; Wong, HKY
    Three sedimentary sequences from a coastal wetland behind a sand barrier, on the west coast of d'Urville Island, New Zealand, were examined using a multi-proxy approach, including sedimentological, geochemical and microfossil (diatom) analyses, with the chronology established using radiocarbon and 210Pb dating. Data show that a brackish lagoon started developing 7300 year ago after formation of the sand barrier in Moawhitu. This was followed by periods of alternating wetland encroachment and open water, displaying spatial variations, until a peatland was established about 1300 cal. yr BP. The wetland was then partially drained in the early 1900s, leading to compaction of the peat near the surface. A coarse layer containing gravel, sand and shells, with a sharp lower contact, in the northern area of the wetland, is attributed to an overwash about 2500–3000 yr BP, most probably a tsunami generated by the rupture of a local or regional fault. The high-resolution continuous record obtained with XRF core scanning revealed a geochemical signature (Ca and S) for the overwash 600 m inland in the middle area of the wetland, while it was absent from the southern site 1.1 km from the shore. This suggests that, except at the northern end of Moawhitu, the sand dune acted as an effective barrier preventing any sediment from overtopping 2500–3000 yr BP, with only a geochemical evidence marking the extent of seawater inundation. No sedimentological or geochemical evidence could be found in the wetland for the 15th century tsunami that had destroyed almost an entire community in Moawhitu, as recounted in Māori oral tradition (pūrākau), although pebbles at the surface of the dune are likely to be linked to this event. Thus, the sand dune appears to have again acted as an effective barrier for the overwash in the 15th century. However, our study suggests that the area might have been impacted by more than one tsunami in the last 3000 years. It also shows that a high-resolution continuous XRF record can provide the evidence for short-term changes (catastrophic or not) that did not leave any clear sedimentological signature, thus providing a better insight of environmental changes in any depositional environment. © 2020 Elsevier B.V
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    Assessing the impacts of scale residues from offshore oil and gas decommissioning on marine organisms
    (CSIRO Publishing, 2021-07-02) Cresswell, T; Brown, S; Wong, HKY; Apte, S
    Successful decommissioning of offshore oil and gas infrastructure requires an effective and safe approach to assessing and managing chemical and radiological residues. Scale frequently accumulates on the interior surfaces of pipes and other structures and may persist long after extraction operations have ceased. Scale materials can contain a range of metal contaminants (including mercury), as well as naturally occurring radioactive materials. In newer or more accessible infrastructure, the scale is routinely removed, and becomes a waste product. The persistent nature of scale contaminants can result in a radiological dose to the organisms living on, or near an intact pipeline. Eventually, infrastructure corrosion following in situ decommissioning (abandonment) could lead to metal and radionuclide contaminants being accessible to the surrounding seafloor environment, where bioaccumulation and subsequent ecotoxicological effects from the chemical and radiological properties of the scale could occur. The paper describes a tiered approach to assess the ecological impacts of pipeline scale in order to assist operators with their plans for decommissioning offshore infrastructure, especially when considering ‘leave in place’ options. © CSIRO 2021
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    Assessing the risk of NORM scale to marine biota from offshore oil and gas decommissioning
    (International Atomic Energy Agency, 2020-10-19) Creswell, T; Apte, S; Wong, HKY; Brown, S
    Successful decommissioning of offshore oil and gas infrastructure requires an effective and safe approach to assessing and managing chemical and radiological residues. Scale residues frequently accumulate on the interior surfaces of pipes and other structures, and may persist long after extraction operations have ceased. Scale materials can consist of a range of metal contaminants (including mercury), as well as naturally occurring radioactive materials (NORM). In newer infrastructure, the scale is cleaned routinely, and becomes a waste product. The persistent nature of ‘NORM scale’ can result in a radiological dose to the organisms living on, or near an intact pipeline. Eventually, pipe corrosion could lead to metal and radionuclide contaminants being accessible to the surrounding benthic environment, where bioaccumulation and subsequent ecotoxicological effects from the chemical and radiological properties of the scale could occur. This presentation describes a multi-phase approach to assessing the ecological impacts of pipeline scale in order to assist operators with their plans for decommissioning offshore infrastructure. Recent results from pipeline scale testing will be discussed.
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    Challenges in the radiochemical separation of marine samples from the Montebello Islands
    (South Pacific Environmental Radioactivity Association, 2018-11-06) Thiruvoth, S; Child, DP; Harrison, JJ; Johansen, MP; Silitonga, A; Vardanega, CR; Wilsher, KL; Wong, HKY
    The Montebello Islands, located off the North Western coast of Western Australia, was used as a nuclear weapons test site by the British government in the 1950s. Three nuclear tests were conducted around the islands. The first in 1952 (W818) detonated in the hull of the HMS Plym anchored in 12 m of water between Alpha and Trimouille Islands, and the second and third tests (MOSAIC G1 and G2) were detonated on 30 m Aluminium towers in May and June 1956, G1 on the Northern Western tip of Trimouille island and G2, the largest test conducted in Australian territory, on Alpha island. The fallout from these tests deposited long-lived anthropogenic radionuclides on nearby islands and ocean surface, host to an array of animals and plants. Marine sand, marine sediment, algae, fish, turtles and turtle eggs, among others, were sampled from the surrounding zones for dose assessment studies, thirty-nine of which were processed for actinide and strontium analysis. Due to the expected presence of discrete radioactive particles in some matrices a three step digestion method was applied to obtain complete dissolution of sample material. To overcome sample heterogeneity, the digest solution was sub-sampled for actinide and Sr-90 analysis by alpha spectrometry and liquid scintillation analysis, for plutonium isotopic analysis by AMS, and for elemental analysis by ICPAES/MS. The radiochemical separation method developed at ANSTO for Am, Pu, Th, U, and Sr for terrestrial soils and sediments (Harrison et al, 2011) was adapted to samples from the marine environment. However, some sample matrices proved to be challenging in achieving acceptable chemical recoveries of strontium due to the high concentrations of native calcium. This current study will discuss the methods used, and challenges overcome, in radiochemical separation for alpha spectrometry and liquid scintillation analysis for a wide range of sample types.
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    Characterising the expression of sub-millennial scale climate events in western Europe during the early last glacial period using multi-proxy speleothem records
    (Australasian Quaternary Association Inc., 2022-12-06) Corrick, E; Drysdale, RN; Hellstrom, JC; Couchoud, I; Wong, HKY; Didier, C; Hai, C; Jaillet, S; Tocino, S
    Past abrupt climate changes act as critical analogues for understanding how the climate system may respond to future abrupt changes. One of the best examples of naturally occurring abrupt climate change is the series of millennial-scale Dansgaard-Oeschger (D-O) events that took place during the last glacial period (115,000 – 11,500 years ago). D-O events are clearly recorded in ice-cores from Greenland, with coincident climate changes detected in marine and terrestrial records spanning a range of climate zones. Greenland ice cores also record shorter-lived ‘sub-millennial’ scale events that occur within the main D-O event sequence, particularly during the early last glacial period. To what extent these sub-millennial events were expressed outside of Greenland is currently poorly understood. Here we characterise the response to sub-millennial scale climate changes in western Europe using five multi-proxy (δ18O, δ13C, Mg and Sr) speleothem records from Saint-Marcel and Orgnac Caves, France, that collectively span 127 – 87 kyr BP. The replicated speleothem records clearly preserve both millennial D-O events and sub-millennial events, demonstrating the strong coupling between the climate of south-east France and the North Atlantic across both millennial and sub-millennial timescales. Interestingly, the multiproxy record reveals a decoupling between broad temperature (indicated by δ13C) and precipitation changes (indicated by δ18O) during some of these sub-millennial scale events. This suggests that climate teleconnections operating during sub-millennial events were in some ways different to those during the stronger millennial-scale D-O events.
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    Combustion completeness and sample location determine wildfire ash leachate chemistry
    (American Geophysical Union, 2024-05-21) Campbell, M; Treble, PC; McDonough, LK; Naeher, S; Baker, AA; Grierson, PF; Wong, HKY; Andersen, MS
    Understanding past fire regimes and how they vary with climate, human activity, and vegetation patterns is fundamental to the mitigation and management of changing fire regimes as anthropogenic climate change progresses. Ash‐derived trace elements and pyrogenic biomarkers from speleothems have recently been shown to record past fire activity in speleothems from both Australia and North America. This calls for an empirical study of ash geochemistry to aid the interpretation of speleothem palaeofire proxy records. Here we present analyses of leached ashes collected following fires in southwest and southeast Australia. We include a suite of inorganic elemental data from the water‐soluble fraction of ash as well as a selection of organic analytes (pyrogenic lipid biomarkers). We also present elemental data from leachates of soils collected from sites in southwest Australia. We demonstrate that the water‐soluble fraction of ash differs from the water‐soluble fraction of soils, with trace and minor element concentrations in ash leachates varying with combustion completeness (burn severity) and sample location. Changes in some lipid biomarker concentrations extracted from ashes may reflect burn severity. Our results contribute to building a process‐based understanding of how speleothem geochemistry may record fire frequency and severity, and suggest that more research is needed to understand the transport pathways for the inclusion of pyrogenic biomarkers in speleothems. Our results also demonstrate that potential contaminant loads from ashes are much higher than from soils, with implications for the management of karst catchments, which are a critical water resource. © 2024 The Author(s). Geochemistry,Geophysics, Geosystems published by Wiley Periodicals LLC on behalf of American Geophysical Union. This is an open access article under the terms of the Creative Commons Attribution License, which permits use,distribution and reproduction in any medium, provided the original work is properly cited
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    A DNA-based assay for toxic chemicals in wastewater
    (Wiley-Blackwell, 2011-08-01) Foreman, AL; Philips, L; Kanellis, VG; Hammoudeh, D; Naumann, C; Wong, HKY; Chisari, R; Hibbert, DB; Lee, GSH; Patra, R; Julli, M; Chapman, J; Cooke, AR; dos Remedios, CG
    Chemical toxicants, particularly metal ions, are a major contaminant in global waterways. Live-organism bioassays used to monitor chemical toxicants commonly involve measurements of activity or survival of a freshwater cladoceran (Ceriodaphnia dubia) or light emitted by the marine bacterium Vibrio fischeri, used in the commercial Microtox (R) bioassay. Here we describe a novel molecule-based assay system employing DNA as the chemical biosensor. Metals bind to DNA, causing structural changes that expel a bound (intercalated) fluorescent reporter dye. Analyses of test data using 48 wastewater samples potentially contaminated by metal ions show that the DNA-dye assay results correlate with those from C. dubia and Microtox bioassays. All three assays exhibit additive, antagonistic, and synergistic responses that cannot be predicted by knowing individual metal concentrations. Analyses of metals in these samples imply the presence of chemical toxicants other than metal ions. The DNA-dye assay is robust, has a 12-month shelf life, and is only slightly affected by sample pH in the range 4 to 9. The assay is completed in a matter of minutes, and its portability makes it well suited as a screening assay for use in the field. We conclude that the DNA-dye test is a surrogate bioassay suitable for screening chemical toxicity. Environ. Toxicol. Chem. 2011;30:1810-1818. (C) 2011 SETAC
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    Environmental impact assessment of the 2011 Tohoku-oki tsunami on the Sendai Plain
    (Elsevier B.V., 2012-12-30) Chagué-Goff, C; Niedzielski, P; Wong, HKY; Szczuciński, W; Sugawara, D; Goff, JR
    Large areas of farmland in the Sendai Plain, Japan, were inundated by the 11 March 2011 Tohoku-oki tsunami and covered by a discontinuous 30–0.2 cm thick sediment layer consisting of sand and/or mud and generally thinning and fining inland. Two months after the tsunami, numerous rice paddy fields and depressions remained ponded with brackish or saline water. A series of field surveys in May, August and October 2011 were carried out north of Sendai airport, in order to assess the environmental impact of the tsunami. While evaporation had resulted in elevated conductivity in ponded water in May (up to 68.2 mS cm− 1), rainfall over the next five months led to dilution, although brackish water was still recorded in depressions and on paddy fields. Tsunami sediments, underlying soil and soil beyond the tsunami inundation limit were collected at 43 sites along and near a transect extending over 5 km inland, and analysed for grain size, organic content, water leachable ions, acid leachable metals and exchangeable metalloids. Water leachable anion and cation concentrations were elevated in sandy and muddy tsunami deposits and soils particularly in areas, where seawater had stagnated for a longer period of time after the tsunami, with up to 10.5% Cl, 6.6% Na, 2.8% SO4, 440 mg kg− 1 Br measured in surface sediments (< 0.5 cm depth). Vertical variations were also recorded, with higher concentrations often measured in the surface samples. A similar trend could be observed for some of the metalloids (As) and metals (Zn, Cu and Ni), although in general, maximum concentrations of metals and metalloids were not much higher than in soils not inundated by the tsunami and were within background levels for uncontaminated Japanese soils. The impact of saltwater inundation was documented in the chemistry of soils underlying tsunami sediments, which were affected by salt contamination down to ~ 15 cm depth, and soils not covered by tsunami deposits. The latter implies that the extent of tsunami inundation may successfully be determined using geochemical markers in absence of any sedimentological evidence. Water leachable ions mostly decreased over time, however, they remained high enough to impact on rice farming, which was completely halted in 2011. Although further work is required to assess the longer term impact of tsunami inundation, flushing of salt with freshwater, as well as the possible removal of sandy/muddy sediments and underlying soil are recommended to allow crop production to resume. © 2020 Elsevier B.V.
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    Equatorial Pacific coral geochemical records show recent weakening of the Walker Circulation
    (American Geophysical Union, 2014-11-10) Carilli, JE; McGregor, HV; Gaudry, JJ; Donner, SD; Gagan, MK; Stevenson, S; Wong, HKY; Fink, D
    Equatorial Pacific ocean-atmosphere interactions affect climate globally, and a key component of the coupled system is the Walker Circulation, which is driven by sea surface temperature (SST) gradients across the equatorial Pacific. There is conflicting evidence as to whether the SST gradient and Walker Circulation have strengthened or weakened over the late twentieth century. We present new records of SST and sea surface salinity (SSS) spanning 1959–2010 based on paired measurements of Sr/Ca and δ18O in a massive Porites coral from Butaritari atoll in the Gilbert Islands, Republic of Kiribati, in the central western equatorial Pacific. The records show 2–7 year variability correlated with the El Niño–Southern Oscillation (ENSO) and corresponding shifts in the extent of the Indo-Pacific Warm Pool, and decadal-scale signals related to the Pacific Decadal Oscillation and the Pacific Warm Pool Index. In addition, the Butaritari coral records reveal a small but significant increase in SST (0.39°C) from 1959 to 2010 with no accompanying change in SSS, a trend that persists even when ENSO variability is removed. In contrast, larger increases in SST and SSS are evident in coral records from the equatorial Pacific Line Islands, located east of Butaritari. Taken together, the equatorial Pacific coral records suggest an overall reduction in the east-west SST and SSS gradient over the last several decades, and a recent weakening of the Walker Circulation. © 2014, American Geophysical Union. All Rights Reserved.
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    Establishing a radioanalytical capability to support reactor decommissioning
    (South Pacific Environmental Radioactivity Association, 2018-11-06) Harrison, JJ; Martiniello, J; Mokhber-Shahin, L; Rowling, B; Silitonga, AS; Thiruvoth, S; Vardenega, C; Van De Voorde, R; Wilsher, KL; Wong, HKY
    Australia’s first reactor, the 1O megawatt High Flux Australian Reactor (HIFAR) vi/as operated between 1958 and 2007. HIFAR was one of six DIDO reactors which were installed in the UK, Denmark, Germany and Australia. HIFAR was a multi-purpose reactor, initially used for nuclear material research followed by production of medical radioisotope; an: neutron diffraction experiments. Atter HIFAR was closed, a process of decommissioning commenced. Initially, internal components such as the fuel and heavy water (which acted as primary coolant and neutron moderator) were removed. Currently, HIFAR is in a “care and maintenance" phase whereby short-lived radionuclides can decay and non-radioactive equipment and instrumentation removed. Approximately 1OO research and power reactors have been decommissioned around the world including two of the DIDO class reactors at Harwell, UK and Risø, Denmark. ANSTO can draw on international experience as we as well as experience gained during decommissioning of its own 100 kilowatt Moata reactor in 2010. Accurate identification and quantification of radioactivity is a critical safety, environmental and economic aspect of any nuclear reactor decommissioning project as it supports decision making around long-term storage of disposal options of reactor materials as well as environmental assessment of the reactor site. A capability to quantify typical radionuclides found in reactor materials and environmental samples is being developed at ANSTO. Reactor materials that may require assessment include concrete, graphite and steel and environmental samples include soils and waters. Radionuclides of interest are predominantly beta- and gamma-emitting fission and activation products. Non—destructive, high resolution gamma spectrometry will be applied to quantify gamma emitting radionuclides such as 60Co, 66Zn, 133 Ba, 137Cs, 152 Eu, and 154Eu. The complex matrix of some reactor materials will cause attenuation of gamma photons and empirical and/or theoretical corrections will be applied. Beta-emitting radionuclides with weak or no gamma emission lines cannot be easily identified or quantified in solid materials using non-destructive techniques. This is due to attenuation of the beta particles, the nature of the beta emission spectrum and interferences from other beta- and gamma-emitting radionuclides. A suite of destructive radioanalytical techniques, designed to isolate and quantify beta-emitting radionuclides such as 3H, 14C, 36CI, 55Fe, 63Ni, 98Sr and 99Tc is being developed. This paper will present the timeline for development and the progress to date of this radioanalytical capability which will support the current and future decommissioning needs of Australia and our region.
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    Estimating diffusion in heterogeneous groundwater systems using short-llived radio-isotopes and stable isotopes or bromine
    (Geological Society of Australia, 2014-07-07) Peterson, MA; Cendón, DI; Andersen, MS; Mokhber-Shahin, L; Wong, HKY; Rowling, B
    Diffusion is an important and ubiquitous phenomenon in nature, but too often neglected or unmeasured in water resource hydrogeology or solute transport. Diffusion may, in fact, be the dominant process that dictates hydrogeochemistry and affects tracers. Conservative and age tracers are commonly used for water resource or contaminant plume transport estimations, but will give misleading results, if diffusion is ignored. Diffusion of tracers into aquitards, matrix pores of fractured rocks, blind fractures or other low conductivity zones lead to retardation and possible adsorption, exchange, precipitation or decay. This becomes increasingly important as heterogeneity of flow domains increase, for example, in fractured rock aquifers, interlayered sediments or aquifers associated with aquitards. Traditional methods of measuring diffusion coefficients in small slices of heterogeneous rock are unreliable for upscaling, so this study presents an alternative method based on lab-scale drill-core tests and suggests field-scale borehole tracer tests. Fick’s first law shows that diffusion rates are driven by concentration gradients. Short-lived radiotracers soon reach a steady-state concentration gradient with enhanced flux where diffusion rate equals decay, while stable tracers trend towards saturation and ever-decreasing fluxes. We compare diffusion of short-lived radiotracers 131I half-life 8 days) or 82Br (half-life 1.5 days) to their stable equivalent (I or Br) into 45–50 cm lengths of ~60 mm diameter drill core. Five cores were selected from three fractured rock environments: sandstone, limestone and metavolcanics. By regularly sampling and refilling the annulus with tracers around the enclosed core, we are able to discern differential in-diffusion between stable- and radio-tracers. For example, the annulus was sampled and refilled weekly with an (equivalent decayed) 131I activity of 22 Bq/g and within three weeks (2.6 half-lives) each core had reached a characteristic steady state flux. The net fluxes were 7 around 1.0 Bq/cm2/week in the sandstone cores, 0.2 Bq/cm2/week in the metavolcanics, and 0.05 Bq/cm2/week in the limestone. This was compared to stable iodine weekly refills at 2.6 mg/L, which gave ever-diminishing diffusion results. The net fluxes of stable iodine diminished steadily, e.g. over three weeks from 98 to 26 ng/cm2/week for the most porous (medium sandstone ~15%), and from 11 to 7 ng/cm2/week for the least porous (limestone ~2%). Experiments were also performed using 82Br and stable bromine, with sampling and refills performed on a daily (0.68 half-lives) basis. Similar trends were apparent, though the data was noisier due to more frequent refills and less time for diffusion to generate significant changes in the annulus reservoir solutions. This method enables analysis of drill cores for comparative effective diffusion coefficients of different systems. Quantitative interpretation is currently being refined. In principle, the method should be transferrable to single boreholes or tracer tests between multiple boreholes to gain larger scale representation of effective diffusion within a groundwater system. The normally confounding factors, such as dilution, advection, exchange, adsorption and precipitation, are negated by comparing the stable with radio-tracer results, as all isotopes of these elements are identically affected by such processes and losses. © Geological Society of Australia Inc
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    Evidence of wet-dry cycles and mega-droughts in the Eemian climate of southeast Australia
    (Springer Nature, 2020-10-22) McGowan, HA; Campbell, M; Callow, JN; Lowry, A; Wong, HKY
    Understanding past climate variability is critical to informing debate of likely impacts of global warming on weather and climate, and water resources. Here we present a near annual resolution reconstruction of climate developed from a speleothem that spans the Eemian [Marine Isotope Stage 5e (MIS 5e)] from 117,500 to 123,500 years BP—the most recent period in the Earth’s history when temperatures were similar to those of today. Using 25 Mg, 88Sr, and 137Ba as proxies, we show the first indication of solar and teleconnection cyclic forcing of Eemian climate in southeast Australia, a region at present often affected by severe drought and bushfires. We find evidence for multi-centennial dry periods interpreted as mega-droughts, and highlight the importance of understanding the causes of these in the context of a rapidly warming world, where temperatures are now, or projected to exceed those of the Eemian. © The Author(s) 2020
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    Final report on a field study of soil-to-plant transfer of radioactive caesium, strontium and zinc in tropical Northern Australia to the IAEA/FAO/IUR CRP on classification of soils systems on the basis of transfer factors of radionuclides from soil to reference plants
    (Australian Nuclear Science and Technology Organisation, 2003-09) Twining, JR; Shotton, P; Tagami, K; Payne, TE; Itakura, T; Russell, RA; Wilde, KL; McOrist, GD; Wong, HKY
    Soil-to-plant radionuclide transfer factors for cesium (134Cs), strontium (85Sr) and zinc (65Zn) into sorghum and mung plants grown in tropical Australia have been determined over a four-year study period. The crops were grown on two types of red earth soils. Transfer factors for Cs and Sr are not substantially different from the expected values based on previous studies, reported in the general literature and compiled in the IUR database, mainly performed within temperate climates. In contrast, the values for zinc (Zn) are more than an order of magnitude greater than anticipated. Most of the radioactivity added to the soils has been retained in the top 5 cm of both soils. There has been a general decline in soil-to-plant transfer of Cs and Zn as time has increased.
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    Geochemical indicators and diatoms as true markers of the inundation limit of the 2010 Maule Tsunami
    (American Geophysical Union, 2013-01-12) Chagué-Goff, C; Goff, JR; Wong, HKY; Cisternas, M
    It has long been known that tsunamis inundate further than the limit of the sand deposit they leave behind, and that relying on the extent of the sandy sedimentary evidence is likely to result in an under-estimation of event magnitude and risk. However, the question remains about how to identify the real limit of tsunami inundation, particularly several months or more after the event. Here we report on a study carried out at a site on the Pacific coast of Chile south of Constitución in August 2010, nearly 6 months after the Mw 8.8 Maule tsunami. Eight pits were dug along a 480 m long shore-perpendicular transect, incorporating the area covered by tsunami sediment, a zone covered by a discontinuous and decomposing debris scatter up to the point of maximum inundation, and an area further landward from this point. The tsunami sand deposit extended from ~160 to 260 m inland and ranged in thickness from 22 to less than 1 cm at the limit of sediment deposition. It consisted of dark, generally well-sorted, coarse to medium sand. Logs, pumice and various organic debris were found up to a limit of tsunami inundation (380 m inland - confirmed by a local eye witness). New grass growth also covered the tsunami deposit and the field further inland. While the chemical composition of the tsunami deposit differed to that of the underlying soil, indicators of saltwater inundation were low in the sandy units, reflecting downward leaching and dilution by rainfall in the porous material in the 6 months since the tsunami. Concentrations of saltwater indicators (e.g. chloride, sulphate, bromide) were however elevated in the area covered by scattered debris up to the limit of tsunami inundation, suggesting preferential retention in organic-rich material. Marine and brackish-marine diatoms were found both in the sandy units and beyond, at the surface of the grass field, and occurred in higher concentrations than in the underlying soil. Both diatom assemblages and geochemical marine proxies are indicative of tsunami inundation well beyond the sediment limit. While sea spray and associated wind cannot be totally excluded as the source of soluble salts and wind-blown diatoms, chloride concentrations do not decrease landward within the area of tsunami inundation. A decrease in chloride would have been expected if it was solely due to sea spray. While further research is required to allow us to distinguish the effects of marine inundation from sea spray, the use of geochemical proxies and diatoms provides a means to identify the limit of tsunami inundation beyond the limit of sand deposition, and as previous studies have shown, even after debris marking it have decayed. This is of importance for tsunami risk assessment and mitigation.
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    Geochemical mapping of tsunami inundation : beyond the sand
    (The Association of Applied Geochemists, 2013-11-17) Chagué-Goff, C; Wong, HKY; Goff, JR; Szczuciński, W; Gadd, PS; Cohen, DD
    Tsunami deposits range from mud to boulders, depending upon the material available for transport by these devastating waves. As sandy beaches are most often eroded, many of the reported tsunami deposits are dominated by sand, and are identified in the geological record as an anomalous sand layer within a soil or peat profile, a bit like a layer cake. However, recent posttsunami surveys have shown that the sand layer may extend up to only 60‐70% of the tsunami inundation limit, and is thus not representative of the magnitude of the event. This invariably leads to underestimates of the size of the tsunami and the generating event. As shown by the 2011 Tohoku‐oki tsunami in Japan, this can have devastating outcomes. While the inundation limit can be mapped immediately after the event using the extent of debris, salt‐burned vegetation and water marks, this evidence is often lost over time and is therefore absent in the geological record. Here we report on two studies, where the tsunami inundation limit was mapped using geochemical methods. Six months after the 2010 Maulem Tsunami in Chile, the limit of inundation was identified based on chemical and microfossil data. In Japan, geochemical markers allowed the precise limit of inundation to be identified in the absence of any sedimentological evidence. Follow‐up studies also revealed that the marine geochemical signature was preferentially preserved in the mud component of the tsunami deposit which is found inland beyond the limit of sand deposition. As no marine microfossils were recovered in this area of Japan, geochemical mapping is proving to be the only means by which tsunami inundation maps can be redrawn allowing tsunami mitigation measures to be re‐assessed.
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    Geochemical methods in studies of recent and past environmental changes
    (The Association of Applied Geochemists, 2013-11-17) Chagué-Goff, C; Wong, HKY; Gadd, PS; Cohen, DD; Cope, J
    A multi‐proxy approach is advocated in studies of recent and past environmental changes, as the use of too few diagnostic criteria often leads to misinterpretations. Geochemistry is a powerful tool which, when combined with other proxies, can provide information on short‐ and long‐term changes preserved in the sedimentary record. Geochemical methods used in the studies presented here include ion chromatography, ICPAES, ICP‐MS, portable‐XRF and X‐ray core scanning. While IC, ICP‐AES and ICP‐MS are well established techniques, P‐XRF and X‐ray core scanning have only recently been used in geosciences, particularly in Australasia. The latter, coupled with magnetic susceptibility, produces a continuous record along the length of a core with high resolution fingerprinting of environmental changes, albeit with qualitative data. Portable‐XRF is a rapid non‐destructive method, but results are semi‐quantitative. Here we discuss the application of these two methods in recent studies.Long‐ and short‐term environmental changes in Moawhitu Wetland, d’Urville Island, New Zealand, were reconstructed using a suite of multi‐proxy analyses. It was high resolution X‐ray core scanning though that provided the geochemical evidence for tsunami inundation into the wetland, beyond the extent of any sand deposit. ICP‐AES and ICP‐MS analyses of selected samples were also used to quantify and corroborate the results of the X‐ray core scanning. saltwater is more commonly used in archaeological studies, although it has recently been used to map the inundation limit following the 2011 Tohoku‐oki tsunami, and to assess the longevity of marine chemical markers in different sediment types. Concurrent analyses of waterleachable ions by IC and ICP‐AES were also used to corroborate the results of p‐XRF analysis, confirming the occurrence of saltwater indicators in the sediment.
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    Holocene record of gradual, catastrophic and human influenced environmental change at Moashitu wetland, D'Urville Island, New Zealand
    (Australian Metrological & Oceanographic Society, 2012-01-31) Cope, J; Chagué-Goff, C; Mooney, SD; Goff, JR; Zawadzki, A; Wong, HKY; Kilroy, C; Jacobsen, GE; Dominey-Howes, D
    Active tectonism, sea level fluctuation and human arrival have moulded the present day physical environment of New Zealand. Coastal wetlands are recognised archives of Holocene environmental changes. By applying sedimentological, geochemical and chronological techniques to coastal wetlands, natural and anthropogenic changes can be observed. Moawhitu Wetland, located on D’Urville Island, New Zealand, is home to a Maori oral tradition that describes a giant wave destroying a community in the 15th century. Little geological work has been carried out to investigate the evidence of the event and no studies have researched the palaeoenvironmental history of the area. This research was therefore aimed at reconstructing the Holocene environmental record at Moawhitu Wetland to determine if there was evidence of severe changes to the landscape as described in Maori oral traditions. Three sedimentary sequences from Moawhitu Wetland were used to reconstruct a 7500 year record that incorporated gradual, catastrophic and human influenced changes. The record was established by using multiple sedimentary proxies (grainsize, organic matter content, geochemistry and mineralogy) at three different sites that were temporally aligned with dating techniques (14C and 210Pb) . Barrier formation, lake and wetland formation, erosion, human influences and a tsunami ~3000-3300 yr BP were identified in the sedimentary record. These changes were applied to a broader spatial context from which inferences of sea level rise, regional faulting and potential climate change were drawn. The central west coast of New Zealand has undergone an array of short and long term environmental changes throughout the Holocene and can be identified as an area susceptible to potential tsunami events.
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    Holocene record of long- and short-term environmental changes in a coastal wetland, New Zealand
    (Geological Society of Australia, 2014-07-07) Chagué-Goff, C; Cope, J; Goff, JR; Mooney, SD; Kilroy, C; Wong, HKY; McFadgen, BG
    Long- and short-term environmental changes in Moawhitu Wetland, D’Urville Island, New Zealand, were reconstructed using a multi-proxy approach. A local Māori oral tradition describes a giant wave destroying a community in the 15th century, however, except for a study in 1962, little geological work had been carried out to investigate this event or to establish a record of paleoenvironmental changes in the area. Three sedimentary sequences sampled across the wetland over a distance of 2 km were analysed for grain size, organic content, geochemistry (ICP-AES, ICP-MS and ITRAX), diatom assemblages and mineralogy, while the chronology was obtained using 14C and 210Pb dating, corroborated with pollen biostratigraphy. Results of this study indicate that the sand dune barrier at Moawhitu formed ca 7400–7200 years BP at the time when sea levels stabilised following the last deglaciation. This led to the establishment of a freshwater lake in the southern area, which gradually infilled to form a wetland with subsequent peat accumulation. In the central part of Moawhitu, lake and peatland sequences alternated. By ca 1200 years BP, with the exception of the existing lagoon at the northern end of the study area, conditions favourable to peatland formation were found throughout Moawhitu and continued into the 20th century when they were disrupted by drainage activities. Evidence for a tsunami 3300–3000 years BP was found in the northern part of Moawhitu wetland (based on sedimentological, geochemical and microfossil data). Geochemical signatures and marine diatom assemblages provide a record of tsunami inundation in the middle part of the wetland, beyond the extent of any sand deposit. No geochemical evidence could be found at the site further inland in the southern part of the wetland. Evidence for a contemporaneous tsunami deposit has also been reported ~100 km N, on Kapiti Island, on the west coast of the North Island of New Zealand, and the event has been attributed to a local fault rupture. So far, no sedimentological, geochemical or micropaleontological evidence for a giant wave in the 15th century has been found in the sedimentary sequence of Moawhitu wetland. However, pebble layers extending across large areas of the dunes have been recorded and these have also been associated with Maori occupation, thus inferring that the sand dune may indeed have acted as an effect barrier to any 15th century tsunami. This study indicates that more than one tsunami has affected Moawhitu, and further work is planned to document environmental changes in the area. Copyright Geological Society of Australia Inc.
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    The hydrochemical response of cave drip waters to sub-annual and inter-annual climate variability, Wombeyan Caves, SE Australia
    (Elsevier, 2007-10-15) McDonald, J; Drysdale, RN; Hill, DE; Chisari, R; Wong, HKY
    A thorough understanding of cave seepage waters is necessary to interpret geochemical variations in speleothem calcite in terms of changing surface climatic conditions at a particular site. Here we present the hydrochemistry of ten cave drip waters from a karst system in SE Australia based on up to 5.5 years of monitoring. Discharge was continuously measured at six sites and manually at the other sites. Dripwater samples were analysed for pH, electrical conductivity, cations and anions at all sites at monthly or more frequent intervals. Each drip possesses a unique chemistry, and not all drip waters responded to antecedent short-term hydrological variations. For example, the hydrochemical behaviour of three adjacent drips at a bedrock depth of 45 m was completely different to that of shallower sites, and was apparently un-related to surface hydrology throughout the investigation. Based on modelled calcite precipitation vectors, prior calcite precipitation was demonstrated at several sites but can only be linked directly to changes in surface recharge at the shallowest sites. At extremely low flow, shallow drip waters accessed a high Mg, Sr and Ba source, thought to be the overlying soil. High-frequency sample collection allows for the calculation of predicted Mg/Ca-calcite and Sr/ Ca-calcite values, highlighting that the sites with the greatest potential to record high-resolution palaeohydrological records are those situated at shallow depth. Longer temporal-resolution palaeohydrological records may be recorded at deeper sites but longer-term monitoring is required to identify probable time scales. Inherent system non-linearities, dissolution of secondary calcite in pore spaces of the aquifer, changes in the source of trace elements, and the presence of multiple reservoirs confirm the need for the use of multiple speleothems and a multi-proxy approach to gain accurate palaeohydrological records from this site. © 2007, Elsevier Ltd.
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    Identification of sources and processes in a low-level radioactive waste site adjacent to landfills: groundwater hydrogeochemistry and isotopes
    (Taylor & Francis Group, 2014-11-25) Cendón, DI; Hughes, CE; Harrison, JJ; Hankin, SI; Johansen, MP; Payne, TE; Wong, HKY; Rowling, B; Vine, M; Wilsher, KL; Guinea, A; Thiruvoth, S
    Multiple tracer-element and isotope approaches were applied at a 1960s-era low-level radioactive waste burial site located in the Lucas Heights area on the southwest urban fringe of Sydney, Australia. The site is situated among other municipal and industrial (solid and liquid) waste disposal sites causing potential mixing of leachates. Local rainfall contains marine-derived major ion ratios that are modified during infiltration depending on waste interactions. The local geology favours the retention of contaminants by ion-exchange processes within the clay-rich soils and the shale layer underlying the burial site. Local soils experience periodic infiltration and wetting fronts that can fully saturate the waste trenches (bathtub effect) while surrounding soils are mostly unsaturated with discontinuous perched lenses. Within the trenches, the degradation of organic matter results in localised methanogenesis, as suggested by enriched δ2H and δ13CDIC values in adjacent subsurface water. Movement of contaminants from the trenches is indicated by Na+, Br? and I? concentrations, variations in 87Sr/86Sr, enriched δ13CDIC values and evolution of δ34S of dissolved sulfate in perched water bodies above the shale. Although transport is limited by the low transmissivity of the clay-rich soils, migration and mixing processes are indicated by the variation of concentrations with distance from the trenches, disappearance of δ2H enrichments, mixing with other sources of Sr and sulfate isotope fractionations. The depth distribution of waste-derived contaminants (specifically 3H and Be) between the perched water surrounding the trenches, and the underlying shale and sandstone layers, indicates limited downward transport of contaminants. Past removal of the shale layer in an adjacent site, Harrington's Quarry, has facilitated the mixing of some municipal waste leachates (characterised by circum-neutral pH, high alkalinity, low sulfate, high 3H, high Be, enriched δ2H and δ13CDIC) into the underlying groundwater system as suggested by high TDS, Cl?/Br? ratios, Be and 3H found in deeper wells. This study demonstrates the applicability of using trace elements, stable- and radio-isotopes to document the existing geochemistry and the contaminant transport from the waste trenches. The multiple tracer approach addresses the complexities of transport at the site and differentiates various municipal, industrial and radioactive waste sources. © 2014 Informa UK Limited