Browsing by Author "Waring, CL"

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    Cave atmosphere; a guide to calcification and a methane sink
    (Elsevier; Cambridge Publications, 2009-06-23) Waring, CL; Griffith, DWT; Wilson, SR; Hurry, S
    Studies of cave environments and speleothem growth are an important step towards quantitative speleothem palaeoclimate interpretation. Net accumulation of CaCO3 (speleothem growth) requires a perturbation to Gas-Aqueous-Solid equilibrium conditions in the cave environment (Aq. chem., T, P, pCO2). The largest equilibrium change in a ventilated cave environment causing speleothem growth is fluctuating pCO2 as a response to the cave air exchange, driven by external temperature. An intense 3-week field campaign in May 2008 (winter) using an FTIR spectrometer continuously measured (5 min) trace gases (CO2, CH4, N2O) H2O and δ13CCO2. Simultaneous drip-water pH, air flow, temperature, pressure, and relative humidity was logged by sensors in the cave together with external rainfall, temperature, pressure, and relative humidity. Drip water was sampled twice daily, coinciding with CO2 maxima and minima, for dissolved inorganic carbonate DIC, δ13CDIC, dissolved organic carbonate DOC, δ13CDOC, alkalinity, anions, and cations. Further spot samples were taken for drip-water stable isotopes, 14CDIC, and 3H. Low pCO2 in the morning cave air causes rapid speleothem growth with CO2 exsolved to the cave atmosphere lowering drip-water pH. pCO2 increases to an evening maxima and slows speleothem growth before early morning T induced ventilation decreases pCO2. δ13CCO2 has an antithetic relationship with CO2, with low pCO2 morning air the highest δ13CCO2 at -8 ‰ PDB. A Keeling analysis of end-member component mixing reveals the proportion of external air drawn into the cave and CO2 produced from speleothem formation through the diurnal cycle. Methane concentration in cave air also cycles through a diurnal pattern, negatively correlated with CO2. The methane concentration ranges from normal atmospheric 1700 ppb to <200 ppb and cycles 1000 ppb in only a few hours. Methane consumption is very rapid, suggesting a biogeochemical mechanism.
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    Cave radon exposure, dose, dynamics and mitigation
    (National Speleological Society, 2021-03) Waring, CL; Hankin, SI; Solomon, SB; Long, S; Yule, A; Blackley, R; Werczynski, S; Baker, AC
    Many caves around the world have very high concentrations of naturally occurring 222Rn that may vary dramatically with seasonal and diurnal patterns. For most caves with a variable seasonal or diurnal pattern, 222Rn concentration is driven by bi-directional convective ventilation, which responds to external temperature contrast with cave temperature. Cavers and cave workers exposed to high 222Rn have an increased risk of contracting lung cancer. The International Commission on Radiological Protection (ICRP) has re-evaluated its estimates of lung cancer risk from inhalation of radon progeny (ICRP 115) and for cave workers the risk may now (ICRP 137) be 4–6 times higher than previously recognized. Cave Guides working underground in caves with annual average 222Rn activity > 1,000 Bq m⁻3 and default ICRP assumptions (2,000 workplace hours per year, equilibrium factor F ₌ 0.4, dose conversion factor DCF ₌ 14 µSv (kBq h m⁻3)⁻1 could now receive a dose of > 20 mSv y₋1 . Using multiple gas tracers (δ13C-CO2, Rn and N2O), linked weather, source gas flux chambers, and convective air flow measurements a previous study unequivocally identified the external soil above Chifley Cave as the source of cave 222Rn. If the source of 222Rn is external to the cave, a strategy to lower cave 222Rn by passively decreasing summer pattern convective ventilation, which draws 222Rn into caves, is possible without harming the cave environment. A small net annual average temperature difference (warmer cave air) due to geothermal heat flux produces a large net annual volumetric air flow bias (2–5:1) favoring a winter ventilation pattern that flushes Rn from caves with ambient air. Rapid anthropogenic climate change over decades may heat the average annual external temperature relative to the cave temperature that is stabilized by the thermal inertia of the large rock mass. Relative external temperature increases due to climate change (Jenolan Caves, 2008–2018, 0.17°C) reduces the winter pattern air flow bias and increases Rn concentration in caves. © The Authors
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    A cost comparison of soil C measurement methods
    (Leibniz-Institute for Agricultural Engineering Potsdam-Bornim, 2013-05-26) Waring, CL; Whelan, B
    The high cost of accurately measuring soil carbon mass by soil sampling and laboratory analysis at farm scale has impeded the adoption of carbon farming methods and generation of carbon credits for soil carbon sequestration. Proximal soil sensing methods such as visible - Near Infra Red (vis-NIR) and Fast Neutron Activation Analysis (FNAA) provide a lower cost alternative to standard soil sampling. At the sample rate of 1 / ha soil sampling and laboratory analysis costs A$124 / measure, vis-NIR A$23 – A$37 / measure, and stop & go mode FNAA scanning A$2 / measure. At higher sample rates (22 / ha) with 5m long integrated samples, continuous mode FNAA scanning offers the prospect of affordable (A$0.32 / measure or A$7.27 / ha) soil carbon mapping. © 2013 International Union of Soil Sciences Working Group on Proximal Soil Sensing.
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    Discrete interval sampling investigations into the relationship between upland swamps and siltstone aquitards within the Hawkesbury Sandstone, Sydney Basin
    (Australasian Environmental Isotope Conference, 2009-12-03) Peterson, MA; Mitry, WH; Waring, CL
    The Southern Coalfields of the Sydney Basin underlie large tracts of Sydney’s water catchment area. This area comprises a dissected plateau of near-horizontal strata, typically capped by the quartzose Hawkesbury Sandstone, with dams constructed across some of the deeper valleys. Many of the perennial tributaries arise within small upland swamps of several hectares size, which exist near the watershed divides. The swamps seem to be reliant on lateral groundwater flowpaths and iron-rich basal rock bars, both of which appear to be controlled by coherent siltstone aquitards within the Hawkesbury Sandstone. Here we present some results from a baseline study of one upland swamp, comparing the swamp with samples, geology and measurements from an open borehole on an adjacent ridge. Swamps and hillslopes were sampled from surface water and piezometers; including field measurements, stable and radioisotopes and general chemistry. Discrete intervals within the nearby borehole were selected based on drill core and other logging results that inferred naturally fractured layers of higher hydraulic conductivity, separated by the siltstones and other coherent sandstones. Five selected zones were isolated, sampled and measured using ANSTO’s zone-of- interest groundwater sampler (ZOIGS). Isolation of 5 m intervals is achieved using inflatable straddle packers, with vibrating wire piezometers measuring pressures above, within and below the isolated zone. Effective isolation by the packers and the siltstone aquitards was confirmed by head differences and independent recovery curves of adjacent zones during purging and sampling. Recovery curves were also used to infer effective hydraulic conductivities for each isolated zone. Tritium, deuterium, oxygen-18 and other results show that the lower portion of the swamp, just above the outcropping siltstone layer, had a higher contribution of groundwater. Exposure of the groundwater to the atmosphere at this point causes dissolved iron to oxidise and precipitate, which hardens the basal rock bar of the swamp against nick-point erosion. The basal rock bars therefore maintain a low hydraulic gradient and perched water table within the swamps. The two significant siltstone layers in the borehole were replicated at similar elevations within the swamp and in two previous boreholes in the area, implying that they may be quite extensive. Examination of the elevations of basal and mid-swamp rockbars of over 20 swamps in the local area indicates that many coincide with the level of these two siltstone layers. The implication is that the aquitard properties of the siltstone may be responsible for both the formation and survival of the swamps. Longwall coal mining often leads to subsidence and fracturing of the strata, sometimes resulting in changes to the surface-groundwater and aquifer connectivities. Fracturing of the aquitards and/or rock bars could dewater upland swamps if mining is not managed carefully. BHP Billiton Illawarra Coal Pty Ltd supported this and other baseline studies to better understand the upland swamps before undermining proceeds.
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    Groundwater response to heavy precipitation.
    (Australian Nuclear Science and Technology Organisation, 2003-04) Waring, CL; Bradd, J; Hankin, SI
    An investigation of the groundwater response to heavy rainfall at Lucas Heights Science and Technology Centre (LHSTC) is required under the conditions of Facility Licence F0001 for the ANSTO's Replacement Research Reactor. Groundwater continuous hydrograph monitoring has been used for this purpose. Hydrograph data from four boreholes are presented showing the rainfall recorded during the same period for comparison. The drought conditions have provided only limited cases where groundwater responded to a rainfall event. The characteristic response was local caused by saturated soil contributing water directly to the borehole and the falling head as the water was redistributed into the aquifer in a few hours. Hydrograph data from borehole near the head of a gully showed that groundwater flow from the plateau to the gully produced a peak a few days after the rainfall event and that the water level returned to its original level after about 10 days. The hydrograph data are consistent with an imperfect multi-layer groundwater flow regime developed from earlier seismic and geophysical data with decreasing rate of flow in each layer due to decreasing hydraulic conductivity with depth. The contrast in hydraulic conductivity between the thin permeable soil layer and the low permeable sandstone forms an effective barrier to vertical flow.
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    How weather and climate influences speleothem growth and paleo-climate isotopic records
    (Geological Society of Australia, 2014-07-07) Waring, CL; Hankin, SI
    Speleothem growth band variations in chemical and isotopic composition are used to infer paleo-climatic conditions. Interpretation of speleothem paleoclimatic records may be improved by matching analysed subsamples to the represented elapsed time and prevailing weather or climatic conditions. Analysed subsamples may represent a month for rapid growth speleothems or many years for slow speleothem growth. Speleothem growth may also be seasonally biased affecting the paleo-climate record. To better understand the temporal fine scale of speleothem growth patterns we have principally used CO2 concentration in cave air. As CaCO3 is precipitated to accrete a new speleothem layer, CO2 is released into the atmosphere. However, CO2 may also come from other sources. To discriminate between different sources a real-time isotopic CO2 analyser, located near the entrance to Chifley Cave, is used. Cave air is sequentially sampled for 10mins from 4 internal and 2 external locations and analysed for H2O, CH4, CO2, and δ13CCO2. The 3 principal sources of CO2 are external air, speleothem growth and soil-air. The proportion of each CO2 source contributing to the total cave air CO2 is calculated for each sampled Chifley Cave location. CO2 exhaled from passing tour groups is often recorded as a minor rapid increase before subsiding to the previous background levels over 10–15 mins. Cave air CO2 shows a seasonal (summer maximum) and often a diurnal cycle, from a minimum late morning to a maximum in the late evening caused by ventilation of external low CO2 air. Differences between the external temperature and the near constant cave air temperature causes a buoyancy contrast which drives bidirectional cave air ventilation. On hot days cool cave air (11°C) sinks into the Grand Arch and is replenished by sucking external air from the Plughole cave opening. The slightly lower cave atmospheric pressure on hot days also causes soil-air rich in CO2 to seep into Chifley Cave, notably at the bottom of Katies Bower. On cold winter days relatively buoyant warm cave air escapes via the Plughole 70 m above and through minor fissures reversing the summer pattern. A detailed description (10 min sampling for 2 years) of the speleothem growth pattern in response to external temperature variation is presented.
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    Is percent ‘projected natural vegetation soil carbon’ a useful indicator of soil condition?
    (Springer, 2014-03-03) Waring, CL; Stockmann, U; Malone, BP; Whelan, B; McBratney, AB
    The concentration of Soil Organic Carbon (SOC) is often used as an indicator of soil condition and soil health. To be useful as an indicator, SOC must be considered in context, with soil type, climatic region, local rainfall, slope, and land use history influencing measured amounts of SOC. The concept of Percent Projected Natural Vegetation Soil Carbon (PNVSC) implicitly incorporates these context variables. Percent PNVSC is defined as a simple percentage comparing the contemporary measured soil carbon against a hypothetical amount of soil carbon that would be observed in the local landscape today, if the areas under managed agroecosystems remained under natural vegetation (which in this study is dry sclerophyll forest). The term ‘natural’ used in the PNVSC concept approximates with the natural system prior to agrarian settlement. Percent PNVSC was calculated for a 22,000 ha sub-catchment of the Hunter Valley, Australia and it showed a spatially weighted average of 73, indicating substantial soil carbon loss as a result of cumulative land use change over more than 100 years. The Percent PNVSC map highlights changes in soil carbon distribution across the landscape with mid-slope positions lower in the catchment showing the greatest loss of soil carbon. Viticulture has resulted in half of the original SOC being lost, compared to a 75 % PNVSC for unimproved pasture and an 83 % PNVSC for improved pasture. Average soil carbon loss due to mixed land-use change in this sub-catchment is 13,331 kg C/ha. © 2014, Springer International Publishing Switzerland.
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    An isotopic approach to hydrological mass balance in the Nattai river catchment (SE, NSW), 2. Rain, groundwater and stream sulfate 35S, δ34S, δ18O, Δ17O.
    (Centre for Groundwater Studies, 2006-12-13) Waring, CL; Lee, G; Collins, E; Hankin, SI; Cendón, DI
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    Mine subsidence induced hydraulic connection tested by geochemical and geophysical tracing techniques.
    (Mine Subsidence Technical Society, 2007-11-27) Waring, CL; Peterson, MA
    Changes in surface and groundwater hydrology induced by mine subsidence near surface fracturing can also subtly alter the geochemistry. More rapid drainage of surface and groundwater along fracture pathways may lower the standing water level allowing air to penetrate further, accelerating rock weathering and leaching reactions. However, these sulphide oxidation and carbonate dissolution reaction products are normal constituents of groundwater and their presence does not necessarily indicate an impact of mine subsidence. Changes to the groundwater recharge – discharge regime due to fracturing will also affect the age of the groundwater. Whilst the groundwater age is not a significant water quality parameter it may unambiguously distinguish changes to the hydrology, where conventional chemistry may be difficult to interpret. Mine subsidence fracturing may also cause hydraulic connection between previously isolated aquifers or ultimately between the surface and the mine. Isotopic geochemical dating (35S, 3H, 14C) and tracing (δ13C, δ2H, δ18O, δ34S) techniques are used to distinguish the origin of the groundwater and potential isolation or fracture connections. Isolated groundwater may show a dissolved gas signature similar to petroleum gas within the Bulgo Sandstone. To identify the geochemical impact of mine subsidence fracturing, pre and post mining profiles are being assembled for comparison. Groundwater age profiles also help to constrain and verify groundwater flow models. However, to produce useful 14C dates from carbon dissolved in groundwater differences between carbon species (DIC dissolved inorganic carbon, DOC dissolved organic carbon and dissolved methane / ethane) caused by interaction with siderite in the aquifer are recognised and addressed. A nuclear geophysical logging technique, Prompt Gamma Neutron Activation Analysis (PGNAA) is also used to trace the flow of an injected salt solution into fractures and into the porous and permeable sandstone surrounding the borehole. The variable distance the salt tracer moves into the porous rock under a known pressure increase (above standing water level), over a known time and tracer volume allows calculation of hydraulic conductivity at 20cm increments along the length of the borehole. If there is significant flow of the tracer into fractures and beyond the PGNAA measurement range a relative tracer movement distance is provided by the PGNAA log, rather than hydraulic conductivity. Other relevant lithological and hydraulic parameters such as porosity may be derived from measured Si, H, Cl, ±Fe, ±Al elemental abundance provided by PGNAA borehole logging. Borehole sampling of aquifer water at narrow discrete intervals for geochemical profiling requires isolating the aquifer segment or individual fracture flow from the rest of the borehole. A dual packer apparatus is used to take narrow (2, 5, 10m) discrete interval samples or measure individual fracture flows.
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    New methods of mass spectrometry based on an Electron Cyclotron Resonance ion source
    (Australian Institute of Physics, 2006-12-05) Hotchkis, MAC; Josh, M; Waring, CL; Wei, T
    We are investigating the use of multiply-charged atomic ions for measuring isotopic ratios by mass spectrometry. With multiply-charged ions, molecular interferences are reduced or eliminated, as small molecules generally cannot exist as multiply-charged ions. The Electron Cyclotron Resonance Ion Source (ECRIS) provides a highly efficient means for the production of beams of multiply-charged atomic ions [1]. We have built a compact ECRIS at ANSTO for this work. Applications include the measurement of radiocarbon in small mass samples, as an alternative to Accelerator Mass Spectrometry (AMS). In our method for radiocarbon [3], the same two principles that enable AMS to work are used, but in reverse order. Molecular interferences are eliminated in the first stage of the spectrometer system, by producing high charge state ions directly from an ECRIS. 14N interference is eliminated in the second stage, by converting the beam to negative ions in a charge exchange cell. In another application of the ECRIS, we are using it with a single magnetic sector analyser to determine stable isotopic ratios such as 13C/12C and 18O/16O. Measurements of these and other stable isotopes are widely used in geo- and bio-sciences, where either natural variations are studied or isotopic tracers are used. Conventional isotope ratio mass spectrometers use molecular ions (such as CO2+) to determine such ratios. In our method, 2+ atomic ions are selected, thereby eliminating possible molecular interferences and resolving mass ambiguities that exist with the conventional molecular ion method. [1] R. Geller, Electron Cyclotron Resonance Ion Sources and ECR Plasmas, IOP, Bristol, 1996. [2] R. Middleton, in Proc. First Conf. on Radiocarbon Dating with Accelerators, H.E. Gove (ed.), Rochester, USA, 1978. [3] M.A.C. Hotchkis and T. Wei, 10th International Conference on AMS, Sept 5-10 2005, Berkeley, USA.
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    Seasonal total methane depletion in limestone caves
    (Springer Nature, 2017-08-16) Waring, CL; Hankin, SI; Griffith, DWT; Kertesz, MA; Kobylski, V; Wilson, NL; Coleman, NV; Kettlewell, G; Zlot, R; Bosse, M; Bell, G
    Methane concentration in caves is commonly much lower than the external atmosphere, yet the cave CH4 depletion causal mechanism is contested and dynamic links to external diurnal and seasonal temperature cycles unknown. Here, we report a continuous 3-year record of cave methane and other trace gases in Jenolan Caves, Australia which shows a seasonal cycle of extreme CH4 depletion, from ambient ~1,775 ppb to near zero during summer and to ~800 ppb in winter. Methanotrophic bacteria, some newly-discovered, rapidly consume methane on cave surfaces and in external karst soils with lifetimes in the cave of a few hours. Extreme bacterial selection due to the absence of alternate carbon sources for growth in the cave environment has resulted in an extremely high proportion 2–12% of methanotrophs in the total bacteria present. Unexpected seasonal bias in our cave CH4 depletion record is explained by a three-step process involving methanotrophy in aerobic karst soil above the cave, summer transport of soil-gas into the cave through epikarst, followed by further cave CH4 depletion. Disentangling cause and effect of cave gas variations by tracing sources and sinks has identified seasonal speleothem growth bias, with implied palaeo-climate record bias. © 2017, The Author(s)
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    Use of multiply charged atomic ions for isotope ratio mass spectrometry
    (Wiley-Blackwell, 2008-05) Hotchkis, MAC; Button, D; Waring, CL
    We have investigated the use of multiply charged atomic ions for the measurement of isotopic ratios of gaseous and vapour samples. We use a mass spectrometer system incorporating an electron cyclotron resonance (ECR) ion source for this purpose. In the cases of carbon, nitrogen and oxygen, the selection of the 2+ atomic species is found to be the most effective for obtaining reliable isotopic ratios. Using samples of carbon dioxide, nitrogen, air and water vapour, we have demonstrated the determination of the isotopic ratios C-13/C-12, N-15/N-14, O-17/O-16 and O-18/O-16. For oxygen, this technique offers an alternative to the equilibration or purification methods normally required to obtain isotopic ratios of water or other oxygen-containing samples. In particular, O-17/O-16 can be measured directly without isobaric interference from OH+. With typical ionization efficiencies of greater than 10%, ECR ion sources have the potential to enable measurements on very small samples. In addition to those evaluated in the present work, there is scope for application of this method to other sample types, to a variety of sampling methods, and to other elements. © 2008, Wiley-Blackwell.
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    Use of stable isotopes in Sydney catchment process and water quality studies
    (Australian Water Association and Waste Management Association of Australia, 2006-07-30) Hughes, CE; Mazumder, D; Gibson, JJ; Szymczak, R; Cendón, DI; Hollins, SE; Waring, CL
    The use of stable and radioactive isotopes as environmental tracers is becoming more widespread as isotopic analysis techniques become more accessible. ANSTO’s Isotopes for Water Project aims to increase awareness of the potential uses of isotopes in the management of catchments, rivers, reservoirs, aquifers, estuaries and biota. This paper outlines a range of potential applications using a wide range of isotopes (δ18O, δ2H, 14C, δ13C, δ15N, 3H, 7Be, 210Pb, 35S, δ34S, δ18O and Δ17O) in hydrology, hydrogeology, ecology and contaminant geochemistry with examples from the Sydney basin. The studies being undertaken by ANSTO include: • application of stable water isotopes to catchment and reservoir water balance; • age dating of groundwater to underpin sustainability assessment; • tracing the source of contaminants and nutrients such as nitrogen, organic matter and sulfate in catchments and waterways; • quantifying contaminated sediment dynamics and contaminant uptake into biota using shorted-lived radioisotopes; • tracing trophic linkages in aquatic food webs.
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    Using the 14C bomb pulse to date young speleothems
    (University of Arizona, 2011-04-01) Hodge, E; McDonald, J; Fischer, MJ; Redwood, D; Hua, Q; Levchenko, VA; Drysdale, RN; Waring, CL; Fink, D
    Many factors may influence the radiocarbon age results of lacustrine sediments, among which the hardwater effect is particularly important. Daihai Lake is a closed lake located in the semi-arid region of Inner Mongolia, China. High concentrations of (HCO3)- and (CO3)2- and high pH values in the lake water imply that there is a hardwater effect when using bulk lacustrine sediment samples for 14C dating. To correct the apparent 14C age, we present a pilot study based on a series of 14C ages of lake surface sediment, lake water, submerged aquatic plant (Myriophyllum), fish bone (Cyprinus carpio), and surface soil samples from and around Daihai Lake. Assuming that the relationship between the 14C/12C ratio of DIC and of atmospheric CO2 was constant (at 0.816), the hardwater effect ages calculated for the past 8000 yr would have varied from 949 to 1788 yr. Together with the reservoir effect and soil organic matter input, the hardwater effect is a major factor causing changes in apparent age when using bulk organic matter for 14C dating. © 2011, University of Arizona.