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Stability and storage of soil organic carbon in a heavy-textured Karst soil from south-eastern Australia
No full textBoth aggregation and mineral association have been previously found to enhance soil organic carbon (SOC) storage (the amount of organic C retained in a soil), and stability (the length of time organic C is retained in a soil). These mechanisms are therefore attractive targets for soil C sequestration. In this study, we investigate and compare SOC storage and stability of SOC associated with fine minerals and stored within aggregates using a combination of particle-size fractionation, elemental analysis and radiocarbon dating. In this heavy-textured, highly aggregated soil, SOC was found to be preferentially associated with fine minerals throughout the soil profile. By contrast, the oldest SOC was located in the coarsest, most highly aggregated fraction. In the topsoil, radiocarbon ages of the aggregate-associated SOC indicate retention times in the order of centuries. Below the topsoil, retention times of aggregate-SOC are in the order of millennia. Throughout the soil profile, radiocarbon dates indicate an enhanced stability in the order of centuries compared with the fine mineral fraction. Despite this, the radiocarbon ages of the mineral-associated SOC were in the order of centuries to millennia in the subsoil (30–100 cm), indicating that mineral-association is also an effective stabilisation mechanism in this subsoil. Our results indicate that enhanced SOC storage does not equate to enhanced SOC stability, which is an important consideration for sequestration schemes targeting both the amount and longevity of soil carbon. © 2014 CSIRO Publishin
Self-assembly of a unique 3d/4f heterometallic square prismatic box-like coordination cage
No full textAbstractWe present the synthesis and characterization of a unique, slightly distorted square prismatic, box-like coordination cage of type [Cu6Dy8L8(MeOH)8(H2O)6](NO3)12·χsolvent obtained via the supramolecular assembly between a non-centrosymmetric Dy(III) metalloligand and Cu(II) nitrate. Magnetic susceptibility measurements indicate that the complex behaves as a single-molecule magnet. © 2016 Royal Society of Chemistr
Computational studies on hypervalent iodonium(III) compounds as activated precursors for 18F radiofluorination of electron-rich arenes
No full textFluorination of deactivated and non-activated electron-rich arenes via nucleophilic aromatic substitution (SNAr) reactions represents a major challenge in medicinal and radiochemistry. In efforts to activate electron-rich arenes for facile synthesis of fluoroarenes, a wide range of reagents have been developed. In particular, aryliodonium(III) species (salts and ylides) show promise as reagents for synthesising 18F-radiolabelled molecules for use in positron emission tomography (PET). However, in fluorination reactions involving a reductive elimination mechanism, aryliodonium(III) reagents present two competing pathways that lead to product (via transition state 1 (TS1)) or by-product (TS2) formation. Here, we present detailed computational studies using Density Functional Theory (DFT) methods on the relatively stability of these competing transition states and present an analysis based on transition state theory that allows prediction of chemoselectivity in aryliodonium(III) fluorination reactions. The methods developed indicate that the calculated difference in free energy (ΔΔG‡) and the calculated equilibrium constant (ln K‡) between the two transition states are chemically accurate molecular descriptors of chemoselectivity in aryliodonium(III) fluorination. It is anticipated that the tools developed here will aid design of the next generation of reagents with increased chemoselectivity for fluorination and radiofluorination of electron-rich arenes. © 2015 Elsevier B.V
Ten trenches: A science-art collaboration
No full textCollaborative and cross-disciplinary research by a group of artists and scientists in an Australian rural setting generates data and ideas that form the basis of a wider understanding of the ramifications of global warming and cooling within the local, regional and national community. The work is viewed as an initial educational platform that will allow the public to see and understand the complexities of climate-based research. © 2020 The MIT Pres
Sustainability of groundware under climate change
No full textOne of the key commitments from the plan of implementation of the World Summit on Sustainable Development Johannesburg 2002 was to 'develop integrated water resources management and water efficiency plans by 2005'. In this paper, a detailed concept will be presented for assessing the sustainability of groundwater in warm arid and semi-arid areas challenged by climate change. The IAEA Global Network of Isotope Precipitation (GNIP) database is fundamental to the development of the concept which will be extended to the evaluation of climate change models. The concept will be evaluated with data from three recharge areas in the Great Artesian Basin, as well as aquifers in Central Australia, in the far north of the country and in Victoria. Experimental work is currently being extended to the Murray-Darling Basin. The role of the GNIP in the evaluation of climate change models is illustrated with data from the Amazon. Groundwater sustainability is achieved through balancing exploitation of the resource with recharge. As groundwater exploitation raises issues of demand management beyond the scope of this paper, the focus will be on recharge. Surface water infiltration is dependent on total rainfall within the intake areas, the seasonal distribution of rainfall, the rainfall intensity and the antecedent landscape conditions. Variation in total rainfall can be predicted without recourse to isotope data. However, effective recharge will only occur if the total monthly rainfall exceeds a threshold value. The above-mentioned concept involves predicting these threshold values from GNIP and groundwater isotope data. The evaluation of the concept with field data, and its incorporation into a predictive tool are the central themes of this paper. Four stages are involved: Stage 1: Correlating isotope depletion and the total monthly rainfall Analysis of the GNIP data from continental stations shows a widespread trend towards increasing stable isotope depletion with increasing monthly average rainfall. Stage 2: Matching stable isotope levels in groundwater with those in rainfall with monthly totals exceeding a threshold value The stable isotope levels in groundwater is generally depleted relative to that in mean average rainfall at recharge. The groundwater levels match those in rainfall provided the monthly intensity reaches a threshold value. This value, which may be expressed as a percentile of all monthly data for the GNIP station, is interpreted as the threshold value for effective recharge. The difference between the stable isotope ratios in groundwater and in the mean rainfall is called the 'groundwater depletion'. Stage 3: Correlating the 'groundwater depletion' with aridity. It will be shown with reference to data from Australian aquifers that the 'groundwater depletion' correlates with a defined 'aridity index'. Stage 4: Development of the predictive tool: The above mentioned correlation is the basis of a tool which may be applied to a) assessing groundwater sustainability, b) predicting soil moisture in the root zone and thus contribute to agricultural sustainability and c) evaluating climate change models. a) Groundwater sustainability: Climate change leads to variations in the 'aridity index' and hence to variations in the threshold intensity for effective recharge (Stage 3 above). Climate changes may be modelled numerically, assessed through correlations with sub-global parameters such as ENSO (El Nino Southern Oscillation) Index or simply postulated as scenarios. Reliable knowledge of predicted changes to effective recharge, would provide decision makers with additional time to adjust the groundwater exploitation rate consistent with the long term sustainability of the resource. b) Sustainability of the agricultural and pastoral industries: Variations in soil productivity depend on a number of factors including moisture levels in the root zone. Predictions of the soil moisture levels will depend on the temporal variation of the effective recharge (above), the water balance and the residence time distribution of the water. The use of isotopes to establish a water balance at a site in the Darling basin has been demonstrated. c) Evaluation of climate models: The use of isotopes to evaluate climate change models has been demonstrated in the Amazon basin. The principles will be extended to arid and semi arid areas using isotopic data in age dated groundwater as a probe for variations in effective recharge and therefore in the aridity index. The concept will be illustrated with data from the Great Artesian Basin and the Mereenie Sandstone aquifer in Central Australia. On-going project work will be focussed on ANSTO's contribution to the Murray-Darling Water Basin Study through the GEWEX (Global Energy and Water Cycle Experiment) Hydrometeorological Panel and the IAEA Coordinated Research Program Isotope Tracing of Hydrological Processes in Large River Basins, 2002-2004. The Organisation is also contributing to the Integrated Climate System Study (ICSYS) initiative of the IAEA/WCRP (World Climate Research Programme). © The authors
Preliminary design and cost considerations for a plant to produce nuclear purity uranium dioxide from Australian ore concentrates
No full textDesign considerations are outlined for plants for the production of nuclear purity uranium dioxide with capacities of 100, 200 and 500 tonnes U/year. The cost of the process equipment is not greatly affected by various process alternatives; equipment performance, which affects product quality, consistency of power properties and plant reliability, is important in determining the recommended process. This involves the following steps: batch dissolution, continuous solvent extraction in mixer-settlers, single-stage precipitation of ADU, thickening and spray drying of ADU, and calcination-reduction in continuous pulsed fluidised bed reactors. Estimates of the cost of recovery of free acid and combined nitrate from the raffinate and filtrate waste streams indicated that the value of the recovered acid would be greater that the processing cost only in the case of free acid recovery from solvent extraction raffinate in the 500 tonne/year plant. However if acid recovery is necessary for plant effluent control, the processing cost can be largely offset by the value of the recovered acid
Investigation ofδ18Oandδ2Hin the Namoi River catchment—elucidating recharge sources and the extent of sur-face water/groundwater interaction
Get PDFStable isotopes 18O and 2H were analysed in water samples from rainfall, surface water and groundwater within the semi-arid Namoi River catchment in NSW, Australia.The isotopic composition of rainfall events and groundwater samples plot along the Local Meteoric Water Line (LMWL). In contrast, the surface water samples of the Namoi River clearly show signs of evaporative enrichment and plot on a Local Evaporation Line (LEL) constructed for the area based on δ18O and δ2H time-series for surface waters of the Namoi River. The river samples have a distinctly lower slope than the LMWL which is due to evaporation. Shallow groundwater near the Namoi River shows considerable enrichment compared to average groundwater signatures and plots in between the LMWL and the LEL on a δ2H vs. δ18O graph. These results clearly indicate that the Namoi River is recharging the shallow aquifer system. Conversely, the isotopic composition of surface water in the tributaries of Maules and Horsearm creeks are similar to groundwater indicating that these creeks are receiving groundwater discharge. This study reveals many complex hydrological processes occurring in the catchment. It would not have been possible to elucidate these processes without the use of stable isotope data
Estimating diffusion in heterogeneous groundwater systems using short-llived radio-isotopes and stable isotopes or bromine
No full textDiffusion 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
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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 In
Radiation protection and regulation for environmental radiotracer studies
No full textThe use of radioactive tracers in the environment is subject to national regulation as well as International Standards and Guidelines. These address aspects of radiation protection during transport, deployment and in the environment following deployment and are relevant not only to radiation workers and members of the public, but also to non-human biota in the receiving environment. This paper outlines the regulatory framework and safety aspects relating to radiotracing and provides examples of radiation doses modeling for humans and non-human biota. © The authors.International Atomic Energy Agenc
