Browsing by Author "Hughes, CE"
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- Item131I discharges to the marine environment and uptake by algae in Sydney, Australia(South Pacific Radioactivity Association, 2008-11-25) Veliscek-Carolan, J; Hughes, CE; Hoffmann, EL; Loosz, TThe use of radiopharmaceuticals in nuclear medicine results in radioactive material being discharged to the sewer as human waste. Treated sewage effluent is in turn discharged to the marine environment through coastal and deepwater outfalls. 131l is the dominant medical isotope discharged to the environment as treatment doses can be large (up to 8 GBq) and excretion from patients is rapid. Also, 131l has a half life (8.04 days), which is significantly greater than the effluent residence time in the sewerage system (< 1 day), and a low Kd resulting in a low removal during treatment. 131l levels from <1 to 150 Bq/L have been measured in effluent from Sydney sewage treatment plants. Following discharge of effluent to ocean outfalls, 131l levels in the seawater are likely to be low as a result of dispersion and dilution of the effluent. However, 131I is easily detected in macroalgae growing near coastal outfalls as the algae bio-accumulate iodine. In fact, 131I levels between 1 and 375 Bq/kg have been observed in various macroalgae species near the outfall from Cronulla sewage treatment plant in Sydney, since November 1995. This paper presents data on 131l levels in effluent and uptake by algae growing near shoreline outfalls in the Sydney region. Radiation doses to marine biota from 131l discharged to coastal waters are calculated to be very small and below the ERICA screening level of l0 uGy/hr. Human dose assessment is also discussed.
- Item99mTc vs Rhodamine WT for tracing coastal hydrodynamics(Tous droits réservés., 2014-10-13) Hughes, CE; Patterson, RGRhodamine WT is a tracer commonly used to quantitatively and visibly trace currents and contaminant plumes. Radioactive tracer 99mTc can also be used for these applications. Both of these tracers were injected simultaneously in a study of currents in a nearshore area of Darwin Harbour, Australia. Five subsurface drifters were released at one minute intervals during the tracer releases as an additional method of determining dispersive processes. Aerial photography was used to observe the Rhodamine WT plume. These methodologies provided data on dispersion and advection for calibration of a 2D hydrodynamic model of the harbour, which was in turn used to design the extension of a sewage outfall. Using this case study we contrast and compare the independent analysis of the two tracer methods. Some differences in the initial tracer plume are expected due to different deployment methods. Differences in detection systems may lead to time lags between datasets. The methods used to quantify tracer concentration will also be discussed. Once these technical aspects are accounted for it should be possible to directly compare the behaviour of the two tracers and their suitability for determining dispersion. Logistical aspects relating to tracer availability, detection systems, human safety, environmental impact and cost will also be addressed. Unexpected regulatory obstacles existed for Rhodamine WT – a tracer specifically designed for surface water and 99mTc was the favoured tracer out of the two for regulators in the Northern Territory of Australia on the basis of environmental impact.
- ItemAccelerator mass spectrometry measurements of 233U in groundwater, soil and vegetation at a legacy radioactive waste site(Elsevier, 2024-06) Payne, TE; Harrison, JJ; Child, DP; Hankin, SI; Hotchkis, MAC; Hughes, CE; Johansen, MP; Thiruvoth, S; Wilsher, KLLow-level radioactive wastes were disposed at the Little Forest Legacy Site (LFLS) near Sydney, Australia between 1960 and 1968. According to the disposal records, 233U contributes a significant portion of the inventory of actinide activity buried in the LFLS trenches. Although the presence of 233U in environmental samples from LFLS has been previously inferred from alpha-spectrometry measurements, it has been difficult to quantify because the 33U and 234U α-peaks are superimposed. Therefore, the amounts of 233U in groundwaters, soils and vegetation from the vicinity of the LFLS were measured using accelerator mass spectrometry (AMS). The AMS results show the presence of 233U in numerous environmental samples, particularly those obtained within, and in the immediate vicinity of, the trenched area. There is evidence for dispersion of 233U in groundwater (possibly mobilised by co-disposed organic liquids), and the data also suggest other sources of 233U contamination in addition to the trench wastes. These may include leakages and spills from waste drums as well as waste burnings, which also occurred at the site. The AMS results confirm the historic information regarding disposal of 233U in the LFLS trenches. The AMS technique has been valuable to ascertain the distribution and environmental behaviour of 233U at the LFLS and the results demonstrate the applicability of AMS for evaluating contamination of 233U at other radioactive waste sites. © 2024 Australian Nuclear Science and Technology Organisation. Published by Elsevier Ltd. This is an open access article under the CC BY license
- ItemAlternative least squares methods for determining the meteoric water line, demonstrated using GNIP data(Elsevier, 2014-11-01) Crawford, J; Hughes, CE; Lykoudis, SThe relationship between δ2H and δ18O in precipitation at a site, known as the local meteoric water line (LMWL), is normally defined using an ordinary least squares regression (OLSR). However, it has been argued that this form of minimisation is more appropriate when a predictive model is being developed (and there are no measurement errors associated with the independent variable) and that orthogonal regression, also known as major axis regression (MA), or reduced major axis regression (RMA) may be better suited when a relationship is being sought between two variables which are related by underlying physical processes. The slope of the LMWLs for the GNIP data is examined using the three linear regressions, and the corresponding precipitation weighted regressions. The MA and RMA regressions generally produced larger slopes, with the largest differences for oceanic islands and coastal sites. The difference between the various methods was the least for continental sites. In all considered cases, both for the standard and precipitation weighted regressions, the slope produced by RMA was in between those determined by OLSR and MA, with OLSR producing the smaller slope. Further, the results of both RMA and precipitation weighted RMA were less sensitive to the removal of outliers and values with high leverage statistic. The results indicate that when a good linear relationship exists between δ2H and δ18O, all considered regressions result in a close fit. When the values are distributed within circles or ellipses on the δ18O–δ2H bivariate plot, as would appear in coastal and oceanic sites from first stage rainout, care needs to be taken as to which regression is utilised. However, in some of these cases, it appears the precipitation weighted MA (and in some cases MA) produces large slopes. In these cases the average Root Mean Sum of Squared Error (rmSSEav) value of the fit can be used as a guide of the suitability of the MA and PWMA for each site. Where the slope of the PWRMA was significantly different to the slope of the OLSR regression (22% of sites; dominated by coastal, island and Mediterranean locations), we believe PWRMA is more suitable.© 2014 Elsevier B.V.
- ItemApplication of environmental isotopes of hydrogen (3H), Carbon (13C & 14C) and oxygen (16O/18O) in studies of groundwater-streamflow interactions(International Atomic Energy Agency, 2006) Stone, DJM; Jacobsen, GE; Hughes, CE; Szymczak, RA current major effort in Australian water management is the conjunctive management of hydraulically connected Groundwater and Surface water systems, to provide the maximum benefit to water stakeholders. In particular Australia has a legislative limit on the amount of surface water that can be utilised in a particular catchment, but that is not the case for Groundwater, leading to tension amongst users in connected systems. Valley and Murray-Darling Basin, NSW. Streamflow was sampled using a plastic bailer while groundwaters were withdrawn with the use of a Grundfos MP1 environmental sampling pump. They were analysed for stable isotopes ({sup 2}H/H, {sup 18}O/{sup 16}O) ratios, tritium ({sup 3}H), radiocarbon ({sup 14}C) and major and minor chemical species. Rainwaters were collected and analysed for stable isotopes only. Previous tritium in precipitation data were also utilised. Ion Chromatography was used for the analysis of the anions while either ICP-MS or ICP-AES was used for cations. The tritium analysis was carried out by standard procedures of electrolytic concentration and liquid scintillation counting. Analysis of the water samples for deuterium was conducted by CSIRO, Isotope Analysis laboratory using the zinc reduction method and a VG Isogas mass spectrometer (error; {+-} 0.8 per mille). Radiocarbon in groundwaters are measured using accelerator mass spectrometry (AMS). The water samples are filtered to 45 {mu}m prior to CO{sub 2} collection. Dissolved inorganic carbon (DIC) is separated by acidifying the water samples with 85% phosphoric acid, the resulting CO{sub 2} is collected by sparging with He for 15 mins and cryogenic trapping. The CO{sub 2} is purified by heating overnight to 600 deg. C in the presence of Ag wire. Graphite targets are then prepared by the reduction of the CO{sub 2} using H{sub 2} with an Fe catalyst at 600 deg. C. The resulting graphite/iron mix is measured in the ANTARES 10MV Tandem Accelerator. The determination of oxygen-18 was conducted at the University of Wollongong using the CO{sub 2} gas equilibration method, purified using a Micromass Multiprep Unit and measured on a Micromass Prism III (error; {+-} 0.1 per mille). A plot of tritium activity versus borehole location and depth, indicates that the Brogo River (Bega Valley, NSW) is not recharging the adjacent alluvium since the tritium is much lower than in the streamwater. The Bega river however is recharging the adjacent alluvium, both above and below its confluence with the Brogo river, since tritium values are similar in stream and alluvium. Isotopes such as the stable and radioactive isotopes of water and carbon are particularly appropriate for the study of these connected water systems, providing a clear method of determining the source of groundwater, and hence the extent of mixing of nearby surface water (such as the local river), and the time frame for the mixing process. In particular the stable isotopes 2-H, 18-O, and 13-C provide a robust end-member analysis for the hydrographic separation of regional groundwater and any amount of river water which was replenished at a remote location; while the radioactive isotopes 3-H and 14-C are used to confirm the presence in groundwater of (isotopically modern) surface water, but also accurately determine the apparent rate of mixing at particular distances from the river. © The Authors
- ItemApplication of environmental isotopes of hydrogen (3H), Carbon (13C & 14C) and oxygen (16O/18O) in studies of groundwater-streamflow interactions(International Atomic Energy Agency, 2004-10-25) Stone, DJM; Jacobsen, GE; Hughes, CE; Szymczak, RA current major effort in Australian water management is the conjunctive management of hydraulically connected Groundwater and Surface water systems, to provide the maximum benefit to water stakeholders. In particular Australia has a legislative limit on the amount of surface water that can be utilised in a particular catchment, but that is not the case for Groundwater, leading to tension amongst users in connected systems. Valley and Murray-Darling Basin, NSW. Streamflow was sampled using a plastic bailer while groundwaters were withdrawn with the use of a Grundfos MP1 environmental sampling pump. They were analysed for stable isotopes ({sup 2}H/H, {sup 18}O/{sup 16}O) ratios, tritium ({sup 3}H), radiocarbon ({sup 14}C) and major and minor chemical species. Rainwaters were collected and analysed for stable isotopes only. Previous tritium in precipitation data were also utilised. Ion Chromatography was used for the analysis of the anions while either ICP-MS or ICP-AES was used for cations. The tritium analysis was carried out by standard procedures of electrolytic concentration and liquid scintillation counting. Analysis of the water samples for deuterium was conducted by CSIRO, Isotope Analysis laboratory using the zinc reduction method and a VG Isogas mass spectrometer (error; {+-} 0.8 per mille). Radiocarbon in groundwaters are measured using accelerator mass spectrometry (AMS). The water samples are filtered to 45 {mu}m prior to CO{sub 2} collection. Dissolved inorganic carbon (DIC) is separated by acidifying the water samples with 85% phosphoric acid, the resulting CO{sub 2} is collected by sparging with He for 15 mins and cryogenic trapping. The CO{sub 2} is purified by heating overnight to 600 deg. C in the presence of Ag wire. Graphite targets are then prepared by the reduction of the CO{sub 2} using H{sub 2} with an Fe catalyst at 600 deg. C. The resulting graphite/iron mix is measured in the ANTARES 10MV Tandem Accelerator. The determination of oxygen-18 was conducted at the University of Wollongong using the CO{sub 2} gas equilibration method, purified using a Micromass Multiprep Unit and measured on a Micromass Prism III (error; {+-} 0.1 per mille). A plot of tritium activity versus borehole location and depth, indicates that the Brogo River (Bega Valley, NSW) is not recharging the adjacent alluvium since the tritium is much lower than in the streamwater. The Bega river however is recharging the adjacent alluvium, both above and below its confluence with the Brogo river, since tritium values are similar in stream and alluvium. Isotopes such as the stable and radioactive isotopes of water and carbon are particularly appropriate for the study of these connected water systems, providing a clear method of determining the source of groundwater, and hence the extent of mixing of nearby surface water (such as the local river), and the time frame for the mixing process. In particular the stable isotopes 2-H, 18-O, and 13-C provide a robust end-member analysis for the hydrographic separation of regional groundwater and any amount of river water which was replenished at a remote location; while the radioactive isotopes 3-H and 14-C are used to confirm the presence in groundwater of (isotopically modern) surface water, but also accurately determine the apparent rate of mixing at particular distances from the river. © The Authors
- ItemApplication of the pore water stable isotope method and hydrogeological approaches to characterise a wetland system(Copernicus Publications, 2018-12-06) David, K; Timms, W; Hughes, CE; Crawford, J; McGeeney, DThree naturally intact wetland systems (swamps) were characterised based on sediment cores, analysis of surface water, swamp groundwater, regional groundwater and pore water stable isotopes. These swamps are classified as temperate highland peat swamps on sandstone (THPSS) and in Australia they are listed as threatened endangered ecological communities under state and federal legislation. This study applies the stable isotope direct vapour equilibration method in a wetland, aiming at quantification of the contributions of evaporation, rainfall and groundwater to swamp water balance. This technique potentially enables understanding of the depth of evaporative losses and the relative importance of groundwater flow within the swamp environment without the need for intrusive piezometer installation at multiple locations and depths. Additional advantages of the stable isotope direct vapour equilibration technique include detailed spatial and vertical depth profiles of δ18O and δ2H, with good accuracy comparable to other physical and chemical extraction methods. Depletion of δ18O and δ2H in pore water with increasing depth (to around 40–60 cm depth) was observed in two swamps but remained uniform with depth in the third swamp. Within the upper surficial zone, the measurements respond to seasonal trends and are subject to evaporation in the capillary zone. Below this depth the pore water δ18O and δ2H signature approaches that of regional groundwater, indicating lateral groundwater contribution. Significant differences were found in stable pore water isotope samples collected after the dry weather period compared to wet periods where recharge of depleted rainfall (with low δ18O and δ2H values) was apparent. The organic-rich soil in the upper 40 to 60 cm retains significant saturation following precipitation events and maintains moisture necessary for ecosystem functioning. An important finding for wetland and ecosystem response to changing swamp groundwater conditions (and potential ground movement) is that basal sands are observed to underlay these swamps, allowing relatively rapid drainage at the base of the swamp and lateral groundwater contribution. Based on the novel stable isotope direct vapour equilibration analysis of swamp sediment, our study identified the following important processes: rapid infiltration of rainfall to the water table with longer retention of moisture in the upper 40–60 cm and lateral groundwater flow contribution at the base. This study also found that evaporation estimated using the stable isotope direct vapour equilibration method is more realistic compared to reference evapotranspiration (ET). Importantly, if swamp discharge data were available in combination with pore water isotope profiles, an appropriate transpiration rate could be determined for these swamps. Based on the results, the groundwater contribution to the swamp is a significant and perhaps dominant component of the water balance. Our methods could complement other monitoring studies and numerical water balance models to improve prediction of the hydrological response of the swamp to changes in water conditions due to natural or anthropogenic influences. © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License.
- ItemApplications and impact of radiotracers and nucleonic measurement systems for investigation of sediment transport(American Nuclear Society, 2014-08-28) Bandeira, JV; Salim, LH; Brisset, P; Hughes, CENot available.
- ItemArtificial radiotracer applications in aquatic environment(International Atomic Energy Agency, 2015-01-01) Bandeira, JV; Hughes, CEThe use of artificial radiotracers in the environment is analogous to their use in the human body. In both domains they provide data on flow rates and pathways, on exchange with materials and on their final discharge from the studied system. Artificially injected radiotracers have been used to investigate flow in natural waters since the 1950's. Identification of flow paths, diagnosis of blockages or leakage, measurement of flow rates, dispersion and exchange processes, such as biological uptake or sorption, are all aspects to which a wide range of artificial radioactive tracers have been applied. Increasingly radiotracers are used in combination with numerical modelling to improve confidence in the predictive capacity of models used in the management of our water resources and to extend their spatial applicability. In turn this allows us to use less and less tracer and demonstrate that the human and environmental impact of modern radiotracer studies is minimal. © The authors.
- ItemAssessment of radionuclide distributions at an Australian legacy radioactive waste site(South Pacific Radioactivity Association, 2010-09-01) Payne, TE; Cendón, DI; Collins, RN; Dore, M; Hankin, SI; Harrison, JJ; Hughes, CE; Johansen, MP; Thiruvoth, S; Twining, JR; Wilsher, KLDuring the 1960s, low level radioactive waste was buried in shallow trenches at a disposal site in south-eastern Australia, known as the Little Forest Burial Ground. This paper discusses preliminary findings of research into the distribution of radionuclides at the site, including soils, groundwater and biota. In particular, we are studying the mobility of radionuclides; and their uptake by plants, insects and small animals. Groundwater monitoring indicates that there has been limited movement of radioactivity, other than a tritium plume that extends at least 100 m. The tritium results are being used to define the groundwater flowpaths, and the effects of seasonal and climatic factors. The pattern of tritium distribution suggests that the source of tritium is predominantly within the waste materials. However, tritium derived from a nearby municipal landfill contributes to tritium concentrations in some groundwaters, with smaller amounts from cosmogenic tritium and atmospheric deposition originating from the nearby HIFAR reactor (shut down in 2007). The tritium data provide a record of water movement against which the relative mobility of other radionuclides can be assessed. There are measurable amounts of 60Co, 90Sr, 137Cs and traces of actinides in some soils, groundwater and vegetation samples taken in close proximity to the disposal area. Isotopic ratios such as δ13C, δ180, δ2H, δ34S and 87Sr/86Sr are being measured in groundwater, in addition to the radioactive isotopes originating from the disposed wastes. Synchrotron EXAFS and XANES studies are being applied to study elemental chemical environments and oxidation states in the soils at the site. We have recently undertaken a major geophysical investigation and drilling program; and installation of an improved array of water sampling boreholes is planned. Therefore, many more samples of groundwater and soils are becoming available for analysis.
- ItemAssessment of radionuclide movement at an Australian legacy radioactive waste site(EMSL, 2009-09-20) Payne, TE; Cendón, DI; Collins, RN; Hankin, SI; Harrison, JJ; Hughes, CE; Johansen, MP; Twining, JR; Waite, TDNot available
- ItemAustralian rainfall isotope variability and its relationship with groundwater(Copernicus Publications, 2017-07-10) Hughes, CE; Crawford, J; Cendón, DI; Meredith, KT; Hollins, SERainfall stable isotope composition varies dramatically across the Australian continent. Using monthly deuterium and oxygen-18 data from 15 Global Network of Isotopes in Precipitation (GNIP), sites the underlying causes for the spatial and temporal variability have been investigated. Because of the island nature of Australia, moisture originates from the Indian Ocean to the west and the Pacific Ocean to the east, and is dominated by the monsoon and tropical cyclones to the north and frontal and low pressure systems to the south. Simple rainfall amount or temperature relationships don’t explain what is observed over this low-elevation continent because of the huge spatial variability in moisture source and synoptic processes. However, latitude, elevation and continentality were found to have some influence on the isotopic average at the 15 sites. Using relationships developed with data from the 15 GNIP sites and additional data from higher elevation sites, an isoscape has been developed. This is used to investigate what drives groundwater recharge at a variety of locations across Australia. In many regions groundwater recharge can be linked isotopically to extreme high rainfall events such as tropical cyclones, east coast lows or major troughs which may occur on sub-annual or decadal time scales. For many inland sites, recharge from such events results from widespread flooding over hundreds or thousands of kilometers, introducing an evaporated signature to the groundwater, or one that reflects a different composition to local rainfall. In contrast, reliable seasonal rainfall from the monsoon in the north, or winter rainfall in the south west leads to groundwater signatures in alluvial, karst and fractured rock aquifers that reflect wet season averages. A better understanding of how these processes vary across the continent improves our ability to apply stable isotopes to trace groundwater recharge and ultimately provides valuable information for water resource managers to understand the sustainability of groundwater and connected surface water systems. © Author(s) 2017. CC Attribution 3.0 License.
- ItemAustralian stable water isotopes – connecting the windows in time and space(Australasian Environmental Isotope Conference, 2022-11-14) Hughes, CENot available
- ItemThe benefits of a multidisciplinary team model for groundwater-surface water investigations, Thirlmere Lakes, NSW.(National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-25) Cowley, KL; Cohen, TJ; Forbes, MS; Barber, E; Allenby, J; Andersen, MS; Anibas, C; Glamore, W; Chen, SY; Johnson, F; Timms, W; David, K; McMillan, T; Cendón, DI; Peterson, MA; Hughes, CE; Krogh, MThe Thirlmere Lakes Research Program (TLRP) is a four-year collaborative multidisciplinary program designed to gain a whole-of-system understanding of the hydro-dynamics of a complex lake environment. The program was established from concerns that proximal aquifer interference activities were factors in recent lake level declines. Five research teams were established to investigate five adjacent lakes set within an entrenched meander bend located south-west of Sydney. The project involved lithological, geochemical and geochronological analysis from lake beds and surrounding slopes to understand lake evolution and determine potential past lake-drying events. Further geological understanding of the lake area was obtained from resistivity imaging (RI), ground penetrating radar (GPR), and analysis of rock cores that were drilled from two deep bores adjacent the lakes. Development of water balance budgets involved fine-scale on-site meteorological measurements including on-site evapotranspiration monitoring, combined with high-resolution bathymetry from RTK GPS, LiDAR surveying and drone photogrammetry. Groundwater-surface water interactions were measured using lake-bed multilevel temperature and pressure arrays, hydraulic head measurements and fine-scale isotope, major ion and environmental tracer time-series analysis. Preliminary findings indicate that the five lakes have been separated for over ~100,000 years and that the lakes themselves contain sediment that is possibly up to 250,000 years old. Assessing the modern dynamics we show that current lake level declines during a period of low rainfall are largely evaporation dominated. One lake however appears to have greater water storage in adjacent sediments providing compensatory inflows. In a second lake, there are indications of localised connectivity with shallow (≤18m) groundwater, but no evidence of connectivity with deeper aquifers. Geological surveys indicate a clay layer 6-8 m below the lakes and spatial variations in both sediment and rock geology. The influence of these geological features, including structures projecting towards the lakes, on groundwater storage and flow is the focus of ongoing research as is temporal variability and lake interactions at different lake levels. The benefits of the multidisciplinary team model include refining the research targeting areas of uncertainty and to enhance and calibrate each team’s results. This approach will provide a comprehensive whole-of-system model of the evolution and hydro-dynamics of a complex lake system. © The Authors
- ItemBiota dose assessment for environmental radiotracer releases in aquatic environments(Australian Nuclear Science and Technology Organisation, 2012-10-17) Hughes, CE; Johansen, MP; Wilson, RC; Copplestone, D; Vives i Batlle, JThe intentional release of short lived radioisotopes to trace transport and partitioning processes in the environment has been in decline in recent decades due to negative regulatory and public perceptions of the associated risks. Radiotracing is subject to significant regulatory requirements; in some jurisdictions one of these requirements is to demonstrate that radiation exposure to ecosystems is limited to ensure protection of populations of species. Radiation exposures from radiotracer studies are localised, transient and infrequent by nature, making it difficult to apply guidelines and biota dose assessment tools that are designed for chronic and widespread exposure scenarios. We will discuss the limitations of available guidelines and dose assessment methodologies when applied to radiotracer studies. A range of case studies for biota dose assessment will be presented using a variety of available tools including the ERICA Assessment Tool, the methodology of Copplestone et al. (2001) and a dynamic dose assessment model (Vives I Batlle et al., 2008). These case studies demonstrate that steady state, spatial homogeneity and bioavailability assumptions inherent in available dose assessment tools may lead to an over-estimate of dose to biota from radiotracer studies, and that many radiotracer studies can be conducted with minimal dose to biota.
- ItemBiotic, temporal and spatial variability of tritium concentrations in transpirate samples collected in the vicinity of a near-surface low-level nuclear waste disposal site and nearby research reactor(Elsevier Science Ltd, 2011-06-01) Twining, JR; Hughes, CE; Harrison, JJ; Hankin, SI; Crawford, J; Johansen, MP; Dyer, LLThe results of a 21 month sampling program measuring tritium in tree transpirate with respect to local sources are reported. The aim was to assess the potential of tree transpirate to indicate the presence of sub-surface seepage plumes. Transpirate gathered from trees near low-level nuclear waste disposal trenches contained activity concentrations of (3)H that were significantly higher (up to similar to 700 Bq L(-1)) than local background levels (0-10 Bq L(-1)). The effects of the waste source declined rapidly with distance to be at background levels within 10s of metres. A research reactor 1.6 km south of the site contributed significant (p < 0.01) local fallout (3)H but its influence did not reach as far as the disposal trenches. The elevated (3)H levels in transpirate were, however, substantially lower than groundwater concentrations measured across the site (ranging from 0 to 91% with a median of 2%). Temporal patterns of tree transpirate (3)H, together with local meteorological observations, indicate that soil water within the active root zones comprised a mixture of seepage and rainfall infiltration. The degree of mixing was variable given that the soil water activity concentrations were heterogeneous at a scale equivalent to the effective rooting volume of the trees. In addition, water taken up by roots was not well mixed within the trees. Based on correlation modelling, net rainfall less evaporation (a surrogate for infiltration) over a period of from 2 to 3 weeks prior to sampling seems to be the optimum predictor of transpirate (3)H variability for any sampled tree at this site. The results demonstrate successful use of (3)H in transpirate from trees to indicate the presence and general extent of sub-surface contamination at a low-level nuclear waste site. Crown Copyright © 2011, Elsevier Ltd.
- ItemThe canary or the coalmine? Isotopic evidence of drying climate versus groundwater outflow as the cause for recent losses from Thirlmere Lakes, NSW(National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-24) Peterson, MA; Cendón, DI; Hughes, CE; Crawford, J; Hankin, SI; Krogh, M; Cowley, KL; Cohen, TJ; Andersen, MS; Anibas, C; Glamore, W; Chen, SY; Timms, W; McMillan, TThe Thirlmere Lakes Research Program (TLRP) is a collaboration investigating water loss mechanisms in recent drying of five adjacent lakes, located 75 km south-west of Sydney. Some stakeholders and previous studies have perceived a correlation with local longwall coal mining history and suspect deep fracture outflow. Others suggest the lakes are simply responding to a drier climate, serving as the canary in the broader climate-change ‘coal mine’. ANSTO has applied recurrent isotopic and chemical monitoring of the lakes and adjacent groundwater over two years to unravel some of the mystery of their recent water losses. Each lake behaved uniquely, but they shared some common trends. Steady enrichment of stable water isotopes, 2H and 18O, indicates the dominance of evaporation, with minimal losses to groundwater or through transpiration. Lake Cl/Br ratios were very low and clustered in three groups, two trending away from initial ratios indicative of groundwater input. 3H and 14C show recent rainfall and/or runoff as the main contributors to lake waters, with apparent ages in the adjacent shallow groundwater up to several decades. High levels of 222Rn from shallow bores suggest a close association between the peats enclosing the lakes and 238 U from ancient erosion, or proximity of an underlying shale lens. The only deep piezometer (72-84 m) near the lakes showed negligible contributions from the lakes or recent surface water. The trends in isotopic and chemical parameters infer that evaporation is sufficient to explain recent water losses from most of these perched lakes. Trends in some lakes hint that these had previous inputs from groundwater. While the historical variability of groundwater input to the lakes remains unknown, there is no current evidence of major losses to groundwater. Thirlmere Lakes will exist only intermittently under dry climate conditions. © The Authors
- ItemChanges in below‐cloud evaporation affect precipitation isotopes during five decades of warming across China(American Geophysical Union, 2021-03-28) Wang, SJ; Jiao, R; Zhang, MJ; Crawford, J; Hughes, CE; Chen, FLBased on daily meteorological records for 651 sites across China during the period 1960–2018, we estimated the changes in isotopic variations in raindrops as they descend from cloud base to ground over past decades, and tested the sensitivity of isotopic variations to climate parameters like air temperature and relative humidity. Air temperature correlates positively and relative humidity correlates negatively with below‐cloud isotopic variation. Generally, the below‐cloud evaporation effect on precipitation isotopes in the arid and semi‐arid regions of China is much greater than that in the humid and semi‐humid regions, although the impact might be reduced under cold‐arid or hot‐humid conditions. With aridity increasing with distance from the coast, the continental effect of precipitation isotopes is modified due to the below‐cloud evaporation. The seasonal pattern of the measured isotopic composition in precipitation near the ground and estimated at cloud base, is still similar in most regions, although the seasonal range is higher at the ground. During the last five decades, the below‐cloud evaporation effect has enhanced for the cold and arid regions of China especially across Qinghai‐Tibet Plateau and Inner Mongolia, due to combined effects of increasing air temperature and decreasing relative humidity. Although the below‐cloud evaporation effect is not always the dominant factor influencing the variability of stable isotopes, it needs to be considered as one of the contributing factors. This enhanced effect may impact the interpretation of past climate based on stable water isotopes, particularly in paleoclimate studies using speleothems and tree rings. © 2021. American Geophysical Union
- ItemCharacterisation of the hydrology of an estuarine wetland(Elsevier, 1998-11) Hughes, CE; Binning, P; Willgoose, GRThe intertidal zone of estuarine wetlands is characterised by a transition from a saline marine environment to a freshwater environment with increasing distance from tidal streams. An experimental site has been established in an area of mangrove and salt marsh wetland in the Hunter River estuary, Australia, to characterise and provide data for a model of intertidal zone hydrology. The experimental site is designed to monitor water fluxes at a small scale (36 m). A weather station and groundwater monitoring wells have been installed and hydraulic head and tidal levels are monitored over a 10-week period along a short one-dimensional transect covering the transition between the tidal and freshwater systems. Soil properties have been determined in the laboratory and the field. A two-dimensional finite element model of the site was developed using SEEP/W to analyse saturated and unsaturated pore water movement. Modification of the water retention function to model crab hole macropores was found necessary to reproduce the observed aquifer response. Groundwater response to tidal fluctuations was observed to be almost uniform beyond the intertidal zone, due to the presence of highly permeable subsurface sediments below the less permeable surface sediments. Over the 36 m transect, tidal forcing was found to generate incoming fluxes in the order of 0.22 m3/day per metre width of creek bank during dry periods, partially balanced by evaporative fluxes of about 0.13 m3/day per metre width. During heavy rainfall periods, rainfall fluxes were about 0.61 m3/day per metre width, dominating the water balance. Evapotranspiration rates were greater for the salt marsh dominated intertidal zone than the non-tidal zone. Hypersalinity and salt encrustation observed show that evapotranspiration fluxes are very important during non-rainfall periods and are believed to significantly influence salt concentration both in the surface soil matrix and the underlying aquifer. © 1998 Elsevier Science B.V.
- ItemClimate change and groundwater(Springer, 2011-09-23) Hughes, CE; Cendón, DI; Johansen, MP; Meredith, KT