Browsing by Author "Hollins, SE"

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    A 35 ka record of groundwater recharge in south-west Australia using stable water isotopes
    (Elsevier B. V., 2020-05-15) Priestley, SC; Meredith, KT; Treble, PC; Cendón, DI; Griffiths, AD; Hollins, SE; Baker, AA; Pigois, JP
    The isotopic composition of groundwater can be a useful indicator of recharge conditions and may be used as an archive to infer past climate variability. Groundwater from two largely confined aquifers in south-west Australia, recharged at the northernmost extent of the westerly wind belt, can help constrain the palaeoclimate record in this region. We demonstrate that radiocarbon age measurements of dissolved inorganic carbon are appropriate for dating groundwater from the Leederville aquifer and Yarragadee aquifer within the Perth Basin. Variations in groundwater δ18O values with mean residence time were examined using regional and flow line data sets, which were compared. The trends in the regional groundwater data are consistent with the groundwater flow line data supporting the hypothesis that groundwater δ18O is a robust proxy for palaeo-recharge in the Perth Basin. A comparison between modern groundwater and rainfall water isotopes indicates that recharge is biased to months with high volume and/or intense rainfall from the westerly wind circulation and that this has been the case for the last 35 ka. Lower stable water isotope values are interpreted to represent recharge from higher volume and/or more intense rainfall from 35 ka through the Last Glacial Maximum period although potentially modulated by changes in recharge thresholds. The Southern Perth Basin groundwater isotopic record also indicates a trend towards higher volume and/or intense rainfall during the Mid- to Late Holocene. The long-term stable water isotope record provides an understanding of groundwater palaeo-recharge. Knowledge of recharge dynamics over long time scales can be used to improve current water sharing plans and future groundwater model predictions. © Crown Copyright 2019
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    A 35 ka record of groundwater recharge using stable water isotopes for Perth Basin in south-west Australia
    (National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-25) Priestley, SC; Meredith, KT; Treble, PC; Cendón, DI; Griffiths, AD; Hollins, SE; Baker, AA; Pigois, JP
    Objectives: As most large groundwater basins can contain ‘old’ groundwater where extraction exceeds groundwater recharge, knowledge of the past conditions and timing under which groundwater was recharged is needed to sustainably manage groundwater resources. Moreover, the isotopic composition of groundwater can be a useful indicator of rainfall isotope compositions and help to determine the drivers and impacts of rainfall and climate change. Applying isotopic tools to groundwater contained in regional aquifer systems can provide low-resolution information on recharge intensity, recharge source and past climatic conditions for the region. Design and Methodology: A dataset containing groundwater ages (14CDIC) and stable isotopes of water (δ18O and δ2H) from two regional groundwater systems within the Perth Basin, the Leederville Formation and Yarragadee Formation, were compiled to create a low-resolution palaeo-archive of groundwater recharge. Original data and results: The trends in stable isotopes of water over time in the regional groundwater data are consistent with groundwater flow line data supporting our hypothesis that groundwater stable isotopes are a proxy for palaeo-recharge. A comparison between modern groundwater and rainfall water isotopes indicates that recharge is biased to months with high volume and/or intense rainfall from the westerly wind circulation and that this has been the case for the last 35 ka. Lower stable water isotope values are interpreted to represent recharge from higher volume and/or more intense rainfall from 35 ka through the Last Glacial Maximum period although potentially modulated by changes in recharge thresholds. Conclusion: The groundwater isotope record is interpreted to be a low-resolution archive of recharge driven by changes in the relative intensity of past rainfall and recharge thresholds. This long-term stable isotopic recharge record provides a greater understanding of groundwater palaeo-recharge, and the connection between recharge and climate in the past. © The Authors
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    Application of neutron activatable tracers (NATs) for cohesive sediment transport studies in contaminated estuaries
    (International Atomic Energy Agency, 2004-10-29) Hollins, SE; Szymczak, R; Airey, PL; Peirson, WL; Payne, TE
    ANSTO and the University of NSW Water Research Laboratory (WRL) are investigating the migration of contaminants associated with cohesive sediments in Homebush Bay, Sydney. The study area is a highly urbanised and industrialised catchment with a long history of contamination [1]. Until 1890, when an ocean outfall was commissioned, domestic and industrial waste was discharged directly into Sydney Harbour [2]. Heavy metals and other hydrophobic pollutants have a distinct tendency towards solid phase partitioning. This means that the majority of heavy metals in the estuary are linked to particulates rather than occurring in the dissolved phase. Hence, in order to assess the impacts of the pollution and develop a scientific basis for remediation it is necessary to understand processes that resuspend and disperse the contaminated sediments. The study approach involved the evaluation of the numerical model of the processes using activatable tracer techniques [3]. An ideal tracer binds to the material of interest with high integrity and is detected with high sensitivity and selectivity. Tracers can be used to study sediment transport over extended periods and are therefore ideally suited to observing the impact of extreme weather events on sediment mobilisation by monitoring the distribution of the label before and after the event. The tracer must not only adhere to the cohesive sediment with high integrity but must be detectable with high efficiency, high sensitivity and relatively low cost. Identification of the optimum activatable tracer involved an assessment of the nuclear (Table I) and sorption properties. The implementation of the tracer study involved (a) labelling sediment from the study area with indium-115 in the laboratory and equilibrating for 3 weeks; (b) choosing a site where bathymetric surveys indicated significant recent accretion; (c) injection of the labelled sediment into an accurately located site in Homebush Bay (Fig. 1); (d) undertaking three surveys over the subsequent months; (e) analysis of samples via irradiation in the Fast Access Neutron facility in ANSTO’s research reactor, HIFAR and gamma counting on a High Purity Germanium detector3; and (f) data processing, where the tracer concentrations were contoured using the Surfer© routine and interpreted in terms of advective and dispersive transport using a Gaussian approximation (Fig. 2). Information on vertical transport was obtained by coring. These results are being used to evaluate a three-dimensional finite element model of the study area [4]. Estimates have been made of the aerial dispersion coefficients, of the surficial mixing due to bioturbation and of advective transport. This paper will focus on the optimum choice of the tracer for cohesive sediment transport studies and some early results.
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    Assessment of the aquifers in the West Canning Basin-Pardoo - application of isotopic and hydrogeochemical techniques
    (Australian Nuclear Science and Technology Organisation, 2014-01) Meredith, KT; Cendón, DI; Hankin, SI; Peterson, MA; Hollins, SE
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    Australian rainfall isotope variability and its relationship with groundwater
    (Copernicus Publications, 2017-07-10) Hughes, CE; Crawford, J; Cendón, DI; Meredith, KT; Hollins, SE
    Rainfall 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.
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    Carbon uptake in surface water food webs fed by paleogroundwater
    (American Geophysical Union, 2019-04-05) Mazumder, D; Saintilan, N; Hollins, SE; Meredith, KT; Jacobsen, GE; Kobayashi, T; Wen, L
    The use of 14C to elucidate sources of carbon within freshwater aquatic ecosystems is challenging the assumption that modern autochthonous carbon dominates energy flows. We measured the uptake of old carbon through several trophic levels of a wetland fed by groundwater of the Great Artesian Basin, Australia, the largest artesian basin in the world. Stable isotopes (δ13C and δ15N) and radiocarbon (14C) were used to quantify food chain links and connection between groundwater and surface water food webs. Our results suggest that old groundwater was the dominant carbon source even at the highest trophic levels, with predatory fish returning apparent carbon ages of up to 11 ka. Stable isotope analysis (δ13C and δ15N) identified trophic links between fish, aquatic insects, and algae with smaller contributions from particulate organic matter to the food webs. As natural mound springs and associated wetlands are the only source of reliable water during dry periods over vast areas of the western Great Artesian Basin, the result has potential implications for the interpretation of archaeological artefacts associated with indigenous passage within the interior. ©2019. ANSTO, Macquarie University, Commonwealth of Australia.
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    Characterization of the subsurface architecture and identification of potential groundwater paths in a clay-rich floodplain using multi-electrode resistivity imaging
    (Taylor & Francis Group, 2018-04-18) Guinea, A; Hollins, SE; Meredith, KT; Hankin, SI; Cendón, DI
    The interaction between surface water and groundwater in clay-rich fluvial environments can be complex and is generally poorly understood. Airborne electromagnetic surveys are often used for characterizing regional groundwater systems, but they are constrained by the resolution of the method. A resistivity imaging survey has been carried out in the Macquarie Marshes (New South Wales, Australia) in combination with water chemical sampling. The results have enabled the identification of buried palaeochannels and the location of potential recharge points. The data have been compared with previously published airborne electromagnetic data in the same area. Deeper less conductive features suggest that there is a potential connection between the Great Artesian Basin and groundwater contained within the shallow sand aquifer. Even though the chemistry of the groundwater samples does not indicate interaction with the Great Artesian Basin, the observed discontinuity in the saprolite implies potential for this to happen in other locations. The interaction between surface water and groundwater in clay-rich fluvial environments can be complex and is generally poorly understood. Airborne electromagnetic surveys are often used for characterizing regional groundwater systems, but they are constrained by the resolution of the method. A resistivity imaging survey has been carried out in the Macquarie Marshes (New South Wales, Australia) in combination with water chemical sampling. The results have enabled the identification of buried palaeochannels and the location of potential recharge points. The data have been compared with previously published airborne electromagnetic data in the same area. Deeper less conductive features suggest that there is a potential connection between the Great Artesian Basin and groundwater contained within the shallow sand aquifer. Even though the chemistry of the groundwater samples does not indicate interaction with the Great Artesian Basin, the observed discontinuity in the saprolite implies potential for this to happen in other locations. © 2018 International Association of Hydrological Sciences (IAHS)
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    A combined multidisciplinary kinetic modeling approach for determination of coastal ecosystem contaminant fluxes
    (Goldschmidt, 2006-08-26) Szymczak, R; Twining, JR; Hollins, SE; Mazumder, D; Creighton, NM
    The historical operation of manufacturing, chemical and other industries in the Sydney Harbour catchment over many decades has left a legacy of high chemical contamination in the surrounding catchment. These contaminants are now seriously impacting on incident commercial fisheries and public utilisation of estuarine resources. Elucidation of environmental processes is the key to effective ecosystem management, however few tools are available to predict their inter-relationships, rates and directions. This work seeks to combine GIS, contaminant transport, ecological, and bioaccumulation models to improve the accuracy and specificity of a probabilistic ecological risk assessment strategy. This study has four components: (1) determination of chemical linkages between high trophic order species and different habitats resources using stable isotopic analyses of carbon and nitrogen. These studies identify trophic cascades forming the basis for selection of biota for contaminant transfer experiments; (2) short-term (weeks – months) chronology and geochemistry of sediment cores and traps in Homebush Bay to determine rates of sedimentation and resuspension (using environmental/cosmogenic 7-Be). Models derived from these studies provide the contaminants levels against which risk is assessed; (3) biokinetic studies using proxy radiotracer isotopes (eg. 75-Se & 109-Cd for analogous stable metals) of the uptake and trophic transfer of contaminants by specific estaurine biota. Here we identify the rates and extent to which contaminants accumulated and transferred to predators/seafoods; and (4) application of a probabilistic ecological risk assessment model (AQUARISK) set to criteria determined by stakeholder consensus. Here we report initial results of the distribution of natural isotopes and redistribution of artificial isotopes injected into ecological compartments to determine the key trophic linkages, contaminant pathways and their rates in temperate estuarine systems of Sydney Harbour & Botany Bay (Australia).
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    A comparison between direct and pan-derived measurements of the isotopic composition of atmospheric waters
    (The Modelling and Simulation Society of Australia and New Zealand Inc., 2011-12-12) Azcurra, CS; Hughes, CE; Parkes, SD; Hollins, SE; Gibson, JJ; McCabe, MF; Evans, JP
    The stable isotopes of water can be used to examine and quantify the contribution to atmospheric moisture from evaporation, transpiration and surface-waters. However, obtaining extensive and ongoing time series data of the isotopic composition of atmospheric moisture has been difficult. Presented here is an alternate method using an isotope mass balance approach to estimate the isotopic composition of atmospheric moisture using water samples collected from class A evaporation pans. While this evaporation pan method does not provide the high-resolution time series data that can be obtained from an isotope analyser taking in-situ measurements of atmospheric moisture, the method is relatively simple and inexpensive to set-up and maintain. In this preliminary investigation, a comparison between the isotopic composition of atmospheric moisture estimated from the evaporation pan method and in-situ measurements of the isotopic composition of water vapour using a Fourier Transform Infrared (FTIR) spectrometer deployed at the Lucas Heights weather station in New South Wales is undertaken. Through comparison of the two series of hydrogen isotope data, an assessment of the evaporation pan method can be made. Although there was some agreement between the isotopic composition of vapour measured by the FTIR spectrometer and the estimation for the atmospheric moisture (R2 = 0.49), the comparison is sensitive to climatic parameters that vary significantly within a 24-hour period such as the relative humidity of air and the air and pan temperatures. Inverting the model to use the FTIR spectrometer measurements at an hourly resolution improved the performance of the model (R2 =0.57). However, this also revealed that the model produced more depleted values of the evaporation pan water isotopes than those observed. In contrast, there was a variable relationship between the modelled and observed isotope values of atmospheric moisture. These conflicting results will need to be resolved before the evaporation pan method is broadly applied in isotope hydrology. © 2011 The Modelling and Simulation Society of Australia and New Zealand Inc.
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    Constraining hydrochemical pathways in a small internally draining basin (Lake George Basin, NSW) using isotopes of the water molecule
    (Geological Society of Australia, 2014-07-07) Short, MA; McPhain, DC; Hollins, SE
    Lake George, located in the Southern Tablelands of New South Wales, is a shallow, intermittent lake with highly variable salinity and water levels. The lake is the focus of drainage for a small internally draining basin containing six sub-catchments. It is currently believed that the lake’s water level is primarily affected by the short- and long-term variations in precipitation, runoff and evaporation. Contributions from the regional groundwater are thought to be low because of the thick (~40 m) clay unit that underlies the modern extent of the lake. As a result, the lake’s hydrograph, which is one of the oldest in the world, has recorded droughts and wet periods of southeastern Australia over the last 200 years. In this project, water chemistry and physical hydrometeorological data are being collected to determine hydrochemical pathways and recharge rates. This will provide much needed information regarding the sustainability of the Bungendore town water supply as well as identify potential risks to water quality in the basin. This project also forms one part of a much larger project to investigate the landscape and human evolution of the Lake George Basin. Four precipitation samplers have been installed at three sites around the catchment – one to the north of the lake at Winderadeen homestead, one to the south of the lake at Bungendore’s post office, and two at a rocky outcrop (‘Rocky Point’) on the eastern shore of Lake George. Three precipitation samplers (one located at each site) are used to collect monthly composite precipitation samples for deuterium and oxygen-18 analysis, and elemental concentrations. The additional sampler located at Rocky Point is used to collect precipitation for tritium analysis. In months when precipitation is too low to collect sufficient sample volume (~1 L), monthly samples are combined. These data are being combined with deuterium, oxygen-18, tritium and elemental compositions, as well as hydrometeorological measurements, of surface water, groundwater and atmospheric moisture from around the basin to help constrain recharge areas and rates, primary hydrochemical pathways and controls on water quality. Deuterium and oxygen-18 compositions indicate that groundwater is primarily recharged by winter rainfall. Despite variable precipitation compositions throughout the year, creek water maintains a winter rainfall/groundwater isotopic year-round, which may indicate that the creeks of the basin are fed by aquifers and through-flow rather than fresh precipitation. This is also supported by low tritium activity. A local evaporation line has also been determined for Lake George during the period July 2013 (after high rainfall) to November (when the lake dried out due high evaporation rates.
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    Daily observations of rainfall, vapour and pan water δ2H for improved quantification of atmospheric and terrestrial water interactions
    (American Geophysical Union, 2012-12-03) Hughes, CE; Azcurra, CS; Parkes, SD; Hollins, SE; McCabe, MF; Evans, JP; Pickering, D; Gibson, JJ; Edwards, K
    The stable isotopes of water (δ2H, δ18O) have been used extensively to track the movement of water through the hydrological cycle. As water moves through the hydrological cycle, its isotopic composition changes (fractionation) as a result of phase changes and interactions with other waters. When combined with other measurements of water fluxes and volumes, the stable isotopes can provide information about sources, processing, and transport of water suitable for determining water and energy balances. While the isotopic composition of atmospheric moisture influences the isotopic composition of terrestrial waters, obtaining ongoing time series data of this has been difficult. One method for estimating the isotopic composition of atmospheric moisture combines the Craig-Gordon isotopic evaporation model with a mass balance approach, using water samples collected from Class A evaporation pans at weekly intervals. The method assumes steady-state conditions and thus does not represent the highly variable meteorological conditions that can strongly influence fractionation. Although water-sampling regimes cannot match the frequency of the observed variability in meteorological conditions, increasing the sampling resolution to a sub-weekly resolution will more closely align isotopic measurements with meteorological conditions and allow the assessment of established water isotope relationships at a greater temporal frequency. An alternate method for estimating the isotopic composition of atmospheric moisture is based on local precipitation being in equilibrium with atmospheric moisture. As per the evaporation pan method, it is assumed that steady-state conditions apply. At the Lucas Heights weather station in south-eastern Australia, atmospheric moisture water isotopes (δA) have been directly measured at sub-hourly intervals using a Fourier Transform Infrared (FTIR) spectrometer. This hydrogen isotope time series was evaluated against daily observations of isotopes in water from a Class A evaporation pan (δL) and in precipitation (δP) collected from the same site. This study assesses the validity of established (steady-state) relationships between liquid and vapor water isotopes for interactions that have been measured at the medium-resolution temporal scale, and provides a basis for improving flux estimates based on an isotope mass balance approach. ©Author(s) 2012
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    Defining the stable isotope composition of rainfall for groundwater studies in Australia
    (International Association of Hydrogeologists, 2013-09-19) Hughes, CE; Hollins, SE; Crawford, J; Meredith, KT; Parkes, SD
    The stable isotopes of water, d2H and d18O, are conservative tracers available for studying mixing of water in the hydrosphere. But they are not completely conservative as they undergo fractionation as a result of hydrological processes such as evaporation, precipitation, ice and snow formation and melting, and geothermal activity. The fractionation can be used to understand the provenance and history of groundwater and to define end members for mixing studies. Measurements of stable water isotopes in Australian rainfall have been made monthly at six coastal sites and Alice Springs since 1962 as part of the Global Network of isotopes in Precipitation (GNIP). Since 2006 this network has been expanded to include seven inland sites in New South Wales, Queensland, South Australia and Western Australia. in addition, event-based studies have been conducted at four locations in the Sydney region since 2005. These data have been analysed to determine local meteoric water lines, weighted averages and to investigate the relationships between rainfall isotopic composition, temperature and precipitation amount. For one Sydney region location, Mt Werong, the effect of moisture source, rainout and the prevailing synoptic conditions were investigated on an event basis over four years from 2005 and 2009. We will present results from these studies as well as a precipitation weighted method for determining a meteoric water line that is particularly applicable to areas with hot dry summers and wet winters such as SW Western Australia.
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    Deuterium and oxygen-18 ratios in rainfall and streamflow in a major drinking water catchment near Sydney, Australia, during drought
    (International Atomic Energy Agency, 2007-05-21) Hughes, CE; Fischer, MJ; Stone, DJM; Hollins, SE
    The Warragamba catchment near Sydney, Australia, is in the midst of a major drought that is threatening water supplies for Australia's largest city. Over a period of 18 months 227 event based rainfall samples were collected at four locations, 74 streamflow samples were collected from the four major inflowing rivers and their tributaries and and 45 reservoir samples were collected at various depths from Warragamba dam. The samples were analysed for δD and δ18O. These data provide a baseline dataset for establishment of a local meteoric water line for the Sydney region and for use in modelling of flow pathways and weather patterns in the Warragamba catchment.
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    Deuterium and oxygen-18 ratios in rainfall and streamflow in a major drinking water catchment near Sydney, Australia, during drought
    (International Atomic Energy Agency, 2007) Hughes, CE; Fischer, MJ; Stone, DJM; Hollins, SE
    The Warragamba catchment near Sydney, Australia, is in the midst of a major drought that is threatening water supplies for Australia's largest city. Over a period of 18 months 227 event based rainfall samples were collected at four locations, 74 streamflow samples were collected from the four major inflowing rivers and their tributaries and and 45 reservoir samples were collected at various depths from Warragamba dam. The samples were analysed for δD and δ18O. These data provide a baseline dataset for establishment of a local meteoric water line for the Sydney region and for use in modelling of flow pathways and weather patterns in the Warragamba catchment.
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    Drought
    (Springer, 2013-01-01) Hollins, SE; Dodson, JR
    Drought is a severe natural hazard that affects more people than any other natural disaster. It is usually only recognized as a natural hazard when social, economic, or environmental impacts become apparent. Drought is different from many other natural hazards in that it lacks easily identified onsets and terminations (Maybank et al., 1995). It is also unusual in that it is a hazard of scarcity rather than one of excess. Drought is a natural, recurring pattern of climate that occurs within nearly all climatic regions. However, it is not just a physical phenomenon or natural event caused by changes in climatic conditions. Rather, drought results from a connection between the natural event of lower than expected precipitation, and the demand of human usage on water supplies (Wilhite, 2000). Anthropogenic activities can exacerbate the severity and impacts of drought, but within a natural variability range. © 2013, Springer.
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    Effect of acidification on elemental and isotopic compositions of sediment organic matter and macro-invertebrate muscle tissues in food web research
    (Wiley-Blackwell, 2010-10-30) Mazumder, D; Iles, J; Kelleway, JJ; Kobayashi, T; Knowles, L; Saintilan, N; Hollins, SE
    Stable isotope techniques in food web studies often focus on organic carbon in food sources which are subsequently assimilated in the tissue of consumer organisms through diet. The presence of non-dietary carbonates in bulk samples can affect their δ13C values, altering how their results are interpreted. Acidification of samples is a common practice to eliminate any inorganic carbon present prior to analysis. We examined the effects of pre-analysis acidification on two size fractions of sediment organic matter (SOM) from marine and freshwater wetlands and pure muscle tissue of a common freshwater invertebrate (Cherax destructor). The elemental content and isotopic ratios of carbon and nitrogen were compared between paired samples of acidified and control treatments. Our results showed that acidification does not affect the elemental or isotopic values of freshwater SOM. In the marine environment acidification depleted the δ13C and δ15N values of the fine fraction of saltmarsh and δ15N values of mangrove fine SOM. Whilst acidification did not change the elemental content of invertebrate muscle tissue, the δ13C and δ15N values were affected. We recommend to researchers considering using acidification techniques on material prepared for stable isotope analysis that a formal assessment of the effect of acidification on their particular sample type should be undertaken. Further detailed investigation to understand the impact of acidification on elemental and isotopic values of organic matter and muscular tissues is required. © 2010, Wiley-Blackwell. The definitive version is available at www3.interscience.wiley.com
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    The effect of saline groundwater exchange, evaporation and variable river flows and on stable isotopes (18O and 2H) and major ion concentrations along the Darling River, NSW, Australia
    (European Geosciences Union, 2009-04-22) Meredith, KT; Hughes, CE; Hollins, SE; Cendón, DI; Hankin, SI
    Australia's longest river, the Darling River, faces extreme pressure from drought and over extraction of water from its catchment. The lack of detailed baseline hydrochemical and isotopic data for the Darling River has prompted research aimed at using hydrological tracers to assess water gains and losses within the Darling River Drainage Basin. This study uses temporal hydrochemical and stable isotope data (18O and 2H) that has been monitored from gauging stations along the Barwon-Darling catchment over a five-year period from 2002 to 2007 as part of the Global Network for Isotopes in Rivers (GNIR) monitoring programme. Stream flow data, monthly δ18O and δ2H values and major ion chemistry is presented. Individual flow events were found to be isotopically distinct but the LELs that develop after these events have a very similar slope indicating similar climatic conditions across this region. During low flow conditions, salt concentrations increase systematically, δ18O and δ2H become enriched and d-excess becomes more negative indicating significant evaporation. Flow events input isotopically depleted fresh waters to the system and the d-excess returns towards the local meteoric water line. The major ions increase in concentration at a greater rate at Louth than they do at upstream at Bourke or downstream at Wilcannia, despite similar decreases in flow rates for all three sites. The hydrological response of the river to drought has had detrimental affects on the surface water system because it provides a pathway for saline groundwater to discharge into the river system. © Author(s) 2009
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    Evaporation and concentration gradients created by episodic river recharge in a semi-arid zone aquifer: Insights from Cl−, δ18O, δ2H, and 3H
    (Elsevier B. V., 2015-10) Meredith, KT; Hollins, SE; Hughes, CE; Cendón, DI; Chisari, R; Griffiths, AD; Crawford, J
    This study has significantly advanced our understanding of the origin of groundwater recharge in a semi-arid zone region of the Darling River catchment, Australia. The generally accepted hypothesis in arid zone environments in Australia that river water forms the primary groundwater recharge source has proven difficult to monitor. This is due to the time lags between large floods, the remoteness and expense of studying these hydrologically complex systems in detail. In addition, the highly episodic nature of dryland rivers complicates the interpretation of the groundwater signal. A range of hydrochemical tracers (chloride, oxygen-18, deuterium and tritium) measured in rain, river water, soil water and groundwater were used in this multi-year study to trace the pathways of groundwater recharge under wet and dry climatic conditions. The evaporation and Cl concentrations observed in the unsaturated zone confirmed that small volumetric inputs from periodic rainfall were not the major recharge mechanism. Sampling which included an overbank flooding event in March 2012 provided firm evidence for groundwater originating from high flow episodic river recharge. The use of long-term environmental data to understand how economically important water resources respond to climate change with increasing temperatures is considered essential for future sustainability. Crown Copyright ©2015 Published by Elsevier B.V.
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    Evaporative isotope enrichment as a constraint on reach water balance along a dryland river
    (Taylor & Francis, 2008-03) Gibson, JJ; Sadek, MA; Stone, DJM; Hughes, CE; Hankin, SI; Cendón, DI; Hollins, SE
    Deuterium and oxygen-18 enrichment in river water during its transit across dryland region is found to occur systematically along evaporation lines with slopes of close to 4 in H-2-O-18 space, largely consistent with trends predicted by the Craig-Gordon model for an open-water dominated evaporating system. This, in combination with reach balance assessments and derived runoff ratios, strongly suggests that the enrichment signal and its variability in the Barwon-Darling river, Southeastern Australia is acquired during the process of evaporation from the river channel itself, as enhanced by the presence of abundant weirs, dams and other storages, rather than reflecting inherited enrichment signals from soil water evaporation in the watershed. Using a steady-state isotope mass balance analysis based on monthly O-18 and H-2, we use the isotopic evolution of river water to re-construct a perspective of net exchange between the river and its contributing area along eight reaches of the river during a drought period from July 2002 to December 2003, including the duration of a minor flow event. The resulting scenario, which uses a combination of climatological averages and available real-time meteorological data, should be viewed as a preliminary test of the application rather than as a definitive inventory of reach water balance. As expected for a flood-driven dryland system, considerable temporal variability in exchange is predicted. While requiring additional real-time isotopic data for operational use, the method demonstrates potential as a non-invasive tool for detecting and quantifying water diversions, one that can be easily incorporated within existing water quality monitoring activities. © 2008, Taylor & Francis Ltd.
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    Evaporative losses from the Darling River, NSW, during drought from 2002-2005
    (Australasian Environmental Isotope Conference, 2009-12-03) Hughes, CE; Meredith, KT; Cendón, DI; Hollins, SE
    The Darling-Barwon River system faces extreme pressure from drought and over extraction of water from its catchment. Isotopic tracers can be used to assess water gains and losses and to distinguish evaporative losses from groundwater recharge or pumping. Stable water isotope (δ2H and δ18O) and major ion data was collected monthly at nine stations from Mungindi, near the Queensland border, to Burtundy, above the confluence with the Murray River, between 2002 and 2005, as part of the Global Network for Isotopes in Rivers (GNIR) monitoring programme [1]. This data has been used to investigate groundwater exchange, evaporative and pumping losses along the Barwon/Darling River [2,3] during an extended dry period with relatively minor flow events. Individual flow events were found to be isotopically distinct but the local evaporation lines (LEL, Fig 1(a)) that develop after these events have a very similar slope indicating similar climatic conditions across this region. During low flow conditions, salt concentrations increase systematically, δ2H and δ18O become enriched and deuterium excess becomes more negative indicating significant evaporation. Flow events input isotopically depleted fresh waters to the system and as a result the deuterium excess returns towards the local meteoric water line. Fig. 1(b) shows this progressive enrichment and rapid depletion following flow events for Wilcannia during this study period. These stable water isotope data can be used to calculate the amount of river or lake water lost to evaporation, and an approximate scale of evaporative losses for the Barwon/Darling River system from 2002 to 2005 is shown in Fig. 1(a). During extended dry periods evaporative enrichment of δ2H and δ18O indicates increasing evaporative losses as water moves downstream with up to 80% evaporative losses for water in the lower reaches of the Darling River and in the Menindee lakes system. In other reaches of the river there is evidence that the hydrological response of the river to drought has increased saline groundwater discharge into the river system resulting in detrimental affects on water quality [2]. Discrepancies between isotope based mass balances, which can improve the quantification of evaporation losses and groundwater inputs, and standard flow gauging based models can be used to detect ungauged losses and gains [3]. These may include irrigation or domestic water use, bank storage or groundwater recharge. These are examples of how isotope tracers can help to quantify the hidden hydrological fluxes that impact on flow particularly during drought.