ANSTO :: Browsing by Author "Meredith, KT"

Browsing by Author "Meredith, KT"

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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
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
Application of stable noble gases, 85Kr and 39Ar to investigate the freshwater lens on Rottnest Island, Western Australia
(Goldschmidt, 2017-08-13) Kersting, A; Aeschbach, W; Deslandes, A; Meredith, KT; Peterson, MA; Purtschert, R; Suckow, A
We report on a multi-tracer study of a freshwater lens on Rottnest Island west of Perth (Western Australia). The potable water supply of this carbonate island is entirely based on a shallow freshwater lens ‘floating’ on more saline water. Former studies (Bryan 2016) identified rain as the sole source of the fresh groundwater and that this very vulnerable system is threatened by anthropogenic usage and reduced rainfall due to climate change, causing salt water intrusion.Since the freshwater lens only has a thickness of approx. 20m, even the short screens of the observation wells (1-2m length) cause significant mixing of water of different ages. The combination of tritium (3H) and radiocarbon (14C) used earlier cannot resolve details of the age distribution because of the low values for tritium in precipitation on the southern hemisphere and because of mixing corrosion of the carbonate aquifer together with seawater intrusion changing the initial radiocarbon values. Therefore,this study focussed on the applicationof 85Kr(half-life 10,8yr) and 39Ar (half-life 269yr) as well as the stable noble gases. Here 85Kr complements 3H to resolve the component of very young waterin the age distribution,whereas39Ar fillsthe dating gap between 3H and 14C. The heavy noblegases (Ar, Kr, Xe) can give additional information on the infiltration of freshwater or seawater and 4He can identify admixtures of old water.
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
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.
Carbon cycling in sub-Antarctic and Antarctic lakes
(American Geophysical Union (AGU), 2021-12-17) McDonough, LK; Meredith, KT; Saunders, KM; Baker, AA
Between 2000 and 2010, anthropogenic carbon emissions rose at rates of 2.2% year-1, a 70% increase above the annual rates observed between 1970 and 2000. This has accelerated global temperature increases. As a result, carbon fluxes to and from aquatic environments have changed, affecting microbial community compositions, and impacting the ability of some environments to act as carbon stores. Whilst the factors influencing nutrient cycling in many aquatic environments, including major rivers and oceans, have been well studied, little is known about the biogeochemical processes driving aquatic carbon cycling in sub-Antarctic and Antarctic lakes, and how this may be impacted by climate change. This is in part because sampling programs designed for such isolated environments take years to plan and require international collaboration. The isolation of these lakes however mean that many are relatively undisturbed by human activities, making them ideal locations to study the interactions between hydrological and biogeochemical processes, and the impact of climate change on natural carbon sources, transformation and storage. We aim to analyse Antarctic and sub-Antarctic lake water using organic carbon characterisation techniques such as fluorescence, liquid chromatography organic carbon detection and synchrotron characterisation, as well as radiocarbon and stable carbon isotopes of dissolved organic carbon (14CDOC and 13CDOC) and dissolved inorganic carbon (14CDIC and 13CDIC). This will allow us to identify key carbon sources such as terrestrial vegetation, groundwater and permafrost thaw, carbon age, and cycling via biodegradation or other processing mechanisms. The data collected for this project will form the first comprehensive spatial and temporal survey of dissolved carbon in both organic and inorganic phases in lakes across the region, aimed at understanding present-day environmental processes and their drivers. These data also have the potential to calibrate palaeo-records such as peat and lake archives which will assist in the understanding of the impacts of large-scale climate variability and environmental changes that may occur in the future.
Carbon dynamics in a Late Quaternary-age coastal limestone aquifer system undergoing saltwater intrusion
(Elsevier, 2017-12-31) Bryan, E; Meredith, KT; Baker, AA; Andersen, MS; Post, VEA
This study investigates the inorganic and organic aspects of the carbon cycle in groundwaters throughout the freshwater lens and transition zone of a carbonate island aquifer and identifies the transformation of carbon throughout the system. We determined 14C and 13C carbon isotope values for both DIC and DOC in groundwaters, and investigated the composition of DOC throughout the aquifer. In combination with hydrochemical and 3H measurements, the chemical evolution of groundwaters was then traced from the unsaturated zone to the deeper saline zone. The data revealed three distinct water types: Fresh (F), Transition zone 1 (T1) and Transition zone 2 (T2) groundwaters. The 3H values in F and T1 samples indicate that these groundwaters are mostly modern. 14CDOC values are higher than 14CDIC values and are well correlated with 3H values. F and T1 groundwater geochemistry is dominated by carbonate mineral recrystallisation reactions that add dead carbon to the groundwater. T2 groundwaters are deeper, saline and characterised by an absence of 3H, lower 14CDOC values and a different DOC composition, namely a higher proportion of Humic Substances relative to total DOC. The T2 groundwaters are suggested to result from either the slow circulation of water within the seawater wedge, or from old remnant seawater caused by past sea level highstands. While further investigations are required to identify the origin of the T2 groundwaters, this study has identified their occurrence and shown that they did not evolve along the same pathway as fresh groundwaters. This study has also shown that a combined approach using 14C and 13C carbon isotope values for both DIC and DOC and the composition of DOC, as well as hydrochemical and 3H measurements, can provide invaluable information regarding the transformation of carbon in a groundwater system and the evolution of fresh groundwater recharge. © 2017 Elsevier B.V
Carbon source and sink investigations in a Late Quaternary-age coastal limestone aquifer using radiocarbon of dissolved inorganic and organic carbon
(National Centre for Groundwater Research And Training, 2017-07-11) Bryan, E; Meredith, KT; Baker, AA; Andersen, MS; Post, VEA
This study aims to investigate the inorganic and organic aspects of the carbon cycle in groundwaters throughout a freshwater lens and mixing zone of a carbonate island aquifer and identify the sources of carbon that dissolve in the groundwater. Groundwater samples were collected from shallow (5-20 m) groundwater wells on a carbonate island in Western Australia and analysed for inorganic ions, stable water isotopes (δ18O, δ2H), 3H, 14C and 13C carbon isotope values of DIC and DOC. The composition of groundwater DOC was investigated by Liquid Chromatography-Organic Carbon Detection (LC-OCD) analysis. The presence of 3H (0.12 to 1.35 TU) in most samples indicates that groundwaters on the island are modern, however the measured 14CDIC values (8.4 to 97.2 pmc) would suggest that the carbon in most samples is older due to carbonate dissolution and recrystallisation reactions. 14CDOC values (46.6 to 105.6 pMC) were higher than 14CDIC values and were well correlated with 3H values. Deeper, saline groundwaters were characterised by an absence of 3H, and lower 14CDOC values. The DOC composition of these groundwaters was found to be different to fresher groundwaters, with higher proportions of humic substances. The 3H free, saline waters are hypothesised to be old, remnant sea water resulting from a sea level highstand that occurred between ~4.5 and 4.3 ka ago. This study shows that a combined approach utilising both DIC and DOC tracers, as well as 3H, is required to identify the sources and evolution of carbon in groundwater, and the processes that effect the application of 14C dating to groundwaters. This is important for understanding the evolution of groundwater resources and is essential for residence time calculations.
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.
Carbon-14 in unsaturated zone gases: implications for groundwater dating
(International Association of Hydrogeologists, 2013-09-19) Wood, C; Cook, PG; Harrington, GA; Meredith, KT; Kipfer, K
Quantitative interpretation of the carbon-14 activity (14C) of dissolved inorganic carbon (DIG) in groundwater requires an understanding of the various chemical and physical processes that can vary the initial 14C activity from that of the original atmospheric carbon dioxide (CO2) source. Such processes include radioactive decay, carbonate mineral dissolution, isotope exchange, decay of organic matter and molecular diffusion. Many geochemical correction models exist to account for some of these processes (e.g., Fontes and Garnier, 1979). However in most existing correction schemes, it is assumed that the 14C activity of CO2 in the unsaturated zone is in equilibrium with the atmosphere (i.e., 14C:12C is the same as the atmospheric ratio). This assumption is rarely tested and in several cases has been found to be false (eg. Bacon and Keller, 1998). Not accounting for the influence of unsaturated zone processes on "C may lead to an over-estimate of groundwater residence time, or an under-estimate of fluxes derived from measured 14C data in groundwater. In this study we examine carbon isotope processes in deep unsaturated zone proles (up to 30m in depth) in arid central Australia. At multiple sites, multi-levelled proles were sampled for both unsaturated zone gas and groundwater for “C analysis. Chlorofluorcarbon (CFC-11 and CFC-12) samples were also collected in unsaturated zone gas. At all sites we observe a decrease in the 14C activity of unsaturated zone gas with depth, from approximately 110 pmC near ground surface to 50-80 pmC immediately above the water table. The measured 14C data was reproduced in a model using Hydrus, with CFC-12 concentrations used to constrain the gas transport parameters. Modelling showed that the decrease in 14C can be explained by CO2 production from different sources at different depths in the unsaturated zone (eg. plant root respiration at shallower depths, oxidation of dead organic matter at greater depths). This work has important implications for using raw 14C results for groundwater dating projects but also improves our understanding of carbon processes within the unsaturated zone. The results of this work are particularly important in arid environments where groundwater residence time is typically long (>1,000 years old) and unsaturated zones may be deep (>1 m).
Caves demonstrate decrease in rainfall recharge of southwest Australian groundwater is unprecedented for the last 800 years
(Springer Nature, 2023-06-09) Priestley, SC; Treble, PC; Griffiths, AD; Baker, AA; Abram, NJ; Meredith, KT
Billions of people worldwide rely on groundwater. As rainfall in many regions in the future is projected to decrease, it is critical to understand the impacts of climate change on groundwater recharge. The groundwater recharge response to a sustained decrease in rainfall across southwest Australia that began in the late 1960s was examined in seven modern speleothems and drip waters from four caves. These show a pronounced increase or uptick in regional drip water and speleothem oxygen isotopic composition (δ18O) that is not driven by a change in rainfall δ18O values, but is in response to the shallow karst aquifers becoming disconnected from rainfall recharge due to regional drying. Our findings imply that rainfall recharge to groundwater may no longer be reliably occurring in this region, which is highly dependent on groundwater resources. Examination of the longer speleothem record shows that this situation is unprecedented over the last 800 years. © The Authors - Open Access licensed under a Creative Commons Attribution 4.0 International Licence.
Caves provide early warning of unprecedented decrease in rainfall recharge of groundwater
(Research Square, 2022-05-02) Priestley, SC; Treble, PC; Griffiths, AD; Baker, AA; Abram, NJ; Meredith, KT
Billions of people worldwide rely on groundwater. As rainfall in many regions in the future is projected to decrease, it is critical to understand the impacts of climate change on groundwater recharge. In this study, five caves record a consistent response to a sustained decrease in rainfall across southwest Australia that began in the late 1960s, characterised by a pronounced increase or ’uptick’ in dripwater and speleothem oxygen isotopic composition (δ18O). It is demonstrated that the uptick is in response to the shallow karst aquifers becoming disconnected from recharge due to regional drying. Our findings imply that rainfall recharge to groundwater across this region is no longer reliably occurring. Examination of the longer speleothem record shows that this is unprecedented over at least the last 800 years. A global network of cave dripwater monitoring would serve as an early warning of reduced groundwater recharge elsewhere, while evidence for upticks in speleothem paleoclimate records would provide a longer-term context to evaluate if current groundwater recharge changes are outside the range of natural variability. This study also validates speleothems as recorders of past hydroclimate via amplification of the δ18O signal by karst hydrology highlighting that speleothem δ18O are records of recharge, rather than a direct proxy for rainfall. © 2022 The Authors
Changes in global groundwater organic carbon driven by climate change and urbanization
(Springer Nature, 2020-03-09) McDonough, LK; Santos, IR; Andersen, MS; O'Carroll, DM; Rutlidge, H; Meredith, KT; Oudone, PP; Bridgeman, J; Gooddy, DC; Sorensen, JPR; Lapworth, DJ; MacDonald, AM; Ward, J; Baker, AA
Climate change and urbanization can increase pressures on groundwater resources, but little is known about how groundwater quality will change. Here, we use a global synthesis (n = 9,404) to reveal the drivers of dissolved organic carbon (DOC), which is an important component of water chemistry and substrate for microorganisms that control biogeochemical reactions. Dissolved inorganic chemistry, local climate and land use explained ~ 31% of observed variability in groundwater DOC, whilst aquifer age explained an additional 16%. We identify a 19% increase in DOC associated with urban land cover. We predict major groundwater DOC increases following changes in precipitation and temperature in key areas relying on groundwater. Climate change and conversion of natural or agricultural areas to urban areas will decrease groundwater quality and increase water treatment costs, compounding existing constraints on groundwater resources. © 2020, The Author(s)
Changes in groundwater dissolved organic matter character in a coastal sand aquifer due to rainfall recharge
(Elsevier, 2020-02-01) McDonough, LK; O'Carroll, DM; Meredith, KT; Andersen, MS; Brügger, C; Huang, HX; Rutlidge, H; Behnke, MI; Spencer, RGM; McKenna, AM; Marjo, CE; Oudone, PP; Baker, AA
Dissolved organic matter (DOM) in groundwater is fundamentally important with respect to biogeochemical reactions, global carbon cycling, heavy metal transport, water treatability and potability. One source of DOM to groundwater is from the transport of organic matter from the vadose zone by rainfall recharge. Changes in precipitation patterns associated with natural climate variability and climate change are expected to alter the load and character of organic matter released from these areas, which ultimately impacts on groundwater quality and DOM treatability. In order to investigate potential changes in groundwater DOM character after rainfall recharge, we sampled shallow groundwater from a coastal peat-rich sand aquifer in New South Wales, Australia, during an extended period of low precipitation (average daily precipitation rate < 1.6 mm day−1 over the 8 months prior to sampling), and after two heavy precipitation events (84 mm day−1 and 98 mm day−1 respectively). We assess changes in DOM composition after correcting for dilution by a novel combination of two advanced analytical techniques: liquid chromatography organic carbon detection (LC-OCD) and negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). We also assess changes in water chemistry pre- and post-rainfall. Post-rainfall, we show that the dilution-corrected amount of highly aromatic DOM molecular formulae (i.e. those categorised into the groups polyphenolics and condensed aromatics) were 1.7 and 2.0 times higher respectively than in pre-rainfall samples. We attribute this to the flushing of peat-derived DOM from buried organic material into the groundwater. We also identify that periods of low precipitation can lead to low hydrophilic/HOC ratios in groundwater (median = 4.9, n = 14). Redundancy analysis (RDA) was used to compare the HOC fraction with FT-ICR MS compound groups. We show that HOC has a more aromatic character in pre-rainfall samples, and is less similar to the aromatic groups in post-rainfall samples. This suggests that the decline in water-borne hydrophobics observed post-rainfall could be associated with preferential adsorption of the hydrophobic aromatic DOM, making post-rainfall samples less treatable for potable water supply. Post-rainfall we also observe significant increases in arsenic (leading to concentrations greater than 3 times the World Health Organisation drinking water limit of 10 μg / L). Increases in coastal rainfall due to climate change may therefore alter the composition of groundwater DOM in coastal peatland areas in ways that may impact DOM bioavailability, and increase arsenic concentrations, reducing the ease of water treatment for human consumption. To the best of our knowledge, this is the first study to identify the chemical and molecular changes of shallow groundwater DOM pre-rainfall and post-rainfall in a sedimentary organic carbon rich environment through multiple analytical techniques. © 2019 Elsevier Ltd
Changes in hydrology and carbon cycling following Late Holocene deforestation in a New Zealand lake catchment
(European Geosciences Union (EGU), 2018-04-13) Woodward, CA; Hua, Q; Tyler, JJ; Meredith, KT; Moss, PT; Gadd, PS; Zawadzki, A
New Zealand was one of the last major land masses to be impacted by humans, with two waves of settlement occurring in the last 800 years. Polynesian (Maori) settlers arrived in New Zealand ca. 1250 A.D., while major European settlement occurred after 1840 A.D. A major impact of both phases of settlement was clearance of indigenous forest. An increasing number of pollen and macroscopic charcoal records reveal the timing and extent of past forest clearance in New Zealand. Only a few records explore the wider implications of this land use change in terms of catchment biogeochemical cycles and aquatic ecosystem functioning. We used multiple proxies from a lake sediment core from a cleared catchment to explore changes in catchment hydrology and carbon cycling after forest clearance. One of the most interesting findings emerged from paired radiocarbon dates on terrestrial targets (e.g. leaves and charcoal) and seeds from the aquatic plant Myriophyllum. The offset between terrestrial and aquatic radiocarbon ages increased to 1000 years and then decreased to 100 years within three centuries of local Maori forest clearance. There was a further increase in the radiocarbon age offset to 1500 radiocarbon years within decades of the start of the European forest clearance. We argue that the offset between terrestrial and aquatic radiocarbon ages results from an increased contribution of old dissolved inorganic carbon from groundwater to the lake after forest clearance. Forest clearance reduced evapotranspiration, increased aquifer recharge and increased the contribution of groundwater to the lake. This interpretation is supported by a major increase in the δ 13C of Myriophyllum seeds following Maori deforestation. At the time of abstract submission the results are pending for δ 18O analysis on Myriophyllum seeds and aquatic insects. This will provide a further test for changes in catchment hydrology following deforestation. Reviews of catchment impacts on hydrology and carbon cycling have shown an increased catchment water yield and flux of old carbon in disturbed catchments. Our study provides one of the most comprehensive records of forest clearance and provides valuable insights into the causal mechanisms and consequences of these changes. © Author(s) 2018. CC Attribution 4.0 license.
Characterisation and controls on mineral-sorbed organic matter from a variety of groundwater environments
(EarthArXiv, 2019-12-13) Oudone, PP; Rutlidge, H; Andersen, MS; O'Carroll, DM; Cheong, S; Meredith, KT; McDonough, LK; Marjo, CE; Baker, AA
Detailed investigations into natural groundwater organic matter (OM) as carbon sources or sinks in the natural carbon cycle are generally limited. Groundwater OM concentration and composition is altered by biodegradation and sorption to minerals. In the saturated zone of an aquifer, dissolved organic matter (DOM) may represent a significant fraction of the natural groundwater dissolved organic carbon (DOC) pool, therefore understanding how mineral sorption influences OM will contribute to our understanding of how DOC is processed in groundwater. In this study we investigate the dominant fractions of natural DOC in groundwater and the extent of sorption on three common minerals found in the environment: iron-oxide coated sand, calcite and quartz sand. DOM sorption on these minerals was studied using groundwaters from three different geological environments in New South Wales, Australia: Anna Bay (quartz-sand coastal aquifer); Maules Creek (alluvial gravel and clay aquifer); and Wellington (alluvial karst limestone aquifer). Each groundwater and surface sample were characterised before and after sorption using size exclusion liquid chromatography with organic carbon detection (LC-OCD). Analysis revealed that humic substances (HS) are the dominant (13 – 70%) fraction of natural groundwater DOC. HS sorption on iron-oxide coated sand was higher than that on calcite and quartz sand, respectively while sorption on the calcite was also higher than on quartz sand. In shallow-sandy aquifer groundwater, due to less DOC sorption in sandy environment (Anna Bay), DOC concentration was found to be the highest compared to that from karst and other alluvial boreholes from Maules Creek and Wellington. HS sorption increases with the mineral mass and DOC concentration indicating that DOC sorption to the mineral surface did not reach saturation under the study conditions. Only the high-DOC alluvial groundwater produced significant sorption to each mineral phase and of the chemical fractions present (85% of 72 batch systems that HS sorption was found). Multiple linear regression showed that mineral mass, mineral type, depth of groundwater sample, DOC concentration, aqueous Fe2+ concentration and DOM aromaticity are the controlling factors of DOC sorption in the various groundwater environments. The regression analysis showed sorption decreases with depth, which could be because of DOC sorption along the groundwater flow path, resulting in less DOC at depth. The multiple linear regression predicts less DOC (HS) sorption in quartz sand system, agreeing with laboratory sorption results. HS sorption also correlated with aromaticity suggesting the chemical character of HS will control the degree of mineral sorption. The model also indicated that DOC sorption is negatively correlated with dissolved Fe2+ concentration in water samples presumably due to redox condition which is under anoxic environment iron oxide became electron acceptors under the process of DOC biodegradation leaving higher Fe2+ concentration and less available DOC for sorption.
Characterisation of groundwater dissolved organic matter using LC-OCD: implications for water treatment
(Elsevier, 2021-01-01) Rutlidge, H; McDonough, LK; Oudone, PP; Andersen, MS; Meredith, KT; Chinu, K; Peterson, MA; Baker, AA
The polarity and molecular weight of dissolved organic matter (DOM) is an important factor determining the treatability of water for domestic supply. DOM in surface water and groundwater is comprised of a mixture of carbon with varying molecular weight ranges, with its composition driven by DOM sources and processing. Here, we present the largest dataset of chromatographic DOM in surface and groundwater samples (n = 246) using liquid chromatography organic carbon detection (LCsingle bondOCD). Our data represents four categories (surface water, hyporheic zone water, local groundwater, and regional groundwater) from five different sites across Australia. In all environments, high molecular weight hydrophilic DOM such as biopolymers (BP) and humic substances (HS) are present in surface waters and are processed out of groundwater as it moves from surface water and hyporheic zones into shallow local groundwater and deeper regional groundwaters. This results in a higher percentage of low molecular weight neutrals (LMWN) and hydrophobic organic carbon (HOC) in deeper regional groundwaters. Our findings indicate that the presence of sedimentary organic matter strongly influence the character of surface and groundwater DOM, resulting in groundwater with higher HS aromaticity and molecular weight, and reduced percentage of LMWNs. We also observe highly variable hydrophilic / HOC ratios in groundwater at all sites, with 9.60% and 25.64% of samples at sites containing sedimentary peat layers and non-sedimentary peat sites respectively containing only hydrophilic dissolved organic carbon (DOC). We identify average hydrophilic / HOC ratios of 4.35 ± 3.76 and 7.53 ± 5.32 at sites containing sedimentary peat layers and non-sedimentary peat sites respectively where both hydrophilic DOC and HOC are present. Overall our results suggest that fractured rock and alluvial aquifers in sedimentary organic carbon poor environments may contain DOC which is better suited to ozonation, biologically activated carbon filtration powdered activated carbon, suspended ion exchange treatment or magnetic ion exchange resin since DOC is more hydrophilic and of lower molecular weight and lower aromaticity. Aquifers located near sedimentary organic matter layers may benefit from pre-treatment by coagulation/flocculation, sedimentation and sand filtration which have high removal efficiency for high molecular weight and polar compounds. © 2021 Elsevier Ltd.
Characterisation of shallow groundwater dissolved organic matter in aeolian, alluvial and fractured rock aquifers
(Elsevier, 2020-03-15) McDonough, LK; Rutlidge, H; O’Carroll, DM; Andersen, MS; Meredith, KT; Benkhe, MI; Spencer, RGM; McKenna, AM; Marjo, CE; Oudone, PP; Baker, AA
Groundwater organic matter is processed within aquifers through transformations such as the adsorption of dissolved organic matter (DOM) to minerals and biodegradation. The molecular character of DOM varies according to its source and this can impact its bioavailability and reactivity. Whilst the character of DOM in riverine and oceanic environments is increasingly well understood, the sources, character and ultimately the fate of groundwater DOM remains unclear. Here we examine groundwater DOM from contrasting hydrogeological settings in New South Wales, Australia. For the first time, we identify the distinct molecular composition of three groundwater DOM end-members including a modern terrestrial input, an aged sedimentary peat source, and an aged stable by-product pool. We also identify and characterise the processing pathway of DOM in semi-arid, low sedimentary organic carbon (OC) environments. Based on size exclusion chromatography, ultrahigh-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), isotopic analyses (13C, 14C and 3H) and principle component analysis (PCA), we show that in higher rainfall temperate coastal peatland environments, large amounts of aged sedimentary organic carbon can leach into groundwater resulting in higher molecular weight (500 g mol−1 < molecular weight > 1000 g mol−1) and highly aromatic groundwater DOM with high O/C ratios and low H/C ratios. We show that in semi-arid environments with low rainfall rates and high groundwater residence times, groundwater dissolved organic carbon (DOC) is processed into increasingly low molecular weight (<350 g mol−1), low aromaticity DOM with low O/C ratios and high H/C ratios by subsurface processing mechanisms such as biodegradation and adsorption. We provide the first comprehensive study of groundwater DOM characterisation based on multiple analytical techniques, and highlight the impact of source inputs and processing on groundwater DOM composition at a molecular level. Crown Copyright © 2020 Published by Elsevier Ltd
Characterisation of the Yarragadee aquifer - Northern Perth Basin, Western Australia
(International Association of Hydrogeologists, 2013-09-19) Schafer, D; Kern, A; Meredith, KT
The Yarragadee aquifer in the Northern Perth Basin near Geraldton in Western Australia has been characterised using a variety of groundwater investigation techniques to enable better aquifer management for town water supply, industrial and agricultural usages. New structural contour surfaces and sand percentage maps for aquifer layers have been generated using borehole gamma and lithology data from over 200 bores (including 27 new bores). 3-D salinity distribution maps have been developed using correlations with borehole resistivity, airborne transient electromagnetic (TEM) data and borehole salinity measurements. Groundwater chemistry, stable isotopes (δ18/16O and δ2H0) and radiocarbon (14CDIC) data collected from 45 bores was used to characterise localised shallow and sub-regional groundwater-flow systems. Detailed hydrographs were prepared using data-loggers that recorded water level at hourly intervals to understand groundwater recharge dynamics. Localised shallow groundwater in the study area was found to be fresh (<1000 mg/L TDS) and relatively young (~1.5 to 7.0 ka) and in contrast, the deeper sub-regional groundwater was more saline (~ 2000 to 7000 mg/L TDS) and older (>9 ka). Recharge rates for the localised shallow groundwater were found to be much higher than sub-regional groundwater. The influence of faults on groundwater flow is demonstrated by conductivity contrasts observed across faults along TEM flight lines. Stable isotope data indicates that all groundwater is meteoric in origin and Na-Cl type waters dominate the area. Water level rises of around 10 m have been observed in upland areas since a major period of land clearing took place in the 1960s and 1970s. Post-clearing recharge rates have been estimated to be approximately double those of pre-clearing recharge rates. Significant salt input has been inferred to be incorporated during recharge of the sub-regional groundwater which occurs further inland and higher in the landscape. The localised shallow groundwater is fresher, likely because higher recharge and groundwater-ow rates dilute the salt input from rainfall. The improve understanding of recharge, groundwater flow and the source of groundwater salinity will enable the reassessment of available groundwater in the Yarragadee aquifer near Geraldton to be undertaken.
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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