Browsing by Author "Andersen, MS"
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- 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
- 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
- ItemCarbon 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, VEAThis 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
- ItemCarbon 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, VEAThis 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.
- ItemCave monitoring to constrain the paleoclimate interpretation of δ18O proxy in speleothems from semi-arid areas(University of New South Wales and Australian Nuclear Science and Technology Organisation, 2015-07-09) Markowska, M; Baker, AA; Andersen, MS; Jex, CN; Cuthbert, MO; Rau, GC; Graham, PW; Rutlidge, H; Mariethoz, G; Marjo, CE; Treble, PC; Edwards, NNot supplied to the ANSTO Library.
- ItemCave stalagmites as records of past recharge frequency in semi-arid Australia(National Centre for Groundwater Research And Training, 2015-11-03) Markowska, M; Baker, AA; Andersen, MS; Rutlidge, H; Jex, CN; Cuthbert, MO; Rau, GC; Adler, L; Graham, PW; Mariethoz, G; Marjo, CE; Treble, PCUnderstanding past variability in groundwater recharge over recent time scales (0 – 10 ka) in Australia is essential for future sustainable groundwater management in a changing climate. Currently, there are limited data about past infiltration rates and their relationship to environmental controls that dominate recharge variability. Speleothem (cave precipitates) records may provide a new approach to understanding past infiltration (i.e. recharge rates), in addition to traditional interpretations of connectivity between climate and the hydrological cycle, in drier parts of Australia. In this study we used Cathedral Cave, (SE Australia) located in a temperate semi-arid climate, as a natural laboratory to investigate cave infiltration rates and the climate-karst-cave interactions driving the isotopic (δ18O) and chemical variability in modern drip water. These findings were then used to interpret the δ18O stalagmite record from two modern speleothems growing during the last ~50 years. Modern drip water results showed that the δ18O composition was enriched by up to 2.77 ‰ relative to annually weighted mean rainfall. Isotopically lighter δ18O occurred during infiltration events, followed by subsequent isotopic enrichment as evaporation in the unsaturated zone fractionated δ18O of stored water. Drip rate monitoring revealed that larger events leading to infiltration were infrequent (0 – 3 a-1) and the ‘effectiveness’ of these infiltration events was controlled by antecedent moisture conditions in the soil zone. In drier climatic zones, evaporation drives the enrichment of δ18O in the unsaturated zone, allowing periods of infiltration to be identified from the stable isotopic composition of drip waters. Our findings are important for interpreting speleothem records from regions with infrequent recharge and high evaporation rates. Such records are likely to contain evidence of past infiltration events moderated by an evaporation signal, allowing records of paleo-recharge to be reconstructed for drier climate regions of Australia.
- ItemCaves: observatories of Australia’s diffuse groundwater recharge history(National Centre for Groundwater Research And Training, 2015-11-03) Baker, AA; Treble, PC; Andersen, MS; Markowska, M; Coleborn, K; Flemons, I; Kempsey Speleological SocietyQuantifying the timing and extent of diffuse groundwater recharge is crucial for our understanding of groundwater recharge processes. However, diffuse recharge is notably difficult to quantify. Our novel approach is to use caves as natural observatories of the diffuse recharge process, with the aim of improving our understanding of diffuse recharge in the context of climate change and climate variability. Since 2010, funded by the NCRIS Groundwater Infrastructure project, researchers from UNSW and ANSTO have established a long-term, national monitoring program of infiltration into caves using automated loggers. Five karst regions, in semi-arid, temperate, subtropical and montane climates from southwest WA to the mid- north coast of NSW, have been instrumented with automatic infiltration loggers. Over 200 loggers (between 10 and 40 per cave) have collected data on the timing and amount of diffuse recharge, from sites of contrasting limestone geology, starting in 2010. We present empirical data on the timing and relative amounts of diffuse recharge from 2010 to present. Caves with a range of depths from 0-40m show decreasing frequency of diffuse recharge events with depth below ground surface. Event-based rainfall intensity is confirmed to be the primary driver of diffuse groundwater recharge at all fractured rock sites, whereas annual rainfall amount is the primary driver at a site with high primary porosity. Inter-annual variability in the frequency and relative amount of recharge is compared to climate forcing variables such as the ENSO and surface temperature. Groundwater recharge is via both direct (river recharge) and diffuse processes. With anthropogenic global warming, increased temperatures will increase evaporation, and will likely change ENSO patterns, both of which will affect diffuse groundwater recharge. Our cave observatory system helps improve our understanding of the diffuse recharge process and provides a baseline monitoring network during a period of climate change.
- ItemChanges 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, AAClimate 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)
- ItemChanges 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, AADissolved 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
- ItemCharacterisation 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, AADetailed 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.
- ItemCharacterisation 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, AAThe 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.
- ItemCharacterisation 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, AAGroundwater 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
- ItemClimate and groundwater recharge: the story from Australian caves(National Centre for Groundwater Research And Training, 2017-07-11) Baker, AA; Treble, PC; Markowska, M; Andersen, MS; Wang, Z; Mahmud, K; Cuthbert, MO; Coleborn, K; Rau, GCQuantifying the timing and extent of diffuse groundwater recharge is crucial for our understanding of groundwater recharge processes. However, diffuse recharge is notably difficult to measure directly. Caves can be used as natural observatories of ongoing diffuse recharge processes, and speleothems (cave carbonate deposits such as stalagmites) as archives of past recharge. Cave records can improve our understanding of diffuse recharge in the context of climate change and past climate variability. A long-term, national monitoring program of infiltration into caves has been undertaken since 2010 using a network of over 200 automated loggers. This has been supplemented by artificial irrigation experiments at one semi-arid site. The timing of past recharge can be determined from the periods of past stalagmite growth. Recharge characteristics can be elucidated from oxygen isotope composition, with increased 18O likely caused by evaporative fractionation and increased 16O from high intensity/magnitude rainfall events. Automated logger data identify the diffuse recharge thresholds that vary with climate and geology. Both the logged data of natural events and the artificial irrigation experiments identify significant spatial heterogeneity in recharge in these karstified systems. Water infiltrating into the karst is often depleted in the lighter oxygen isotope due to soil and shallow subsurface evaporative fractionation. Speleothem deposition is more frequent during glacial periods, presumably because recharge thresholds are lower, and their isotopic composition provides evidence of the characteristics of the recharge process. Caves provide direct access into the unsaturated zone. Direct observation of groundwater recharge can be used to complement data from the saturated zone (boreholes) and models. The heterogeneity of recharge in karst aquifers can be directly observed and quantified. Speleothems preserve a record of groundwater recharge that can extend back for hundreds of thousands of years, providing a long-term view on the timing and variability of groundwater recharge in Australia.
- ItemCombustion completeness and sample location determine wildfire ash leachate chemistry(American Geophysical Union, 2024-05-21) Campbell, M; Treble, PC; McDonough, LK; Naeher, S; Baker, AA; Grierson, PF; Wong, HKY; Andersen, MSUnderstanding past fire regimes and how they vary with climate, human activity, and vegetation patterns is fundamental to the mitigation and management of changing fire regimes as anthropogenic climate change progresses. Ash‐derived trace elements and pyrogenic biomarkers from speleothems have recently been shown to record past fire activity in speleothems from both Australia and North America. This calls for an empirical study of ash geochemistry to aid the interpretation of speleothem palaeofire proxy records. Here we present analyses of leached ashes collected following fires in southwest and southeast Australia. We include a suite of inorganic elemental data from the water‐soluble fraction of ash as well as a selection of organic analytes (pyrogenic lipid biomarkers). We also present elemental data from leachates of soils collected from sites in southwest Australia. We demonstrate that the water‐soluble fraction of ash differs from the water‐soluble fraction of soils, with trace and minor element concentrations in ash leachates varying with combustion completeness (burn severity) and sample location. Changes in some lipid biomarker concentrations extracted from ashes may reflect burn severity. Our results contribute to building a process‐based understanding of how speleothem geochemistry may record fire frequency and severity, and suggest that more research is needed to understand the transport pathways for the inclusion of pyrogenic biomarkers in speleothems. Our results also demonstrate that potential contaminant loads from ashes are much higher than from soils, with implications for the management of karst catchments, which are a critical water resource. © 2024 The Author(s). Geochemistry,Geophysics, Geosystems published by Wiley Periodicals LLC on behalf of American Geophysical Union. This is an open access article under the terms of the Creative Commons Attribution License, which permits use,distribution and reproduction in any medium, provided the original work is properly cited
- ItemConstraining water fluxes through the streambed of a semi-arid losing stream using natural tracers: heat and radioisotopes(American Geophysical Union, 2011-12-05) Andersen, MS; Rau, GC; McCallum, AM; Meredith, KT; Acworth, RINatural physical and chemical tracers of flow have different advantages and shortfalls based on their properties and the uncertainty related to variability in their source concentration. Each tracer integrates over a characteristic spatial-temporal scale depending on its decay or production rate and the flow velocity of the system. For instance heat tracing using diurnal temperature fluctuations will, at best, provide information about flow in the upper 1-2 m of the streambed before the signal is dampened below measurement resolution (Constantz et al. 2003). Conversely, radioisotopes used as tracers will integrate over increasing spatio-temporal scales for decreasing decay constants. Radioisotopes with comparatively slow decay rates will be less sensitive for resolving flow conditions on short spatio-temporal scales. Therefore, it is difficult to use these tracers in the streambed of losing systems because the radioactive decay is not discernible against the variability. Consequently, employing a combination of different tracers provides information on different parts of a given flow system. Comparing flow velocities derived from tracers integrating over different scales allows for separating the local hyporheic exchange from the regional groundwater recharge. A field experiment was carried out in a perennial section of the mostly ephemeral Maules Creek in NSW, Australia. Streambed temperature profiles were monitored at three sites along a 400 m stretch of the perennial reach. Streambed temperatures were recorded at 4 depths within one meter below the streambed. Water samples were collected from surface water, streambed and groundwater and analysed for stable water isotopes (18O and 2H) and radioisotopes (222Rn and 3H). The streambed heat profiles provided time series of surface water/groundwater exchange. Using this method it was found that the conditions were losing at all three sites with recharge rates varying between 0 and 0.4 m/d. 222Rn measurements in the surface water along the perennial reach qualitatively identified losing and gaining sections of the stream with low and high 222Rn activities, respectively. One of the losing sections of the stream was instrumented with a transect of groundwater piezometers. In this transect, 3H levels of 1.3-1.5 TU were measured, comparable to surface waters, indicating recent groundwater recharge. However, the variations in 3H combined with the analysis uncertainty did not allow for a recharge estimate. 222Rn with its half-life of only 3.8 d proved more useful. A zone of low 222Rn activity was found as deep as 6-7 m below the stream, corroborating the 3H and temperature data. Regional groundwater 222Rn activities were used to estimate the secular equilibrium activity of Rn. Residence times of 1 to 7 days were calculated based on these estimates. Converted to Darcy velocities of 0.2-1.7 m/d these values generally agree with the velocities derived from the temperature data indicating that the measured fluxes from the temperature data represent recharge rates and not simply hyporheic exchange. © American Geophysical Union.
- ItemDissolved organic matter (DOM) concentration and quality in a coastal aquifer(Copernicus Publications, 2015-04-14) Zainuddin, NS; Andersen, MS; Baker, AA; Howley, EM; O'Carroll, DM; Jex, CN; Meredith, KT; Wells, EThis study investigates the range of fluorescence properties of natural occurring DOM in a coastal aquifer at Anna Bay, NSW, Australia. The determination of the extent to which DOM varies in coastal groundwater has been distinguished through fluorescence spectroscopy by excitation-emission matrices (EEM), and the application of parallel factor analysis (PARAFAC). In addition, DOM was characterised by a combination of DOC-LABOR Liquid Chromatography - Trace Organic Carbon Detector (LC-OCD) method and PHREEQC modelling. In general, results show an anoxic aquifer featuring calcite dissolution in the upper regions of the aquifer and organic matter degradation with redox zonation dominated by iron and sulphate reduction as well as methanogenesis. Several fluorescence EEM patterns were identified. DOM in coastal environment was variable, but mainly composed of low molecular weight compounds. On overall system two humic-like substances (C1, C2) and one fulvic-like substance (C3) were identified by the PARAFAC model. C1 and C2 exhibited same trends and were very similar. Measurement of the fluorescence excitation-emission matrices (EEM) and subsequent PARAFAC reveal different fluorescent DOM fractions and hence variable contributions by DOM to the reduction process in the coastal aquifer zones. © 2015 The Author(s).
- ItemDissolved organic matter in the unsaturated zone: the view from the cave(American Geophysical Union (AGU), 2017-12-14) Baker, AA; Duan, W; Rutlidge, H; McDonough, LK; Oudone, PP; Meredith, KT; Andersen, MS; O'Carroll, DM; Coleborn, K; Treble, PCSoil organic matter content is typically a few percent of the total soil composition. Diffuse recharge can mobilise some of this soil-derived organic matter. While soil pore water dissolved organic matter (DOM) concentrations are up to 100 ppm, the resulting groundwater dissolved organic matter concentration is typically less than 2ppm. Dissolved organic matter transported from the soil can be both biodegraded and sorbed to minerals, and the relative importance of these two processes in the unsaturated zone is poorly understood. Caves in karstified limestone uniquely provide direct access to water percolating from the soil to the groundwater. Cave percolation waters can be analysed for their DOM concentration and character. This provides insights into the extent and type of biological and chemical processing of DOM during transport from the soil to the groundwater. We determine the concentration and characteristics of DOM in cave percolation waters using liquid chromatography (LC-OCD) and optical spectrophotometry (fluorescence and absorbance). We sample DOM from multiple caves in SE Australia (Cathedral Cave, Wellington; South Glory and Harrie Wood Caves, Yarrangobilly), permitting comparison of unsaturated zone DOM properties at different depths (up to 30m below land surface) and different climate zones (montane and temperate). We use caves with long-term hydrological monitoring programs so that DOM in waters of contrasting residence times can be compared. Additionally, we compare these cave percolation water DOM characteristics to those from local and regional groundwater, sampled from nearby wells. Our results will help improve our understanding of how DOM is processed from soil to groundwater, and is also relevant to speleothem scientists interested in using organic matter preserved in speleothems as a paleoclimate or paleoenvironmental proxy. Plain Language Summary When plants die, they break down to organic matter, which forms part of the soil. When this organic matter is washed out of the soil and into the subsurface, we know very little about what happens next. Partly it is because we can't see and measure what is happening. There is a solution. We can use caves as observatories. We can collect the organic matter in the water which enters the caves, and analyse it back in the laboratory. There, we can determine not only the cocntration of organic matter, but also its chemical composition. Why is this important? There's lot of organic matter in soil. But only one or two organic molecues per million water molecules are present in groundwater. Where does it all go? One idea is that it is used as food by subterranean microbes. Another is that is sorbed to minerals. By measuring the chemical composition of organic matter in cave drip waters, we can work out which is more important, and help understand why there is so little organic matter in groundwater.
- ItemDrip hydrology monitoring in caves to inform stalagmite palaeoclimate records, Yarrangobilly, NSW(Australasian Quaternary Association Inc, 2014-01-01) Markowska, M; Treble, PC; Baker, AA; Andersen, MS; Hankin, SIPalaeoclimate research using speleothems has significantly increased over the last decade, owing to their potential to provide multi-proxy high resolution (sub-annual) terrestrial records of past climate variability. A crucial step in using these archives as high resolution proxies is understanding the connectivity between the surface climate and the signal transferred to the speleothem. This study investigates the modern karst hydrology at Yarrangobilly Caves, in the Snowy Mountains NSW. A high-frequency, spatially-dense drip water monitoring campaign in Harrie Wood Cave, was conducted over a 13 month period to characterise the hydrology of 14 sites within the same cave. By utilising the cave as a natural observatory we can determine 1) vadose-zone flow regimes, and 2) thresholds of recharge at the site. Using a statistical approach (PCA and AHC) 5 main drip hydrological regimes were established. Depth was found to have a moderate relationship (r2 = 0.4) with discharge, whereby increasing depth was associated with a dampening of flow and drip response. However, depth could not account for all the variability observed in the drip hydrology, suggesting complex controls unrelated to depth, such as unsaturated zone storage and mixing, appear to have a significant impact on vadose-zone flow regimes. As a speleothem is a function of the infiltrating drip water, we suggest that stalagmites fed by different drip types may thus contain different parts of the climate record i.e. smoothed mean annual vs. an extreme event record. These findings will be used to assess three suitable stalagmites for palaeoclimate reconstruction, fed by drip waters with different hydrological regimes and the preliminary results presented here. © Australasian Quaternary Association Inc.
- ItemDrip water isotopes in semi-arid karst: implications for speleothem paleoclimatology(Elsevier Science BV, 2014-06-01) Cuthbert, MO; Baker, AA; Jex, CN; Graham, PW; Treble, PC; Andersen, MS; Acworth, RIWe report the results of the first multi-year monitoring and modelling study of the isotopic composition of drip waters in a semi-arid karst terrane. High temporal resolution drip rate monitoring combined with monthly isotope drip water and rainfall sampling at Cathedral Cave, Australia, demonstrates that drip water discharge to the cave occurs irregularly, and only after occasional long duration and high volume rainfall events, where the soil moisture deficit and evapotranspiration is overcome. All drip waters have a water isotopic composition that is heavier than the weighted mean annual precipitation, some fall along the local meteoric water line, others trend towards an evaporation water line. It is hypothesised that, in addition to the initial rainfall composition, evaporation of unsaturated zone water, as well as the time between infiltration events, are the dominant processes that determine infiltration water isotopic composition. We test this hypothesis using a soil moisture balance and isotope model. Our research reports, for the first time, the potential role of sub-surface evaporation in altering drip water isotopic composition, and its implications for the interpretation of speleothem delta O-18 records from arid and semi-arid regions. © 2014, Elsevier Ltd.
- ItemDripwater organic matter and trace element geochemistry in a semi-arid karst environment: Implications for speleothem paleoclimatology(Elsevier, 2014-06-15) Rutlidge, H; Baker, AA; Marjo, CE; Andersen, MS; Graham, PW; Cuthbert, MO; Jex, CN; Rau, GC; Roshan, H; Markowska, M; Mariethoz, GA series of four short-term infiltration experiments which revealed hydrochemical responses relevant to semi-arid karst environments were carried out above Cathedral Cave, Wellington, New South Wales (NSW), Australia. Dripwater samples were collected at two sites for trace element and organic matter analysis. Organic matter was characterised using fluorescence and interpreted using a PARAFAC model. Three components were isolated that represented unprocessed, soil-derived humic-like and fulvic-like material, processed humic/fulvic-like material and tryptophan-like fluorescence. Principal Component Analysis (PCA) performed on the entire dataset comprising trace element concentrations and PARAFAC scores revealed two dominant components that were identified as soil and limestone bedrock. The soil component was assigned based on significant contributions from the PARAFAC scores and additionally included Ba, Cu, Ni and Mg. The bedrock component included the expected elements of Ca, Mg and Sr as well as Si. The same elemental behaviour was observed in recent stalagmite growth collected from the site. Our experiments demonstrate that existing paleoclimate interpretations of speleothem Mg and Sr, developed in regions of positive water balance, are not readily applicable to water limited environments. We provide a new interpretation of trace element signatures unique to speleothems from water limited karst environments. © 2014, Elsevier Ltd.