Browsing by Author "Fairchild, IJ"
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- ItemEight-years of cave monitoring at Golgotha Cave, SW Australia: implications for speleothem paleoclimate records(Australasian Quaternary Association Inc, 2014-06-29) Treble, PC; Fairchild, IJ; Baker, AA; Bradley, C; Wood, A; McGuire, ESpeleothems are an important archive of paleoenvironmental information but a thorough understanding of processes are necessary for their interpretation. In order to better understand speleothem records from the climatically-sensitive southwest region of WA, we have conducted a detailed eight-year monitoring study at Golgotha Cave, southwest WA. Oxygen isotopic data demonstrated that the majority of water moved through the porous Quaternary calcarenite as matrix-flow with an inferred transit time of <1 year. A zone of high-flow dripwater is fed by high-magnitude rainfall events (Treble et al., 2013). Prior calcite precipitation (PCP) signals of increased Mg/Ca and Sr/Ca in dripwater are attributed to stalactite deposition. This signal is enhanced at low-flow sites and minimised at the high-flow site as degassing and subsequent stalactite deposition are a function of drip interval. Long-term rising trends found in most solutes are attributed via a mass-balance approach to increasing forest bioproductivity, consistent with an increase in forest understorey following a low-intensity burn in 2006. A fundamental message from this study is that individual speleothem records from within Golgotha Cave will differ, e.g. speleothem δ18O at our high-flow site is biased to recording high-magnitude rainfall events, whilst PCP will be the main driver of speleothem Mg/Ca and Sr/Ca at low-flow sites. Forest biomass appears to be modulating transpiration-sensitive ions and these may serve as an indicator of fire history.
- ItemENSO–cave drip water hydrochemical relationship: a 7-year dataset from south-eastern Australia(2020-05-26) Tadros, CV; Treble, PC; Baker, AA; Fairchild, IJ; Hankin, SI; Roach, R; Markowska, M; McDonald, JSpeleothems (cave deposits), used for palaeoenvironmental reconstructions, are deposited from cave drip water. Differentiating climate and karst processes within a drip-water signal is fundamental for the correct identification of palaeoenvironmental proxies and ultimately their interpretation within speleothem records. We investigate the potential use of trace element and stable oxygen-isotope (δ18O) variations in cave drip water as palaeorainfall proxies in an Australian alpine karst site. This paper presents the first extensive hydrochemical and δ18O dataset from Harrie Wood Cave, in the Snowy Mountains, south-eastern (SE) Australia. Using a 7-year long rainfall δ18O and drip-water Ca, Cl, Mg / Ca, Sr / Ca and δ18O datasets from three drip sites, we determined that the processes of mixing, dilution, flow path change, carbonate mineral dissolution and prior calcite precipitation (PCP) accounted for the observed variations in the drip-water geochemical composition. We identify that the three monitored drip sites are fed by fracture flow from a well-mixed epikarst storage reservoir, supplied by variable concentrations of dissolved ions from soil and bedrock dissolution. We constrained the influence of multiple processes and controls on drip-water composition in a region dominated by El Niño–Southern Oscillation (ENSO). During the El Niño and dry periods, enhanced PCP, a flow path change and dissolution due to increased soil CO2 production occurred in response to warmer than average temperatures in contrast to the La Niña phase, where dilution dominated and reduced PCP were observed. We present a conceptual model, illustrating the key processes impacting the drip-water chemistry. We identified a robust relationship between ENSO and drip-water trace element concentrations and propose that variations in speleothem Mg / Ca and Sr / Ca ratios may be interpreted to reflect palaeorainfall conditions. These findings inform palaeorainfall reconstruction from speleothems regionally and provide a basis for palaeoclimate studies globally, in regions where there is intermittent recharge variability. © Author(s) 2016.
- ItemHydrological and geochemical responses of fire in a shallow cave system(2019-04-20) Bian, F; Coleborn, K; Flemons, I; Baker, AA; Treble, PC; Hughes, CE; Baker, AC; Andersen, MS; Tozer, MG; Duan, WH; Fogwill, CJ; Fairchild, IJThe influence of wildfire on surface soil and hydrology has been widely investigated, while its impact on the karst vadose zone is still poorly understood. A moderate to severe experimental fire was conducted on a plot (10 m × 10 m) above the shallow Wildman's Cave at Wombeyan Caves, New South Wales, Australia in May 2016. Continuous sampling of water stable isotopes, inorganic geochemistry and drip rates were conducted from Dec 2014 to May 2017. After the fire, drip discharge patterns were significantly altered, which is interpreted as the result of increased preferential flows and decreased diffuse flows in the soil. Post-fire drip water δ18O decreased by 6.3‰ in the first month relative to the average pre-fire isotopic composition. Post-fire monitoring showed an increase in drip water δ18O in the following six months. Bedrock related solutes (calcium, magnesium, strontium) decreased rapidly after the fire due to reduced limestone dissolution time and potentially reduced soil CO2. Soil- and ash-derived solutes (boron, lead, potassium, sodium, silicon, iodine and iron) all decreased after the fire due to volatilisation at high temperatures, except for SO42−. This is the first study to understand the hydrological impact from severe fires conducted on a karst system. It provides new insights on the cave recharge process, with a potential explanation for the decreased d18O in speleothem-based fire study, and also utilise the decreased bedrock solutes to assess the wildfire impacts both in short and long time scales. Open access © 2021 Elsevier B.V
- ItemThe impact of fire on the geochemistry of speleothem-forming drip water in a sub-alpine cave(Elsevier, 2018-11) Coleborn, K; Baker, AA; Treble, Pauline C; Andersen, MS; Baker, AC; Tadros, CV; Tozer, MG; Fairchild, IJ; Spate, A; Meehan, SFire dramatically modifies the surface environment by combusting vegetation and changing soil properties. Despite this well-documented impact on the surface environment, there has been limited research into the impact of fire events on karst, caves and speleothems. Here we report the first experiment designed to investigate the short-term impacts of a prescribed fire on speleothem-forming cave drip water geochemistry. Before and after the fire, water was collected on a bi-monthly basis from 18 drip sites in South Glory Cave, New South Wales, Australia. Two months post-fire, there was an increase in B, Si, Na, Fe and Pb concentrations at all drip sites. We conclude that this response is most likely due to the transport of soluble ash-derived elements from the surface to the cave drip water below. A significant deviation in stable water isotopic composition from the local meteoric water line was also observed at six of the sites. We hypothesise that this was due to partial evaporation of soil water resulting in isotopic enrichment of drip waters. Our results demonstrate that even low-severity prescribed fires can have an impact on speleothem-forming cave drip water geochemistry. These findings are significant because firstly, fires need to be considered when interpreting past climate from speleothem δ18O isotope and trace element records, particularly in fire prone regions such as Australia, North America, south west Europe, Russia and China. Secondly, it supports research that demonstrates speleothems could be potential proxy records for past fires. © 2018 Elsevier B.V.
- ItemThe impact of wildfire on the geochemistry and hydrology the vadose zone(National Centre for Groundwater Research And Training, 2017-07-12) Coleborn, K; Baker, AA; Treble, PC; Baker, AC; Andersen, MS; Tozer, MG; Fairchild, IJ; Spate, A; Meehan, SWildfire can dramatically modify the surface environment by removing surface vegetation, killing microbial communities and changing the soil geochemical and physical structure. Wildfires are a widespread phenomenon in Australia with 87,810 ha burnt in 2015-2016 in NSW alone (New South Wales Rural Fire Service, 2016). However, there has been little research on the impact of wildfire on vadose zone hydrology in Australia or elsewhere. Limestone caves can be used as natural laboratories to study the impact of the surface environment on vadose zone hydrology in real time. We conducted a two year monitoring program to examine the short term (less than one year) post-fire impacts on the geochemistry and hydrology of vadose zone water in Glory Hole Cave, Kosciuszko National Park, NSW. We ignited an experimental wildfire on the surface over the cave after 1 year of monitoring and compared the pre- and post-fire data. The findings indicate that there is a short term post-fire response in the organic and inorganic geochemistry vadose zone water. There was a post-fire spike in dissolved organic carbon, dominated by the hydrophilic fraction more than one month post-fire which was most likely due to high influx of ash from the fire. There was a multi-month increase in organic-associated metals such as Cu and Zn. The concentration of trace metals such as Fe and Si increased by an order of magnitude less than three months post-fire and was attributed to a flush of small colloidal organic matter. This study enabled us to establish that there is an organic and inorganic cave vadose zone water response to wildfires. The findings of this study can inform fire management strategies in order to protect sensitive karst environments in addition to water resource managers concerned with fluxes of mobilised metals nutrient fluxes to the vadose zone.
- ItemImpacts of cave air ventilation and in-cave prior calcite precipitation on Golgotha Cave dripwater chemistry, southwest Australia(Elsevier, 2015-11) Treble, PC; Fairchild, IJ; Griffiths, AD; Baker, AA; Meredith, KT; Wood, A; McGuire, ESpeleothem trace element chemistry is an important component of multi-proxy records of environmental change but a thorough understanding of hydrochemical processes is essential for its interpretation. We present a dripwater chemistry dataset (PCO2, alkalinity, Ca, SIcc, Mg and Sr) from an eight-year monitoring study from Golgotha Cave, building on a previous study of hydrology and dripwater oxygen isotopes (Treble et al., 2013). Golgotha Cave is developed in Quaternary aeolianite and located in a forested catchment in the Mediterranean-type climate of southwest Western Australia. All dripwaters from each of the five monitored sites become supersaturated with respect to calcite during most of the year when cave ventilation lowers PCO2 in cave air. In this winter ventilation mode, prior calcite precipitation (PCP) signals of increased Mg/Ca and Sr/Ca in dripwater are attributed to stalactite deposition. A fast-dripping site displays less-evolved carbonate chemistry, implying minimal stalactite growth, phenomena which are attributed to minimal degassing because of the short drip interval (30 s). We employ hydrochemical mass-balance modelling techniques to quantitatively investigate the impact of PCP and CO2 degassing on our dripwater. Initially, we reverse-modelled dripwater solutions to demonstrate that PCP is dominating the dripwater chemistry at our low-flow site and predict that PCP becomes enhanced in underlying stalagmites. Secondly, we forward-modelled the ranges of solution Mg/Ca variation that potentially can be caused by degassing and calcite precipitation to serve as a guide to interpreting the resulting stalagmite chemistry. We predict that stalagmite trace element data from our high-flow sites will reflect trends in original dripwater solutes, preserving information on biogeochemical fluxes within our system. By contrast, stalagmites from our low-flow sites will be dominated by PCP effects driven by cave ventilation. Our poorly karstified system allows us to highlight and quantify these in-cave (PCP) processes, which are otherwise masked at sites where karstification is more developed and hydrogeology is more complex. Our modelling also shows enhanced CO2 source production in the unsaturated zone that is attributed to deeply-rooted vegetation and increasing bioproductivity which we link to forest recovery after fires impacted our site during 2006 CE. Crown Copyright © 2015 Published by Elsevier Ltd.
- ItemInterpreting past climate using southwest Australian speleothems(Australian Meterological & Oceanographic Society, 2012-01-31) Treble, PC; Azcurra, CS; Baker, AA; Bradley, C; Wood, A; Fischer, MJ; Fairchild, IJ; Hellstrom, JC; Gagan, MKThere is an identified need to extend our baseline climate information beyond the relatively short duration of instrumental records in Australia. An improved knowledge of natural rainfall variability would assist in our understanding of climate change. SW Australia (SWWA) is one region that has been identified as having a changing climate since the 1970s. Speleothems (cave stalagmites) are an effective archive of past climate variability and caves from the coastal region of SWWA are being studied for paleoclimate records. The modern speleothem record from this region has been assessed and shown to record the post-1970s rainfall decrease (Treble et al., 2003; 2005; Fischer and Treble, 2008). The extension of the speleothem record is currently underway, however, a long-term cave monitoring program was also deemed necessary to separate the climatic from non-climatic signals i.e. to reduce uncertainty when interpreting these records. This presentation outlines what we have learnt about the possible hydrological modification of the climate signal in speleothems. In particular, we present results from a five-year long monitoring study of rainfall and cave drip water O isotopes (!18O) from Golgotha Cave, SWWA. From this study, we have been able to characterize the probable flow paths feeding stalagmites in our monitored cave. These flow paths range from slow diffuse flow of isotopically-averaged rainfall to preferential routing of high-magnitude, 18O-depleted, events along fast flow routes into the cave. Hence, we offer a possible explanation for why paleoclimate records from coeval speleothems in our cave may differ. Our study suggests that this disagreement may simply be due to different flow paths resulting in a bias towards the preservation of high or low magnitude rainfall events.
- ItemAn isotopic and modelling study of flow paths and storage in quaternary calcarenite, SW Australia: implications for speleothem paleoclimate records(Elsevier, 2013-03-15) Treble, PC; Bradley, C; Wood, A; Baker, AA; Jex, CN; Fairchild, IJ; Gagan, MK; Cowley, J; Azcurra, CSWe investigated the distinctive shallow sub-surface hydrology of the southwest Western Australia (SWWA) dune calcarenite using observed rainfall and rainfall δ18O; soil moisture, cave drip rate and dripwater δ18O over a six-year period: August 2005–March 2012. A lumped parameter hydrological model is developed to describe water fluxes and drip δ18O. Comparison of observed data and model output allow us to assess the critical non-climatic karst hydrological processes that modify the precipitation δ18O signal and discuss the implications for speleothem paleoclimate records from this cave and those with a similar karst setting. Our findings include evidence of multiple reservoirs, characterised by distinct δ18O values and recharge responses (‘low’ and ‘high’ flow sites). Dripwaters exhibit δ18O variations in wet versus dry years at low-flow sites receiving diffuse seepage from the epikarst with an attenuated isotopic composition that approximates mean rainfall. Recharge from high-magnitude rain events is stored in a secondary reservoir which is associated with high-flow dripwater that is 1‰ lower than our monitored low-flow sites (δ18O). One drip site is characterised by mixed-flow behaviour and exhibits a non-linear threshold response after the cessation of drainage from a secondary reservoir following a record dry year (2006). Additionally, our results yield a better understanding of the vadose zone hydrology and dripwater characteristics in Quaternary age dune limestones. We show that flow to our monitored sites is dominated by diffuse flow with inferred transit times of less than one year. Diffuse flow appears to follow vertical preferential paths through the limestone reflecting differences in permeability and deep recharge into the host rock. © 2013, Elsevier Ltd.
- ItemAn isotopic and modelling study of recharge to the Tamala Limestone, SW Australia: implications for speleothem paleoclimate records(International Association of Hydrogeologists, 2013-09-20) Treble, PC; Bradley, C; Fairchild, IJ; Baker, AA; Jex, CN; Azcurra, CS; Wood, AWe present a modern calibration of recharge pathways in the vadose zone of Quaternary dune calcarenite (Tamala Limestone in the Margaret River region, SW Western Australia. This study aimed to i. better understand groundwater recharge in these calcarenites, which has wider relevance to SW WA calcarenites and their use as a groundwater source; and to ii. interpret the O isotopic composition of these waters in order to assess the suitability of Golgotha Cave for reconstructing records of paleoclimate using speleothems. We present six years of data from our monitored site at Golgotha Cave (Treble et al. 2013). A lumped parameter hydrological model is developed to describe water fluxes and dripwater O isotopic composition. Comparison of observed data and model output allow us to assess the critical non-climatic karst hydrological processes that modify the precipitation isotopic signal and discuss the implications for speleothem records from this cave and those with a similar karst setting. Our findings include evidence of multiple reservoirs, characterised by distinct isotopic values and recharge responses ('low’ and ‘high’ flow sites). Dripwaters exhibit isotopic variations in wet versus dry years at low-flow sites receiving diffuse seepage from the epikarst with an attenuated isotopic composition that approximates mean rainfall. Recharge from high-magnitude rain events is stored <1%o lower in a secondary reservoir which is associated with high-flow dripwater that is 1%o lower than our monitored low-ow sites. One drip site is characterised by mixed-flow behaviour and exhibits a non-linear threshold response after the cessation of drainage from a secondary reservoir following a record dry year (2006). We show that ow to our monitored sites is dominated by diffuse ow with inferred transit times of less than one year. Diffuse flow appears to follow vertical preferential paths through the limestone reflecting differences in permeability and deep recharge into the host rock. Reference Treble et al. (Z013). An isotopic and modelling study of flow paths and storage in Quaternary calcarenite, SW Australia: implications for speleothem paleoclimate records, Quaternary Science Reviews 64; 90-103.
- ItemPast hydroclimatic variability from southwest Australian speleothems during the last millennium(Australiasian Quaternary Association Inc., 2018-12-10) Treble, PC; Baker, AA; Griffiths, AD; Hellstrom, JC; Bajo, P; Abram, NJ; Fairchild, IJ; Borsato, A; Markowska, M; Gagan, MKSpeleothems from Golgotha Cave in SW Western Australia have been investigated to extend our knowledge of past climate variability for this region during the last millennium. O isotopic datasets, the primary paleoclimate proxy used for speleothems, were constructed for four stalagmites. A challenge in their interpretation has been the disagreement between these records, despite representing coeval growth from within the same cave. Resolving this conundrum has necessitated the characterisation of the hydrology, hydrochemistry, rainfall isotopes7 and development of proxy system forward models1,8 for Golgotha Cave. The findings of these studies will be summarised as a conceptual model in order to present the main karst hydrological features that give rise to each stalagmite’s isotopic response to hydroclimatic forcing. The paleoclimate interpretation will focus on the two continuous stalagmite records that were fed predominately by diffuse flow. This will be supported by evidence from the two stalagmites predominantly fed by fracture flow, which has resulted in a non-linear response to hydroclimatic forcing.
- ItemA post-wildfire response in cave dripwater chemistry(Copernicus Publications, 2016-07-21) Nagra, G; Treble, PC; Andersen, MS; Fairchild, IJ; Coleborn, K; Baker, AASurface disturbances above a cave have the potential to impact cave dripwater discharge, isotopic composition and solute concentrations, which may subsequently be recorded in the stalagmites forming from these dripwaters. One such disturbance is wildfire; however, the effects of wildfire on cave chemistry and hydrology remains poorly understood. Using dripwater data monitored at two sites in a shallow cave, beneath a forest, in southwest Australia, we provide one of the first cave monitoring studies conducted in a post-fire regime, which seeks to identify the effects of wildfire and post-fire vegetation dynamics on dripwater δ18O composition and solute concentrations. We compare our post-wildfire δ18O data with predicted dripwater δ18O using a forward model based on measured hydro-climatic influences alone. This helps to delineate hydro-climatic and fire-related influences on δ18O. Further we also compare our data with both data from Golgotha Cave – which is in a similar environment but was not influenced by this particular fire – as well as regional groundwater chemistry, in an attempt to determine the extent to which wildfire affects dripwater chemistry. We find in our forested shallow cave that δ18O is higher after the fire relative to modelled δ18O. We attribute this to increased evaporation due to reduced albedo and canopy cover. The solute response post-fire varied between the two drip sites: at Site 1a, which had a large tree above it that was lost in the fire, we see a response reflecting both a reduction in tree water use and a removal of nutrients (Cl, Mg, Sr, and Ca) from the surface and subsurface. Solutes such as SO4 and K maintain high concentrations, due to the abundance of above-ground ash. At Site 2a, which was covered by lower–middle storey vegetation, we see a solute response reflecting evaporative concentration of all studied ions (Cl, Ca, Mg, Sr, SO4, and K) similar to the trend in δ18O for this drip site. We open a new avenue for speleothem science in fire-prone regions, focusing on the geochemical records of speleothems as potential palaeo-fire archives. © Author(s) 2016.
- ItemRoles of forest bioproductivity, transpiration and fire in a nine-year record of cave dripwater chemistry from southwest Australia(Elsevier, 2016-07-01) Treble, PC; Fairchild, IJ; Baker, AA; Meredith, KT; Andersen, MS; Salmon, SU; Bradley, C; Wynn, PM; Hankin, SI; Wood, A; McGuire, EForest biomass has the potential to significantly impact the chemistry and volume of diffuse recharge to cave dripwater via the processes of nutrient uptake, transpiration and forest fire. Yet to-date, this role has been under-appreciated in the interpretation of speleothem trace element records from forested catchments. In this study, the impact of vegetation is examined and quantified in a long-term monitoring program from Golgotha Cave, SW Australia. The contribution of salts from rain and dry-deposition of aerosols and dissolved elements from soil mineral and bedrock dissolution to dripwater chemistry are also examined. This study is an essential pre-requisite for the future interpretation of trace element data from SW Australian stalagmite records, whose record of past environmental change will include alterations in these biogeochemical fluxes. Solute concentrations in dripwater vary spatially, supporting the existence of distinct flow paths governed by varying amounts of transpiration as well as nutrient uptake by deeply-rooted biomass. Applying principal components analysis, we identify a common pattern of variation in dripwater Cl, Mg, K, Ca, Sr and Si, interpreted as reflecting increasing transpiration, due to forest growth. Mass-balance calculations show that increasing elemental sequestration into biomass has the largest impact on SO4, providing an explanation for the overall falling dripwater SO4 concentrations through time, in contrast to the transpiration-driven rising trend dominating other ions. The long-term rise in transpiration and nutrient uptake driven by increased forest bioproductivity and its impact on our dripwater chemistry is attributed to (i) the post-fire recovery of the forest understorey after fire impacted the site in 2006 CE; (ii) and/or increased water and nutrient demand as trees in the overlying forest mature. The impact of climate-driven changes on the water balance is also examined. Finally, the implications for interpreting SW Australian speleothem trace element records are discussed. © Crown Copyright Published by Elsevier B.V.
- ItemRoles of transpiration, forest bioproductivity and fire on a long-term dripwater hydrochemistry dataset from Golgotha Cave, SW Australia(American Geophysical Union (AGU), 2015-12-15) Treble, PC; Baker, AA; Fairchild, IJ; Bradley, C; Mahmud, K; Andersen, MS; Meredith, KT; Mariethoz, GGolgotha Cave is located in a forested catchment in SW Australia where evapotranspiration losses from the vadose-zone are high and forest biomass has been disturbed by fire. The cave has been continuously monitored since 2005 and this extensive dataset has been used to quantify key processes determining dripwater hydrology and chemistry (Mahmud et al., 2015; Treble et al., 2013; 2015). In this paper we present a synthesis of these findings and derive a conceptual model to illustrate the main hydrochemical processes that will impact cave dripwater in similar environments. We applied mass-balance techniques to quantify sources (water/rock interactions and aerosol) and sinks (prior calcite precipitation and biomass uptake). Mass-balance results suggest that transpiration and elemental sequestration into biomass modifies dripwater ion concentrations. The vegetation uptake impacts dripwater Mg, K and SO4, with the largest impact on SO4, estimated to be up to 60% at some drip sites. Overall, our findings suggest that varying amounts of transpiration by deeply-rooted trees contribute significantly to spatial and temporal variability in dripwater solute concentrations. This is in addition to the partitioning of infiltrating water between characteristic flow pathways. Applying principal components analysis, we identify a common long-term rising trend in dripwater Cl, Mg, K, Ca, Sr and Si. We assess whether the long-term trends in dripwater solutes are driven by post-fire biomass recovery and/or the impacts of a drying climate in SW Australia. References Mahmud et al. (2015), Terrestrial Lidar Survey and Morphological Analysis to Identify Infiltration Properties in the Tamala Limestone, Western Australia, doi:10.1109/JSTARS.2015.2451088. Treble et al. (2013), An isotopic and modelling study of flow paths and storage in Quaternary calcarenite, doi:10.1016/J.Quascirev.2012.12.015. Treble et al. (2015), Impacts of cave air ventilation and in-cave prior calcite precipitation on Golgotha Cave dripwater chemistry, doi:10.1016/J.Quascirev.2015.06.001.
- ItemUnderstanding climate proxies in southwest-Australian speleothems(Royal Swedish Academy of Science, 2008-08) Treble, PC; Fairchild, IJ; Fischer, MJThere are two avenues for comparing speleothem-derived climate proxy data against instrumental climate measurements: Via speleothems that have grown through the 20th century, and by carrying out dripwater monitoring studies. Both provide opportunities to investigate how speleothem geochemistry responds to changes in intra- and inter-annual variations in climatic parameters. © 2008, Royal Swedish Academy of Science