Browsing by Author "Roshan, H"

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    Dripwater 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, G
    A 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.
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    Evaporative cooling of speleothem drip water
    (Nature Publishing Group, 2014-06-04) Cuthbert, MO; Rau, GC; Andersen, MS; Roshan, H; Rutlidge, H; Marjo, CE; Markowska, M; Jex, CN; Graham, PW; Mariethoz, G; Acworth, RI; Baker, AA
    This study describes the first use of concurrent high-precision temperature and drip rate monitoring to explore what controls the temperature of speleothem forming drip water. Two contrasting sites, one with fast transient and one with slow constant dripping, in a temperate semi-arid location (Wellington, NSW, Australia), exhibit drip water temperatures which deviate significantly from the cave air temperature. We confirm the hypothesis that evaporative cooling is the dominant, but so far unattributed, control causing significant disequilibrium between drip water and host rock/air temperatures. The amount of cooling is dependent on the drip rate, relative humidity and ventilation. Our results have implications for the interpretation of temperature-sensitive, speleothem climate proxies such as delta O-18, cave microecology and the use of heat as a tracer in karst. Understanding the processes controlling the temperature of speleothem-forming cave drip waters is vital for assessing the reliability of such deposits as archives of climate change. © 2014, Nature Publishing Group.
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    A groundwater recharge experiment in krast - Wellington Caves, NSW
    (International Association of Hydrogeologists, 2013-09-16) Andersen, MS; Baker, AA; Graham, PW; Rutlidge, H; Mariethoz, G; Roshan, H; Rau, GC; Markowska, M; Cuthbert, MO
    Groundwater recharge is a process which is inherently difficult to measure directly due to soil and sediment heterogeneity and the tendency for this to cause preferential flow. This often leads to groundwater recharge being estimated by indirect methods, such as remotely or by differences in the water balance, which frequently causes huge uncertainties in the estimates. Karst terrains with cave features, although notoriously heterogeneous, offer a rare opportunity to physically enter the subsurface and make direct observations. Cathedral Cave at Wellington Caves in NSW, Australia was used for a multiple tracer experiment to look a recharge processes as well as physical and chemical processes affecting speleothems formation. On four consecutive days, four water releases were applied to a 3 x 7 m soil patch 2-3 m above the cave ceiling. The applications varying from 800 to 1500 L corresponds to natural precipitation events of 40 to 70 mm, events which have been known to cause recharge into the caves in the past. The four different events were variably modified by adding deuterium (2H), a fluorescing tracer and ice to reduce the temperature. Inside the caves onset of recharge was measured by automatic drip rate monitoring and temperature loggers. In addition, discrete water samples were collected and analysed for stable water isotope composition, fluorescence and dissolved trace elements. A preliminary assessment of the cave observations suggest that. although ow was preferentially along fractures, considerable interaction with pore water in the rock matrix must have taken place to significantly dilute the tracer content of water sampled in the cave. To our knowledge this is the first time that is has been directly shown that water sampled during a recharge event is only fractionally water from that particular event. For the location of this study the result is surprising considering the short distance of 2-3 m between the soil surface and the cave ceiling. The results have significant implications for our understanding of karst hydrology as well as reconstruction of past recharge and climate conditions from cave speleothems.
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    Tracking the diffusion of hydrogen rich liquids in shale rocks
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Siddiqui, M; Salvemini, F; Roshan, H
    Understanding flow of hydrogen rich liquids in shale rocks is critical for the recovery of unconventional hydrocarbon resources. The most common hydrogen rich liquids pertaining to shale rocks are water and oil. The extensive research on water and oil flow in shale rocks has not yet been able to explain the significant uncertainties and discrepancies in reported experimental data. Specifically, what has perplexed the research community is that despite oil spreading more than water on shale surfaces in an inviscid medium, its uptake by shale pores under pure capillary forces is much less than water contrary to theoretical expectations. This causes misjudgement of shale wettability and the underlying physical phenomena. Therefore, in this study, we have used neutron computed tomography (CT) in combination with other experimental and digital rock methods to investigate water and oil flow in an organic-rich shale from the Beetaloo sub-basin in Northern Territory, Australia. The experimental techniques included, in addition to neutron CT, contact angle and spontaneous imbibition tests, X-ray CT, and small angle X-ray scattering. We also used non-equilibrium thermodynamics to theoretically derive constitutive equations to support our experimental observations of configurational diffusion. The results of this study indicated that the pre-existing fractures imbibe more oil than water consistent with theory. However, theoretically in contrast, the overall imbibition was higher for water than oil. The reason for this was revealed by neutron CT to be greater water diffusion into the shale matrix (second continuum) from the fractures. It was shown that more water uptake into shale was controlled by pore size and accessibility in addition to capillary or osmotic forces i.e. the diffusion type is configurational where water molecules have easier access to smaller pores due to their smaller molecular size compared to larger oil molecules. Thus, even the inorganic pores which seem more oil-wet in an inviscid medium, easily allow water molecules to pass through them compared to oil. On the other hand, strongly oil-wet pores possessing strong capillarity cannot even imbibe oil simply due to its large molecular size and physical inaccessibility to the micro-pores. A combination of neutron and x-ray CT methods revealed that different flow mechanisms are dominant in different continua of shale rocks - and that these mechanisms are dependent on the relative sizes of liquid molecules and pores. The results provide new insights into the previously unexplained discrepancy regarding water and oil uptake capacity of shale rocks.
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    What controls the cave drip water temperature? Analysis and implications for paleoclimate reconstruction from speleothems
    (National Centre for Groundwater Research And Training, 2015-11-03) Rau, GC; Cuthbert, MO; Andersen, MS; Baker, AA; Rutlidge, H; Markowska, M; Roshan, H; Marjo, CE; Graham, PW; Ackworth, RI
    Cave drip water temperature influences cave hydrobiochemical processes and also speleothem based paleoclimate signals (e.g. biomarkers, isotopes, etc). Yet very little is known about what controls cave drip water temperature. This experimental investigation reveals the dominant heat transfer mechanisms. Design and Methodology: A shallow cave drip water flow path along a flowstone was instrumented with a number of high resolution temperature sensors and drip loggers. Cave and surface climate parameters: Pressure, Relative Humidity (RH) and Temperature were monitored with high frequency. Three separate land surface irrigation experiments were conducted comprising of multiple applications of water at the surface above the cave. One of the irrigation batched was enriched with deuterium (610% VSMOW) as a conservative tracer. The cave drip water temperature measurements clearly reveal the presence of all common heat transport mechanisms (e.g. conduction, convection, latent heat exchange). In general, the cave drip water has the same temperature as the subsurface conduction profile of the rock at that depth. However, at fast flow rates the warmer/colder signal during summer/winter is being washed down convectively leading to temperature anomalies of up 1.5 °C. Importantly, daily cave venting reduces the cave RH thus leading to evaporative cooling of drip water of up -2.5 °C. Cave drip water temperature is mainly controlled by the subsurface heat conduction profile as well as the cave climate. This, however, depends on the drip rate and length of flow path exposed to the cave air. Paleoclimate reconstruction requires depth-dependent deconvolution of the subsurface conduction signal as well as consideration of past or present cave venting and evaporative cooling.
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    Where is the water going: an irrigation experiment using a natural isotopic tracer in karst SE, Australia
    (European Geosciences Union, 2014-05) Markowska, M; Baker, AA; Andersen, MS; Cuthbert, MO; Rau, GC; Jex, CN; Rutlidge, H; Marjo, CE; Roshan, H; Treble, PC
    The karst unsaturated zone is a fractured rock environment associated with very heterogeneous water movement; spatial variability in the subsurface water storage; and fast preferential flow through fractures and fissures. These factors dominate the way in which water moves within the unsaturated zone in these environments, giving rise to flow path complexities less common in homogenous media. Currently there is limited research regarding karst infiltration/storage processes and potential evaporation in the unsaturated zone. Such processes may have the potential to alter the stable isotopic composition of groundwater. Caves provide a unique environment within which to examine exfiltration variability and flow dynamics in situ. In semi-arid environments evaporative processes in the unsaturated zone have been shown to directly alter the isotopic δ18O composition of cave drip waters, fractionating them towards heavier ratios, by a magnitude of 1-3 per mil relative to mean annual rainfall (Bar Matthews et al., 1996; Cuthbert et al., 2014). Here we present a novel isotopic drip water study from an artificial infiltration experiment at Wellington Caves, SE Australia. A series of four artificial infiltration events were initiated directly over Cathedral Cave, Wellington over as many days. The first event was spiked with a deuterium tracer and the subsurface response was monitored during several sampling campaigns over the following year. The infiltration study revealed: (1) isotopic break-through curves suggest a front of older water from the unsaturated zone storage arrived ahead of the infiltration water, (2) water residence times in the unsaturated zone were found to be longer than 6 months and, (3) large spatial heterogeneities existed in the proportion of exfiltrated deuterium tracer at different drip sites in the cave suggesting unique pathways and sources of water in the unsaturated zone. Implications from this study include the interpretation of paleo-climate speleothem records from semi-arid to arid environments. © Author(s) 2014.