Browsing by Author "Baker, AC"

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    Cave radon exposure, dose, dynamics and mitigation
    (National Speleological Society, 2021-03) Waring, CL; Hankin, SI; Solomon, SB; Long, S; Yule, A; Blackley, R; Werczynski, S; Baker, AC
    Many caves around the world have very high concentrations of naturally occurring 222Rn that may vary dramatically with seasonal and diurnal patterns. For most caves with a variable seasonal or diurnal pattern, 222Rn concentration is driven by bi-directional convective ventilation, which responds to external temperature contrast with cave temperature. Cavers and cave workers exposed to high 222Rn have an increased risk of contracting lung cancer. The International Commission on Radiological Protection (ICRP) has re-evaluated its estimates of lung cancer risk from inhalation of radon progeny (ICRP 115) and for cave workers the risk may now (ICRP 137) be 4–6 times higher than previously recognized. Cave Guides working underground in caves with annual average 222Rn activity > 1,000 Bq m⁻3 and default ICRP assumptions (2,000 workplace hours per year, equilibrium factor F ₌ 0.4, dose conversion factor DCF ₌ 14 µSv (kBq h m⁻3)⁻1 could now receive a dose of > 20 mSv y₋1 . Using multiple gas tracers (δ13C-CO2, Rn and N2O), linked weather, source gas flux chambers, and convective air flow measurements a previous study unequivocally identified the external soil above Chifley Cave as the source of cave 222Rn. If the source of 222Rn is external to the cave, a strategy to lower cave 222Rn by passively decreasing summer pattern convective ventilation, which draws 222Rn into caves, is possible without harming the cave environment. A small net annual average temperature difference (warmer cave air) due to geothermal heat flux produces a large net annual volumetric air flow bias (2–5:1) favoring a winter ventilation pattern that flushes Rn from caves with ambient air. Rapid anthropogenic climate change over decades may heat the average annual external temperature relative to the cave temperature that is stabilized by the thermal inertia of the large rock mass. Relative external temperature increases due to climate change (Jenolan Caves, 2008–2018, 0.17°C) reduces the winter pattern air flow bias and increases Rn concentration in caves. © The Authors
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    Hydrological 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, IJ
    The 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
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    Impact of fire on hydrological and chemical signatures in karst vadose zone water, Wombeyan Caves, New South Wales, Australia
    (National Centre for Groundwater Research And Training, 2017-07-11) Bian, F; Coleborn, K; Flemons, I; Treble, PC; Baker, AA; Baker, AC
    Impact of wildfire on karst-vadose-zone hydrology and hydrogeochemistry is hard to evaluate owing to the complexity of subsurface environment. The aim of this study is to understand the variation of hydrogeochemical components and drip discharge in response to a moderate-intensity 10m x10m experimental fire above the shallow Wildman’s Cave at Wombeyan, Australia, in May, 2016. Water isotopes and cation analyses were conducted on drip waters collected pre- and post-fire. Ongoing drip water collection began in Dec, 2014. And drip rate has been monitored continuously using acoustic data loggers. Discharge into cave is discontinuous, indicative of limited soil and karst storage. The post-fire drip data demonstrate decreased duration of recharge, with approximately x3 increase in peak discharge, which we hypothesize is caused by the decrease of soil-storage capacity. Water isotope compositions have significantly changed after fire, with d2H isotope composition up to ~56 per mil lower and d18O ~6.3 per mil lower in the week after fire. With time, isotopic values return to pre-fire values. We hypothesize that this temporary depletion in water isotopic composition reflects a combination of post-fire rainfall isotope composition, loss of pre-fire evaporatively enriched soil and shallow karst stored water.Drip water concentrations of bedrock-related elements (Calcium, Strontium) and soil-related elements (Zinc, Nickle) decreased after the fire. We hypothesize that these reflect the loss of soil and soil biological activity above the cave, and agree with a decrease of soil storage capacity. This research demonstrates that even in complex hydrogeological settings, understanding the impact of local wildfire on subsurface system can be improved through the combination of drip water hydrograph analysis and geochemical analysis. This will provide opportunities to broaden the insights into improved fire management in karst environments and a better understanding of the relationship between surface environment conditions and vadose zone hydrology.
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    The 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, S
    Fire 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.
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    The 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, S
    Wildfire 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.