Browsing by Author "Bian, F"

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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.