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Sci Total Environ. 2019 Apr 20;662:180-191. doi: 10.1016/j.scitotenv.2019.01.102. Epub 2019 Jan 11.

Hydrological and geochemical responses of fire in a shallow cave system.

Author information

1
Water Research Laboratory, School of Civil and Environmental Engineering, UNSW Sydney, NSW 2052, Australia; Connected Waters Initiative Research Centre, University of New South Wales, Sydney NSW 2052, Australia; School of Biological, Earth and Environmental Sciences, UNSW Sydney, NSW 2052, Australia. Electronic address: f.bian@unsw.edu.au.
2
Connected Waters Initiative Research Centre, University of New South Wales, Sydney NSW 2052, Australia; School of Biological, Earth and Environmental Sciences, UNSW Sydney, NSW 2052, Australia.
3
Connected Waters Initiative Research Centre, University of New South Wales, Sydney NSW 2052, Australia; ANSTO, Lucas Heights, NSW 2234, Australia.
4
ANSTO, Lucas Heights, NSW 2234, Australia.
5
National Parks and Wildlife Service, Bathurst, NSW 2795, Australia.
6
Water Research Laboratory, School of Civil and Environmental Engineering, UNSW Sydney, NSW 2052, Australia; Connected Waters Initiative Research Centre, University of New South Wales, Sydney NSW 2052, Australia.
7
NSW Office of Environment & Heritage, Hurstville, NSW, Australia.
8
Connected Waters Initiative Research Centre, University of New South Wales, Sydney NSW 2052, Australia; Key Laboratory of Cenozoic Geology Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China.
9
Geography, Geology and the Environment, Keele University, UK.
10
School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK.

Abstract

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.

KEYWORDS:

Fire; Groundwater; Hydrograph analysis; Karst

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