Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
Hydrol. Earth Syst. Sci., 20, 2745-2758, 2016
https://doi.org/10.5194/hess-20-2745-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
21 Jul 2016
A post-wildfire response in cave dripwater chemistry
Gurinder Nagra1, Pauline C. Treble1,2, Martin S. Andersen1, Ian J. Fairchild3, Katie Coleborn1, and Andy Baker1 1Connected Waters Initiative Research Centre, University of New South Wales, Sydney, NSW, 2052, Australia
2Institute for Environmental Research, Australian Nuclear Science and Technological Organisation, Lucas Heights, NSW, 2234, Australia
3School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, UK
Abstract. Surface 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.

Citation: Nagra, G., Treble, P. C., Andersen, M. S., Fairchild, I. J., Coleborn, K., and Baker, A.: A post-wildfire response in cave dripwater chemistry, Hydrol. Earth Syst. Sci., 20, 2745-2758, https://doi.org/10.5194/hess-20-2745-2016, 2016.
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Short summary
Our current understanding of wildfires on Earth is filled with knowledge gaps. One reason for this is our poor record of fire in natural archives. We open the possibility for speleothems to be "a missing piece to the fire-puzzle". We find by effecting surface evaporation and transpiration rates, wildfires can have a multi-year impact on speleothem, forming dripwater hydrology and chemistry. We open a new avenue for speleothems as potential palaeo-fire archives.
Our current understanding of wildfires on Earth is filled with knowledge gaps. One reason for...
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