Wildfire on Karst: an Overview

Abstract:

Wildfires dramatically change the surface environment by removing vegetation and soil microbial communities and altering soil structure and geochemistry. Karst subsurface processes such as dissolution, cave formation and speleothem deposition are sensitive to environmental change, which is precisely why speleothems have been widely used as recorders of surface and climate change at an annual to millennial temporal scale. The effect of fire on karst processes is poorly understood. We hypothesise that a wildfire induced change at the surface will impact karst dissolution and precipitation processes. Firstly, sterilisation of the soil by heating causes a reduction in soil CO₂ concentration which is a key component in dissolution processes. Secondly, removal of vegetation alters surface albedo and soil water storage properties. This could change the hydrology and isotopic signature of speleothem-forming drip water. We also hypothesise that a wildfire will produce a unique biogeochemical signature due to a change in the organic and inorganic properties of soil, which can be transported into speleothem forming drip water. Fire changes the organic matter character which is an important component in the mobilisation and transport of trace metals. Combustion of vegetation results in addition of ash derived minerals to the soil. Quantifying the biogeochemical signature from a burnt landscape will enable us to determine whether this wildfire signature is preserved in speleothems. This would provide the opportunity to use speleothems as recorders of fire history for the first time. Determining the impact of fire on karst processes would inform fire management and karst conservation policies.