Fire, Water and the Earth Below: Quantifying the Geochemical Signature of Fire in Infiltration Water and their Impacts on Underlying Karst Systems

Abstract:

Fires are natural hazards that affect communities globally and while many studies about their effects on environments such as forests and woodlands have been extensively researched, the effects of fire on karst is a topic that is not well understood. The sensitivity of caves to environmental changes make karst systems natural record keepers of environmental events and have been used as proxies for paleo environmental studies in recent times. Building on from this, karsts could potentially also be used to extend currently known fire histories beyond recorded events further back in time. Identifying quantifiable signatures in infiltration water characteristics from the burnt environments and how they are altered as they travel from a soil dominated medium (overlying soil) to a carbonate dominated medium (underlying karst system), is the key identifying fire signatures in the caves through which these waters flow.

Multiple infiltration experiments conducted using a soil column set up (soil profiles from burnt environment) amended to represent a subsurface cave system (Fig. 1), have been conducted to measure chemical composition, organic matter, carbon dioxide concentrations, pH, electronic conductivity and alkalinity after a controlled fire over the test site at Yarrangobilly Caves in the Snowy Mountains, NSW. Recurring trends in the variables of the infiltration water could be identified and used to identify a fire signature originating from surface to cave.

The fire event on which this paper is based is a cool controlled fire over Yarrangobilly Caves, very similar to back burning practises undertaken in regions prone to wildfires globally. In saying this, samples from hotspots that had experienced higher temperatures, had also been collected for this experiment to simulate the effects of hotter wildfires on the underlying karst systems.

Figure 1: Soil column with isolated chamber containing limestone used to represent a subsurface karst environment