Water quality responses to fire, with particular reference to organic-rich wetlands and the Swan Coastal Plain: A review
Royal Society of Western Australia
Faculty of Computing, Health and Science
School of Natural Sciences / Centre for Ecosystem Management
The unconfined aquifers on the Swan Coastal Plain provide the population of Perth with much of its scheme water and the questionable effects of fire on the quality of surface and ground water, and recharge volumes, remain unanswered. In addition, recent concerns about fire in organic sediments and the effects of groundwater decline on acid sulphate soils have increased the need for research. Based mainly on a review of relevant literature, we formulate hypotheses as to the possible effects of fire on water quality in wetlands, particularly organic-rich ones, on the Swan Coastal Plain. Water quality responses may occur due to catchment effects (increased runoff and erosion, explainable by removal of canopy cover and changes in soil water repellency, resulting in nutrient and sediment fluxes into the wetland, elevated cation concentration and a shift to . alkalinity) and atmospheric effects (the return to the ground of dissolved volatilized reactive and particulate compounds). For both these effects, on the Swan Coastal Plain the over-riding catchment influences are the ways in which the wetlands interact with the shallow unconfined aquifers and how a fire and a changed fire regime might affect this relationship. Profound changes to water quality are possible upon rehydration of burnt or overheated (organic) soils. Cracking and erosion caused by fire can expose acid sulphate soils to oxidizing conditions, resulting in lower pH and mobilization of heavy metals. Superimposed on all these changes are the trophic consequences and how they might influence water quality. Finally we discuss the secondary effects that arise from management attempts to control or prevent fire in a wetland, such as fire suppression effects, flooding or trenching to stop a peat burn, or prescription burning around a wetland to reduce fuel loadings, each of which might trigger or exacerbate any of the above mentioned water quality responses. Management should therefore apply a precautionary approach to prevent irreversible losses (like erosion of organic soil profiles) and otherwise use an adaptive management approach to test the hypotheses stated herein.