Fire suppression and burnt sediments: effects on the water chemistry of fire-affected wetlands

Preventing fire from entering wetland areas during seasonal or prolonged drought, or suppressing fire once it has entered a wetland, requires consideration of the consequences of the fire-management action on water quality. Two approaches can be taken to suppress such fires: chemical fire retardants or the flooding of sediments. We determine a lack of information relating to the effects of these approaches for water quality within fire-affected wetlands. The aim of this study was to gain a preliminary understanding of the effects of three treatments: two chemical treatments and saturation. Microcosms were established to test sediments from a wetland on the Swan Coastal Plain, Western Australia, which were exposed to temperatures ranging from 30 to 800°C. The results indicate that one of the fire-retardant chemicals increased the soluble nutrient load present in the water column, as predicted by the results of other research. However, the same chemical had a minor but important effect as an acidity buffer when the organic, pyritic sediment was heated but not burnt. The second chemical treatment did not increase the nutrient load but neither did it buffer the acidity generated by the heating and burning of the organic sediment. It was virtually indistinguishable from the saturation treatment in this regard.