Fire Effects on Water Quality

Fire can have either positive or negative effects on the physical, chemical, and biological structure of aquatic systems. The effects of fire on water quality are dependent upon the fire size, intensity, and severity. Fire effects also depend on the proximity of fires to streams and other water sources as well as the timing of fires in relation to precipitation events. The effects of fire on aquatic ecosystems can be divided into direct and indirect effects. Direct effects may include increases in temperature, ash, nutrients, and charcoal. The indirect effects of fire may include increases in sediment deposition and turbidity, and alterations channel morphology.

In general, studies in the Southeast have shown that fires do not produce significant changes in water quality (Table: Fire effects on water quality in the southeast). In most of these studies, only short-term nutrient and/or sediment increases were observed. These effects were generally attributed to wildfire or the subsequent watershed restoration efforts. Fires in the Southeast also showed minimal effects on hydrological parameters. Only intense fires impose the risk of increased hydrophobicity (i.e., water repellency) on soils, which could result in increased overland flow. In general, these studies suggest that properly executed prescribed burns can actually protect water quality by reducing the risk of severe wildfires. It is important for managers to follow guidelines that minimize the effects of fire on soil and water quality, and take special precautions when burning in areas critical to water quality such as riparian zones and wetlands.

The following sections summarize current research on the effects of fire on indicators of water quality:

• Fire Effects on Stream Nutrients
• Fire Effects on Stream Sediment
• Fire Effects on Watershed Hydrology
• Thermal Effects of Fire on Streams