Summary
USDA Forest Service scientists at the agency's Rocky Mountain Research Station evaluated whether severe wildfires such as the 2002 Hayman Fire in Colorado have any longer lasting effects on watersheds or water quality. The Hayman Fire, the largest in recorded Colorado history, burned watersheds with streams that flow into the South Platte River, affecting the drinking water supply for residents of the Denver metropolitan area as well as agricultural and industrial users. Fortuitously, the scientists and agency managers began to analyze stream water quality in tributaries of the South Platte River prior to the fire, so they were able to evaluate the short-term effect of the fire on nutrient, sediment and stream temperature; and, more recently, to track the fire’s long-term effects. Almost 15 years after the Hayman Fire, watersheds with extensive high-severity wildfire still had elevated levels of streamwater nitrogen; elevated stream carbon was found in watersheds with more moderate-severity burn area. The persistent, elevated nitrogen and carbon in burned watersheds are not a threat to drinking water quality, but they exceed expected levels for healthy reference streams in this region. The extensively burned watersheds no longer act as strong nitrogen “sinks” that retain more than 90 percent of atmospheric nitrogen inputs, as they did prior to the fire. Future recovery remains uncertain. Post-fire forest recovery has been extremely slow and may require another several decades or longer.
