If you were standing On the banks of Colorado’s Cache la Poudre River after the 2020 Cameron Peak Fire, the bubbling water might have appeared black. The mush of ash and charred soil cascaded toward reservoirs that provide drinking water to the downstream city of Fort Collins, home to about 170,000 people. Although the water appeared clear again weeks later, Charles Rhoades, a research biogeochemist at the U.S. Forest Service’s Rocky Mountain Research Station, says he still sees contamination from the fire in the watershed.
Recent studies have shown that although some catchments start regaining strength Within five years of a fire, others can change dramatically, never fully returning to pre-fire conditions. And as fires become more common, larger, and last longer as the world warms, hydrologists, ecologists, and water management officials are scrambling to understand and mitigate the effects that fire-polluted water can have on people and ecosystems.
A hearty forest has a lot of “trash” on the ground—pine needles, dead leaves, debris. “It acts like a sponge,” Rhoades says. “When rain comes, it slowly moves through that layer and can soak into the soil.” When fire scorches the earth, it burns vegetation and organic matter, leaving a bare landscape that is highly susceptible to erosion. Instead of soaking into the ground, rain runs off the surface, moving quickly, lifting soil and carrying it into streams and rivers. Not only does this cause sediment to build up, it can also disrupt water chemistry. Rhoades found increased levels of nutrientslike nitrogen, in rivers nearly 15 years after a major fire. These nutrients can lead to harmful algal blooms, although they have no direct impact on drinking water quality. But other places show increased levels of weighty metals like manganese, iron and even lead after a major fire, which can complicate water treatment processes.
Other regions in the western US, such as Taos, New MexicoAND Santa Cruz, Californiahave faced similar problems as wildfires become more regular and last longer due to climate change and decades of fire suppression practices. For most of the 20th century, the U.S. Forest Service and other land management agencies tried to stop all fires, believing that this was the best way to protect forests. However, naturally occurring, low-intensity fires improve forest health by preventing the buildup of dense brush and dead trees that act as fuel.
“We have a huge fuel buildup on the landscape from 140 years of fire suppression, and we know that the consequences of that—combined with an increase in extreme weather—make the likelihood of really intense fire behavior much higher than it used to be,” says Alissa Cordner, an environmental sociologist and professor at Whitman College in Washington state and a volunteer fire department member. “More and more people are living near forests and migrating to the wildland-urban interface.” Every community is at risk of water contamination if a wildfire burns through its watershed.
“Consumers rarely know all that’s going on under the hood,” Rhoades says. After a wildfire, water suppliers work tirelessly to keep residents from experiencing the effects in their taps, which requires cooperation between land agencies like the Forest Service, USGS and local governments. They conduct regular water tests, install sediment control structures and sometimes change treatment protocols to cope with the increased contaminant load.