This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Wildfire smoke is usually discussed as an airborne pollutant and a threat to human health. But when smoke and rain coincide, nutrients released by burned landscapes rain back down.
A new study finds that smoke-rain events can deliver large bursts of nitrogen, phosphorus and potassium—three nutrients essential to life—across ecosystems in the United States. As wildfires become more frequent, these nutrient pulses could become an increasingly important and largely overlooked ecological consequence of fire. "It's important to remember that what goes up must come down," said lead author Alexandra Ponette-González, urban ecologist at the University of Utah (U) and Natural History Museum of Utah.
"There's so much focus on what goes up and how that affects human health. We're interested in everything that falls out of the atmosphere and lands on ecosystems, and what that means for our environment." Led by researchers at the U, Utah State University (USU) and the Cary Institute of Ecosystem Studies (Cary Institute), the study is the first large-scale analysis to examine how particles in wildfire smoke are delivered to ecosystems through rainfall across hundreds of U.S. sites over multiple years. The work is published in the journal Global Change Biology.
Using satellite-derived smoke observations and national network rainfall data, the researchers quantified how often smoke and rain coincided and how much of several nutrients were deposited during those events. Their analysis covered 250 sites across 16 climate regions in 2014, 2020 and 2022. The results showed many more smoke-rain days in 2022 than in 2014, while regional hotspots shifted from year to year.
Although the events were relatively infrequent, they delivered a disproportionately large share of nitrogen, phosphorus and potassium to the study sites. "Nutrient delivery from air to ecosystems as a result of fossil fuel burning or agriculture can be significant, but the impact of wildfire on rain chemistry has been largely overlooked," noted co-author Kathleen Weathers, ecosystem scientist at the Cary Institute. As wildfires burn through landscapes, they consume vegetation and other materials, sending a mix of particles and gases into the atmosphere.
Some of that material ends up in rain. When rain falls through the smoke, it washes the particles to the ground in a process known as wet deposition. Once dissolved in water, nutrients from the smoke become immediately available to plants and other organisms.
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