Researchers discover dust plays prominent role in nutrients of mountain forest ecoystems

The study shows that dust also may be crucial in mountainous forest ecosystems, dominating nutrient budgets despite continuous replacement of depleted soils with fresh bedrock via erosion. Directly quantifying the importance of dust, which is sensitive to changes in climate and land use, is particularly crucial for predicting how ecosystems will respond to global warming and land-use intensification.

“Before this study, no one appreciated the importance of dust in mountains such as the Sierra Nevada,” says Cliff Riebe, a UW associate professor in the Department of Geology and Geophysics. “The Sierra Nevada is not unlike Wyoming's Wind River Range, a landscape where erosion is rapid, but dust still is an important factor. Dust has plant-essential nutrients, like phosphorus, in it.”

“It was only recently that we've come to understand the importance of dust in tropical ecosystems with high rainfall or chemically depleted soils,” says Sarah Aciego, a UW adjunct faculty member in geology and geophysics, as well as an adjunct assistant professor in the University of Michigan's Earth and Environmental Sciences Division. “That airborne dust also fertilizes mountainous continental landscapes with moderate rainfall is surprising, and has important implications for ecosystem evolution.” A

paper, titled “Dust Outpaces Bedrock in Nutrient Supply for Montane Forest Ecosystems,” appears in the March 28 issue of Nature Communications. Nature Communications is an open access journal that publishes high-quality research in biology, chemistry, Earth science, physics and all related areas.

Aciego is lead author of the paper, while Riebe is the second author. Ken Sims, a UW professor of geology and geophysics; as well as researchers from the University of California-Riverside and the University of California-Merced contributed to the paper.

Before the Sierra Nevada study commenced, Riebe says he was fully expecting — based on his experience in the Wind River and Snowy ranges — to learn that nutrients in bedrock were more important than nutrients in the dust.

“Bedrock is being dwarfed by the dust in terms of providing nutrients to the ecosystem,” Riebe says of the Sierra Nevada. “Although we knew this occurred in tropical landscapes, this is completely new to mountainous, semiarid climates. It's surprising.”

Our measurements indicate that the amount of the nutrient phosphorus in this dust is equal to, or larger than, the amount that comes from bedrock, the assumed source of soil nutrients,” Aciego says. “This is a game changer for our understanding of how ecosystems develop and are sustained.”

The study took place over the last two and a half years. To gather samples, Aciego, Riebe and others put out passive dust collectors at various points in the mountain range and in the nearby Central Valley.

Strontium and neodymium isotopes in modern dust show that Asian sources contribute 18 percent to 45 percent of dust deposits across the Sierra Nevada California study sites, according to the study. Riebe says the Asian dust was found to have settled in the mountains. The remaining dust originates regionally from the nearby Central Valley.

Riebe says the group also sampled the dust across time. After rains, the percentage of Asian dust found was higher. During the dry season, the percentage of Central Valley dust found was higher.

Aciego agrees, saying the study shows that California's Central Valley produces more dust than people had thought and that this dust makes it to high elevations. This finding is important because it is well known that valleys become dustier during droughts, but no one has previously shown that “valley” dust travels very far, she says.

“Once that dust gets to these mountain ecosystems, it acts just like a lawn fertilizer, causing some plants to thrive and potentially inhibiting others,” Aciego says. “We can infer that climate change — which is expected to increase the frequency of periodic, extreme droughts — will change the diversity and health of mountain ecosystems.”

Riebe concurs these findings can assist with predicting effects of climate change.

“Dust contributes a large amount of phosphorus to the soil. That's a surprise,” Riebe says. “This is a paradigm shift. It means we have to worry about this. If deserts expand, as they are predicted to do, we'll have more dust in the atmosphere. This will help us better predict effects of climate change. With more dust, we can predict more phosphorus coming in.”