Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0900758106 (2009)

Dust deposited on mountain snow increases the amount of solar radiation absorbed, causing it to melt about a month earlier than clean white snow. Many ecologists have suspected that this leads to much earlier growth in previously snow-covered vegetation.

A team led by Heidi Steltzer at Colorado State University in Fort Collins set up 13 experimental plots in Colorado's San Juan Mountains, adding dust to some, scraping others clean, and covering some in dark fabric to control the timing of the thaw.

Contrary to expectation, the team found that after an early thaw — when temperatures were still freezing — vegetation didn't grow for more than two weeks. This delay, Steltzer says, might mean that nitrogen released in the melt could go to waste and may contribute to the elevated nitrogen levels seen in some alpine lakes.