June 30, 2009

Desert Dust Causing Premature Mountain Snowmelt

According to a new study, dust blown in from deserts may be disrupting the annual life-cycle of plants in the alpine regions surrounding mountains chains.

In the report published in this week's edition of the Proceedings of the National Academy of Sciences, scientists described how desert dust blowing from an increasing number of dry regions may be changing the rate at which snow melts from mountain tops and thus affecting the rate and timing with which it is distributed to surrounding ecosystems.

Traditionally, mountain snow first began to melt in coordination with the gradually warming temperatures of spring, delivering water to surrounding areas just as green plants were beginning to blossom and reproduce.

Authors of the report say that now, however, dust blowing in from expanding deserts is increasingly being deposited on mountain surfaces, causing a darkening of the winter snow. 

As the darkly-colored snow absorbs significantly more of the sun's warming rays than reflective white snow, it begins to melt much earlier than in the past, streaming down into the surrounding areas before warming spring temperatures have arrived.

Scientists say that snowmelt is one of several natural cues that plants use to time their growth and reproductive cycles. The potential effects of the altered timing on alpine plants have some researchers concerned about the future of these already delicate ecosystems.

"Desert dust is synchronizing plant growth and flowering across the alpine zone," said the project's leader Heidi Steltzer of Colorado State University. "Synchronized growth was unexpected, and may have adverse effects on plants, water quality and wildlife."

"Climate warming could therefore have a great effect on the timing of growth and flowering," she added.

Experts say that the quantity of dust observed in mountain snow today is roughly five-fold higher than it was some 150 years ago prior to the industrial revolution.  Some researchers believe this to be no coincidence

"Human use of desert landscapes is linked to the life cycles of mountain plants, and changes the environmental cues that determine when alpine meadows will be in bloom, possibly increasing plants' sensitivity to global warming," said Jay Fein, program director in the National Science Foundation (NSF)'s Division of Atmospheric Sciences, which helped to sponsor the research project.

In an alpine basin in the San Juan Mountains, the researchers experimentally studied the effects of dust on snowmelt by setting up artificially dusted and non-dusted regions of snow. They then measured degree to which dust accelerated the melting process.

"It is striking how different the landscape looks as result of this desert-mountain interaction," said co-author of the study Chris Landry, director of the Center for Snow and Avalanche Studies in Silverton, Colo.

But the potential consequences of early snow melt could be much more than just aesthetic in nature.  Researchers say that it could eventually lead to a scarcity of resources for a number of animal and plant populations, leaving marginally competitive species little chance for survival.

Steltzer fears that the coordination of blossoming and growth period for plants could cause a short yearly abundance of resources in the spring and early summer with an intense scarcity in the later months.

"With increasing dust deposition from drying and warming in the deserts, the composition of alpine meadows could change as some species increase in abundance, while others are lost, possibly forever," explained Steltzer.


Image Caption: More dust covers snow in the San Juan Mountains of Colorado than previously documented. Credit: Center for Snow and Avalanche Studies


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