In the 1930s, fierce dust storms created by drought conditions and farming
techniques that led to soil erosion swept the prairies of the western United
States, causing widespread ecological calamity.
But this so-called Dust Bowl period was just a small example of a huge increase
in dustiness in the US West in the past 150 years due to human activities such
as settlement, farming and livestock grazing, scientists said on Sunday.
The researchers drilled into lake-bed sediments in two small alpine lakes high
in the San Juan Mountains of southwestern Colorado to measure the amount of dust
deposited in the past 5,000 years. Dust blown into these lakes settles to the
bottom and accumulates as sediment.
Starting in the period from about 1860 to 1900, the dust deposit rates surged at
least fivefold over previous levels -- coinciding with a upswing in human
activities that kicked up dust into the atmosphere, scientific dating techniques
showed.
The researchers said droughts in the past 150 years were not sufficient to
explain the increase in dust levels because there had been even worse droughts
prior to that period.
"We have a lot of dust in the air in the western US," said Jason Neff of the
University of Colorado at Boulder, who led the study.
"It's a reasonable question to ask -- whether or not that dust is related to
human activity. This study pretty clearly shows that a large amount of the dust
that's in the atmosphere is related to the legacy of land use and contemporary
human uses of the landscape."
DRILLING FOR DUST
Neff's team drilled about 3 feet (1 meter) into the sediment at Porphyry Lake
and Senator Beck Lake, both situated about 13,000 feet (4,000 meters) above sea
level on a ridgeline between the towns of Telluride and Silverton, Colorado.
The study, published in the journal Nature Geoscience, is the latest to
demonstrate the dramatic impact that people are having on the environment in the
western United States.
Last month, other scientists reported that human-caused climate change has
altered river flows, snow pack and air temperatures, with a water supply crisis
looming in the western United States as a result.
Neff said other recent research showed that wind-blown dust cut the duration of
San Juan Mountains snow cover by a month, causing an earlier spring snowmelt --
with major implications for agriculture and urban water consumption.
The dust spike detected in the new study coincided with a surge in white
settlers, the building of railroads and the advent of large-scale ranching and
livestock activity. Grazing by millions of cattle on the western rangeland
caused systematic degradation of ecosystems, Neff said.
Since then, other human activities also have contributed to the dustiness,
including agriculture and the development of towns and cities, Neff said in a
telephone interview.
"The chemical composition of the dust is changing. And it's changing in a way
that we actually see the byproducts of both industrial activity and agricultural
activities in the dust. We see elevated phosphorous and we see elevated nitrogen
in these lake sediments," Neff said.
Excessive dust in the air can cause health problems including lung tissue
damage, allergic reactions and respiratory problems, Neff said.