WASHINGTON (Reuters) - 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 U.S. 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 U.S.,” 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.”
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 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.
Editing by Julie Steenhuysen and Bill Trott