Humans Erode Soil 100 Times Faster Than Nature

It turns out that when it comes to soil erosions, humans come out on top over nature. Scientists have discovered that removing native forest and starting intensive agriculture can accelerate soil erosion so dramatically that in a few decades, as much soil lost as would naturally occur over thousands of years.

A hundred years ago before European settlers began clearing land and farming in the 1700s, you would have seen that America's landscape was quite different. Yet accurately measuring the natural rate of erosion for a landscape, and therefore how much human land use has accelerated this rate, has been a difficult task for geologists.

Now, scientists have used new research on three rivers-the Roanoke, Savanna and Chattahoochee-in addition to seven other large river basins in the U.S. Southeast to better quantify the background rate of erosion. The researchers found that the hillslope erosion before European settlement was about an inch every 2,500 years; during the period of peak land disturbance in the late 1800s and early 1900s, though, rates spiked to an inch every 25 years.

"That's more than a hundred-fold increase," said Paul Bierman, one of the researchers, in a news release. "Soils fall apart when we remove vegetation, and then the land erodes quickly."

The researchers collected river samples and then examined quartz in the sediment. From this quartz, they extracted beryllium, examining how much had accumulated. The slower the rate of erosion, the longer the soil is exposed at the surface and the more beryllium builds up.

"There's a huge human thumbprint on the landscape, which makes it hard to see what nature would do on its own," said Bierman. "But the beauty of beryllium-10 is that it allows us to see through the human fingerprint to see what's underneath it, what came before. This study helps us understand how nature runs the planet compared to how we run the planet."

The findings are published in the journal Geology.

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