Dating drought

Wedin said during the most recent mega-drought 800 years ago, “you would have been standing at this point and looking at the largest set of moving sand dunes in the western hemisphere.”UNL scientists have spent the last 15 years dating the Sandhills through a process called optically-stimulated luminescence, which measures the energy held in sand grains.UNL Professor Paul Hanson, a geologist with the Nebraska Geological Survey, uses this technique to study how and when the sand dunes last moved.Then they load the individual grains of sand onto disks into a machine that reads the luminescence—like what you see from fireflies.“So if your eyes were more sensitive and could actually see smaller quantities of light, you could actually see the sand grains give off the light under the right conditions,” Hanson said.But since our eyes aren’t that sensitive, this machine runs 24/7, dating sand one individual grain at a time.Though surprised by the resilience of the grasslands, after the fourth and fifth winters, some of the patches did start to move, "and then it just went exponential on us.We went from an inch or two and before you knew it we were losing four to five inches on average, per month," Wedin said.And the brutal lesson was: we weren’t going to restore this vegetation in a couple years," Wedin said.

“The sand grains are exposed to sunlight, they lose their electrical charge.Hanson and his colleagues drill down 60-80 feet to take core samples of the dunes, then return to their lab to study them.On the UNL campus, Hanson leads the way through a rotating door of darkness to enter the lab lit by red and amber lights.Even with surface vegetation killed, the stressed grasslands proved far more resilient than Wedin imagined, retaining their root systems, sand and organic matter for years.He’s now trying to revegetate the plots, which he said has been even harder:“It’s a situation where the professors come out and learn something that everybody that lives out here already knew: that it’s easier to destroy the stability out here in the Sandhills than it is to restore it once it’s lost,” Wedin said.

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