CWRU GEOLOGISTS DEVELOP FIRST MEANS TO MEASUER AMOUNT, TYPE OF SOIL EROSION
16 January 2002 - Case Western Reserve University

When it rains, it does more than pour. It washes away soil. In the past, farmers could only estimate their soil loss. Now, for the first time, three CWRU geologists have found "the recipe" to determine the amount and style of soil erosion.

Peter Whiting, CWRU associate professor of geological sciences; E. Chris Bonniwell, a CWRU alumnus from geological sciences; and Gerald Matisoff, chair and professor of geological sciences; describe this new method of measuring soil loss in the article, "Depth and areal extent of sheet and rill erosion based on radionuclides in soils and suspended sediment." The journal Geology published the article in a recent issue.

Soil erodes through rills, large or small gully-like channels, or through sheetwash, a thinly eroded surface across part or the entire field, according to Whiting. Rills are observable evidence of soil erosion and can be measured, but sheetwash is so thin that it has been difficult to quantify.

After a half inch of rain fell on 15 acres of U.S. Department of Agriculture land near Treynor, Iowa, the geologists measured three radionuclides-atoms that emit radiation and decay over time-in sediment carried off the field in order to determine the proportion of erosion produced by rills and the portion by sheetwash. Whiting likened the approach to figuring out the secret recipe for "grandma's snack mix" of pretzels, nuts and cereal.

The researchers used:
Beryllium–7, which finds its way from the atmosphere only into the top inch of soil and decays within a year;
Cesium–137, which came from nuclear bomb testing from 1950-70, and is concentrated several inches below the soil surface; and
Lead–210 from the atmosphere or from the breakdown of radon is found to depths of one foot and greater.
The geologists discovered rill erosion produced 29 times more sediment than sheet erosion. They also found that rills eroded to a depth of 1.5 inches, while sheetwash removed soil to a depth of 1/ 2000 of an inch during runoff.

Sheetwash erosion only occurred on 37 percent of the field, Whiting said, while the rills occurred on 0.4 percent. No erosion occurred on about two-thirds of the field (10 acres).

http://www.case.edu

More News:
  • For January 2002
  • From Case Western Reserve University
  • For University