magazine story to find out more.
oxides are used as tracers to determine which parts of a watershed are eroding,
and where erosion begins. Clockwise from top center: praseodymium, cerium,
lanthanum, neodymium, samarium, and gadolinium. Below, sediment that collects
in the sampling shed is later analyzed for rare-earth tracers.Click the
images for more information about them.
A Rare-Earth Approach to Tracking Erosion
Pons June 10, 2005
Two Agricultural Research Service (ARS) scientists believe that rare-earth
elements may be the best tool for tracking--and pinpointing sources of--costly
Zhang and agricultural engineer
Nearing of ARS like these compounds because they can be used quickly,
accurately and safely to track erosion. It was Nearing who introduced the
technology here from China.
Rare-earth elements, which are listed in their own niche of the
Periodic Table of the Elements, are actually abundant in Earth's crust. But in
soil, they're usually found only in tiny, trace amounts. According to Zhang,
the trick to using them to track erosion is to place enough tracer in the soil
so that its concentration in collected sediment is about
three times its usual concentration.
Zhang and Nearing mix them with soil and distribute them with a device
similar to a fertilizer spreader. Later, in the lab, they detect the elements
in sediment through a spectrometry procedure using a new extraction technique
that they developed.
There are 30 rare-earth elements. The scientists are working with the
following lanthanide oxides: lanthanum, cerium, praseodymium, neodymium,
samarium and gadolinium.
The researchers said the fine-powder elements are a more effective
tool for tracking movement of eroding sediment than what's currently the most
widely used tracer: minuscule amounts of the radioactive element cesium (137Cs)
that originated from nuclear-bomb testing and spread across the landscape via
atmospheric wind currents.
The scientists started this work when they were with ARS'
Soil Erosion Research Laboratory in West Lafayette, Ind. Zhang now works at
Research Laboratory in El Reno, Okla., and Nearing is with the ARS
Watershed Research Center in Tucson, Ariz.
about the research in the June 2005 issue of Agricultural Research
ARS is the U.S. Department of
Agriculture's chief in-house scientific research agency.