by Timothy Oleson Monday, January 5, 2015
The U.S. Geological Survey (USGS) recently completed a seven-year soil-mapping project detailing the mineralogy and geochemistry of soils across the lower 48 U.S. states. Bill Cannon, an emeritus scientist at the USGS in Reston, Va., and co-author of the report, which was published in 2014, discussed the effort last October at the Geological Society of America’s annual meeting in Vancouver, B.C.
Sampling was conducted at 4,857 sites — one per 1,600 square kilometers — and at each site, soil samples were collected at three depths: from the surface layer down to 5 centimeters depth, from the “A horizon” or topsoil beneath the surface layer, and from the “C horizon,” which consists largely of bedrock regolith. Samples were then tested for their mineralogy and for 45 major and trace elements. The new data provide “an estimate of the abundance and spatial distribution of chemical elements and minerals in soils of the conterminous United States and represent a baseline for soil geochemistry and mineralogy against which future changes may be recognized and quantified,” according to the report’s abstract.
Along with the report, which presents the results in detail, USGS has created an interactive website where visitors can view data of interest — the abundance of lead in the surface soil layer, for example — overlaid on a U.S. map. Statistics for each dataset are available for display, and users can export data to Google Earth and create PDFs or images of customized maps.
Paraphrasing the science writer Deborah Blum, the report authors wrote: “The data aren’t so fine that they will tell you what lies in your backyard behind the raspberry bush; however, they will show you the metal and mineral patterns that color your part of the world and they will remind you — as they should — of the astonishing and diverse chemistry that the planet creates under our feet.”
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