Central Mineral and Environmental Resources Science Center
Project status is complete. Please check the CMERSC project list for currently active projects.
The U.S. Geological Survey, Geological Survey of Canada, Agriculture and Agri-Food Canada, Servicio Geológico Mexicano, and Instituto Nacional de Estadística Geografía e Informática have collaborated on a trinational project called Geochemical Landscapes that has as its long-term goal a soil geochemical survey of North America. Our understanding of the variability in chemical composition of the soils on the North American continent is very limited. Neither Canada nor Mexico has a national-scale soil geochemical database, and the most-often-quoted data set for estimating background concentrations of metals in soils of the conterminous United States (Shacklette and Boerngen, 1984; Gustavasson and others, 2001) contains only 1,323 samples (1 sample per 2,300 square miles). As a result, our ability to recognize and quantify changes to soil composition caused by urbanization, industrialization, agriculture, mining, waste disposal, and other human activities is severely impaired. USGS Fact Sheet 015-03 explains in more detail the rationale for such a survey in the United States.
Preliminary recommendations for sample design of the continental-scale survey, sample collection protocols, and analytical methods were developed at the 2003 Soil Geochemistry Workshop. The preliminary sample design consists of a uniform grid of approximately 10,000 sites across the continent. At each site, up to five samples would be collected: 1) the upper five cm; 2) O horizon (if present); 3) a composite of the uppermost mineral soil horizon, or A horizon; 4) the most representative B horizon; and 5) C horizon. The analytical protocol includes an extensive array of major and trace elements using inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS) following a four-acid extraction to determine the near-total elemental content of the samples. This would be supplemented by single-element determinations for Hg and Se as well as analysis for total carbon, carbonate carbon, and total sulfur. Recommendations from the workshop also included 1) an estimate of bioaccessibility by a distilled-deionized water extraction and a simulated human gastric fluid extraction followed by ICP-MS; 2) analysis of a limited number of organic compounds to study long-range transport of organic pollutants and the distribution of pesticides, PAHs and their breakdown products; and 3) characterization of the microbial community in the A-horizon samples by a combination of phospholipid fatty acid analysis, enzyme assays, BIOLOG community profiling, and agricultural and human pathogen screening.
In 2004, the project entered a pilot phase to test and refine these protocols. The pilot studies were carried out at both a continental scale and a regional scale. Final protocols for the soil geochemical survey of North America were developed.
Marty Goldhaber and Dave Smith (co-chiefs of the Geochemical Landscapes Project) and W.A. (Bud) Norvell of the U.S. Department of Agriculture's Plant, Soil, and Nutrition Laboratory in Ithaca, NY convenined a symposium titled "Soil Geochemical Patterns at Regional, National, and International Scales" at the 18th World Congress of Soil Science (WCSS) (http://www.colostate.edu/programs/IUSS/18wcss/). The WCSS was held July 9-15, 2006 in Philadelphia, PA. The oral portion of the symposium consisted of three 35-minutes presentations:
| David B. Smith Phone: 303-236-1849 Email: dsmith@usgs.gov |
Martin Goldhaber Phone: 303-236-1521 Email: mgold@usgs.gov |
Download if needed: Excel Viewer | PDF Reader | Powerpoint Viewer | Word Viewer
U.S. Department of the Interior |
U.S. Geological Survey
URL: http://minerals.cr.usgs.gov/projects/geochemical_landscapes/index.html
Page Contact Information: CMERSC Webmaster
Page Last Modified: 04-Mar-2013@14:35
