Geochemical and Mineralogical Maps, with Interpretation, for Soils of the Conterminous United States

READ ME

Nickel (Ni) is a metallic trace element used extensively in the production of stainless steel, nonferrous alloys, and superalloys, used to make parts for gas turbine engines. Other uses include rechargeable nickel–cadmium (Ni–Cd) batteries, coinage, and catalysts. Nickel is essential for some bacteria, plants, and domestic animals, and humans; although in large doses Ni can be toxic to humans. More information about the toxicity of Ni (or other elements and substances) and its potential negative human health impacts can be found at the Agency for Toxic Substances and Disease Registry (ATSDR) website, or click to download a fact sheet about Ni.

Nickel occurs primarily in sulfide minerals, but also may form arsenides and antimonides. It frequently substitutes for iron (Fe) or magnesium (Mg) in minerals such as olivine, pyroxene, amphibole, and garnet. In soils, Ni may be associated with Fe and manganese (Mn) hydroxides and it has a tendency to sorb onto clay minerals and organic matter.

The average abundance of Ni in the Earth's upper continental crust is estimated to be 34 milligrams per kilogram (mg/kg) (Hu and Gao, 2008). Ultramafic rocks, such as serpentinite and peridotite, have highly elevated concentrations of Ni with concentrations as much as a few thousand mg/kg. Mafic rocks, such as basalt, have an average Ni concentration of about 130 mg/kg. Among the other common rock types, shale has elevated Ni with an average concentration of about 70 mg/kg. In contrast, the average Ni concentration is only about 2 mg/kg in sandstone and about 5 mg/kg in limestone and granite.

The distribution of mineral resource deposits with Ni as a commodity (major or minor) in the United States, extracted from the U.S. Geological Survey (USGS) Mineral Resource Data System (MRDS) website, can be seen by hovering the mouse here. Statistics and information on the worldwide supply of, demand for, and flow of Ni–bearing materials are available through the USGS National Minerals Information Center (NMIC) website.

In our data, the median Ni concentration is slightly higher in the soil C horizon (16.7 mg/kg) than in the soil A horizon (13.8 mg/kg) and the top 0- to 5-cm layer (13.5 mg/kg) (see the summary statistics [open in new window]). This indicates that Ni is somewhat mobile in the near–surface weathering environment. In general, the geochemical maps for the three sample types are quite similar for Ni.

The distribution of Ni in soils of the conterminous United States is primarily controlled by the composition of underlying soil parent materials. Areas of elevated Ni concentrations in soils are seen in:

• Northern California, Oregon, western Washington, central Maryland, extreme southeastern Pennsylvania, central and western North Carolina, northeastern Minnesota, and central Arizona, where parent materials for soils are, at least in part, ultramafic or mafic rocks or glacial deposits derived from these rock types; and
• Eastern Montana, North Dakota, South Dakota, Iowa, eastern Nebraska, eastern Kansas, northern Missouri, Illinois, Indiana, Kentucky, Ohio, and Pennsylvania, where parent materials are dominantly marine shale, clayey till or glacial deposits containing a significant amount of shale

The Gulf and Atlantic Coastal Plain (Fenneman and Johnson, 1946) is bisected by the Southern Mississippi River Alluvium and the Southern Mississippi Valley Loess (USDA, 2006). Alluvial sediments have deposited in the Mississippi River valley as the river flooded in recent geologic time. When these sediments dried, winds picked up the fine material and deposited it in thick loess sheets, mainly along the east side of the river valley. The youngest loess sheets are about 10,000 years old. A pattern of higher Ni concentrations in soils developed on these young sediments reflects long–range transport of Ni–bearing material from the upper part of the Mississippi River drainage basin.

Areas of low Ni concentrations in soils include:

• Gulf and Atlantic Coastal Plain (Fenneman and Johnson, 1946) where parent materials are dominantly quartz–rich sedimentary rocks and unconsolidated sediment;
• Nebraska Sand Hills (USDA, 2006), where parent materials are quartz– and plagioclase–rich, unconsolidated sand dunes and sand sheets; and
• Southern High Plains (USDA, 2006) of eastern New Mexico and Texas where parent materials are quartz–rich eolian sands and alluvial sediments.

Statistics - 0 TO 5 CM

Histogram

Boxplot

Empirical cumulative distribution function

Statistics - A Horizon

Histogram

Boxplot

Empirical cumulative distribution function

Statistics - C Horizon

Histogram

Boxplot

Empirical cumulative distribution function