## 3 Materials and Methods  
### Description of Field Sites and Samples  
A total of 129 soils from four sources across the United States were utilized for this project--50 samples from non-irrigated land in central New Mexico, 21 soil samples from two sites in west-central New Hampshire, and 58 soils from small arms ranges on military installations in Massachusetts, Virginia, Georgia, Idaho, Washington, and Alaska. Each sample was sieved and homogenized, with fine-grained aliquots hydraulically pressed into pellets for analysis.  
In the U.S., soils are classified by the Natural Resources Conservation Service (NRCS) on the basis of physical and chemical properties in their different horizons (e.g., composition, color, texture, structure, etc.) from the surface to a depth of two meters. The NRCS soil taxonomy establishes hierarchies of classes to permit the relationship among soils and between soils, and the factors responsible for their character, to be understood. The soil series is the lowest category within soil taxonomy. All soils within a single series have uniform differentiating characteristics and arrangement of horizons. This does not mean that all soils within a series are identical; it does mean that they have a similar sequence of horizons, but the horizons may be of different thickness, color, and structure, within prescribed limits. All of the soils within a series will have developed in the same kind of parent material with comparable drainage characteristics and will be of similar age. The effects of climate and biological activity will have been very similar. Consequently, the soils within a series exhibit like properties and respond in like fashion to usage or manipulation.  
Compositionally distinct soil series were sampled from six locations across central-north New Mexico that formed the primary suite of samples for this work. The six soils sampled were (i) the loamy fine sand of the Bluepoint Soil Series at the Rio Salada, (ii) the very stony sandy loam of the Laborcita-Pilabo-Lemitar Soil Series Complex in Upper Socorro Canyon, (iii) the very stony sandy loam of the Laborcita-Pilabo-Lemitar Soil Series complex in Lower Socorro Canyon, (iv) the gravelly sandy loam of the Millett-Sedillo Soil Series complex at Sedillo Hill, (v) the gypysiferous sand of the Lark-Transformer Soil Series association at White Sands, and (vi) the strongly saline silty clay loam of the playa soil at Willard. These soils were sampled from the upper 10 cm of the surface soil profile and analyzed in January 2019.  
An additional 58 soil samples came from six US military installations--Ft. Wainwright, AK; Ft Lewis, WA; Idaho National Guard Camp Kinama; Ft. Benning, GA; Ft. Eustis, VA; and Massachusetts Military Reservation/Joint Base Cape Cod. These soils were collected from the top 2.5 cm of soil at individual firing ranges and, therefore, are contaminated to various extents with metal elements present in munitions such as Cu, Zn, Pb, W, and Sb. A range of soils, varying from uncontaminated to strongly contaminated, were analyzed for each of the six military installations. These six soil groups were analyzed in March-April 2019.  
Finally, six samples of soil were collected from the upper 5 cm of soil at two locations in central New Hampshire, three samples from the site of the USACE-ERDC Cold Regions Research & Engineering Laboratory in Lebanon, NH and three samples from the Bean Hill locality in Belmont, NH. Two separate pellets were prepared from each of these soil collections to create a data set that consisted of six'samples' per class. Additionally, three soil pits were excavated at each of the Bean Hill sample sites, with the different soil horizons in each pit described and sampled. The Bean Hill areas have been mapped as belonging to three NRCS soil series--Canterbury fine sandy loam, Moosilaukee fine sandy loam, and Pillsbury fine sandy loam.