Proposed Geochemical Family Classification in Soil Taxonomy.

Few locations have soils not impacted in some way by man and soil survey is expanding its efforts to document these impacts on soil properties.  Trace elements are commonly added to soils from a variety of land uses in both urban and rural environments.  These additions become permanent features of the soils and can pose a significant negative influence on future land use and management.  Trace element contamination is a significant feature impacting human health and should be recognized within both soil survey and classification.  The objectives of this poster are to (1) propose a possible method for geochemical classification of soils within Soil Taxonomy (ST), and (2) evaluate and test these criteria on a variety of soils.  The proposed classification would assign a designation at the family level within ST for soils that contain one or more trace elements at concentrations greater than a specific threshold within the upper 100 cm of mineral soil.  This threshold level is established by calculating the native (background) geochemical concentration at the 95^th percentile using a wide range of soil types analyzed within the USDA-NRCS National Cooperative Soil Survey Characterization database.  For example, Pb has a median and 95^th percentile concentration of 9.4 and 26.2 mg kg^-1, respectively.  The proposed taxonomic limit for Pb is 50 mg kg^-1, above which the term “metallic” is added to the family name in ST.  The resulting criteria were tested on a number of anthropogenically-altered urban and rural soils within the database and these criteria successfully flag soils that have concentrations of trace elements at concentrations that may warrant concern depending on land use.