Properties of Alluvial Soils Impacted by Mine Tailings, Main Stem of the Coeur D' Alene River, Idaho.

Contaminants from mine wastes are deposited along alluvial area of rivers in many parts of the world, yet these areas remain important as sources of water for agricultural and urban areas, habitat for wildlife, and recreation.  Tailings produced from Ag, Pb, and Zn mining from the late 1800’s until nearly the present day were deposited on alluvial areas along the main stem of the Coeur d’Alene River in the Idaho panhandle.  Documentation of the properties of these soils was required in order to support new mapping and provide proper interpretations for soil survey users.  Ten pedons were described and horizons sampled along a 23 mile stretch within Kootenai County and soil properties characterized within the laboratory.   Surface deposition of mine wastes varied from 20 to 104 cm.  Clay content of both the spoil material and the underlying native alluvium was < 15%.  The similarity in particle size resulted in similar water retention, bulk density, and CEC between the two materials, with differences among horizons associated primarily with organic matter.  The spoil material was characterized by a high concentration of Fe, Mn, and trace elements such as Ag, Pb, Zn, Cu, Cd, and Hg relative to the native soil material.  These elements were vertically redistributed due to redox conditions in these soils.  Mineral form of the Fe and Mn were principally crystalline and non-crystalline (amorphous) oxyhydroxides.  These oxides were a sink for trace elements in these sediments.  The high oxide content of the mine tailings also resulted in high P fixation capacity and increased fertilizer requirements to maintain vegetative productivity.