Continental United States Atmospheric Wet Calcium Deposition and Soil Inorganic Carbon Stocks

Organic and inorganic soil C pools are major components of the global C budget, yet they are still poorly estimated and understood. This study ranked atmospheric wet Ca2+ deposition from 1994 to 2003 within the continental United States by soil order using spatial analysis of Ca2+ wet deposition data and a state soil geographic database. The total average annual atmospheric wet deposition (AAAWD) of Ca2+ within the continental United States was 8.6 x 108 kg, which would be equivalent to the theoretical formation of 2.6 x 108 kg C as soil inorganic C (SIC), barring losses from erosion and deep leaching. The soil orders receiving the highest area-normalized total AAAWD of Ca2+ were: (i) Alfisols (172 kg km-2 Ca2+), (ii) Mollisols (170 kg km-2 Ca2+), (iii) Histosols (168 kg km-2 Ca2+), and (iv) Vertisols (157 kg km-2 Ca2+). Barring losses from erosion and leaching, these Ca2+ wet deposition fluxes would equate to the theoretical formation of the following amounts of area-normalized total C equivalents in the pedon: (i) Alfisols, 52 kg C km-2; (ii) Mollisols, 51 kg C km-2; (iii) Histosols, 50 kg C km-2; and (iv) Vertisols, 47 kg C km-2. The sequestration of SIC has been shown to be important in soil orders of nonarid regions, particularly in Mollisols and Alfisols.