A MASS-BALANCE ANALYSIS OF PODZOLIZATION - EXAMPLES FROM THE NORTHEASTERN UNITED-STATES

The physical and chemical development of three Holocene-aged Spodosols, found in the northeastern United States on differing parent materials, was analyzed using mass-balance modeling in conjunction with complementary micromorphological and chemical techniques. The accumulation of soil organic matter, in combination with the process of past root growth, resulted in profile volumetric expansions of up to 86%. In all soils, expansion was greatest in Bhs horizons. Extensive mineral weathering and profile losses of Mg, Ca, Na, K, and Si occurred (10(2)-10(5) kg ha(-1)), concurrent with organic matter accumulations. Total cation losses were generally comparable to those measured in similar Holocene-aged soils, although losses varied somewhat between soils depending on the primary minerals present and their relative stabilities. Profile losses were also calculated for Fe, Al, and Mn and are comparable to those calculated in other regional studies; however, one soil clearly showed a net enrichment of Fe, presumably from external (i.e., atmospheric) sources. Other soils could be receiving such atmospheric additions as well. In all soils, Fe, Al, and Mn displayed zones of net pedogenic accumulation (in B and C horizons) below zones of net depletion (from overlying E and upper B horizons). From the standpoint of terrestrial C budgets, more carbon dioxide is apparently ''consumed'' by these soils through long-term organic C build-up (11-29 kg C ha(-1) yr(-1)) than is lost through long-term mineral weathering and inorganic C (bicarbonate) leaching (3-13 kg C ha(-1) yr(-1)).