| Multiple spodic (Bh) horizons in soils are common in the thick, acid sands of the Osceola National Forest, Northeast Florida. Spodosols samples were taken along a 200 m upland-lowland transect. Podzolization explained how the upper spodic horizon was formed. The lower one, usually extensive, and permanently saturated with water, did not follow the same mechanism of formation. The significance of this lower subsurface horizon has increased greatly as scientists study new ways of decreasing atmospheric carbon dioxide (CO2), using soils as sinks, to reduce the "greenhouse effect". Carbon (C) stored in multiple-layered Spodosols is greatly underestimated since soil scientists limit their studies to the first 2 m. Carbon-14 ( 14C) dating indicated that the upper spodic horizon was 1,810 +/- 40 years old; the lower B'h1 was 15,270 +/- 370 years old and the lower B'h2 was 13,820 +/- 60 years old. Aluminum (Al) illuviation occurred in the upper Bh, but not in the lower B'h horizon. Humic/fulvic acid (HA/FA) ratios were different for both upper and lower Bh horizons. The upper Bh was dominated by fulvic acids (FA) (59% vs. 41%) and the lower B'h horizon was dominated by humic acids (HA) (61% vs. 39%). C/Al ratios decreased with depth in the upper Bh horizon, but increased with depth in the lower one. This lead to the conclusion that the mechanism that immobilizes C to form the different Bh's horizons is different. The pedogenic process of podzolization occurred in the upper Bh horizon. In the lower B'h horizon, the theory of formation was as follows: fulvic acids, after accumulating in the saturated zone, reacted with the Al in the coatings of the sand grains without stripping the coatings. The FA were responsible for darkening the sand grain. The HA reacted mostly with the Al and clays in solution. They precipitated as Al-humates and filled the space in between the sand grains as black sediment. Genesis of Spodosols is a direct manifestation of the processes dictating the terrestrial fate and transport of C. To understand these processes is fundamental in the assessment of global C dynamics. |
