Contributions of Oi, Oe and Oa horizons to dissolved organic matter in forest floor leachates

The aim of this study was to identify the role of organic matter of the Oi, Oe and Oa layers for leaching of dissolved organic matter (DOM) from the O horizon in a podsolised forest soil in southern Sweden. Solid state C-13 cross polarization magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectroscopy and C-14 measurements were used to analyse organic matter in solid material and water extracts from the Oi, Oe and Oa horizons, soil leachates collected below the Oe and Oa horizons and throughfall. The DOM in soil leachates from the Oe horizon had a C-14 content that was higher than the water extractable organic matter (WEOM) from the Oi horizon but equal to the C-14 content in the WEOM from the Oe horizon. The C-14 contents in WEOM and DOM from the Oe and Oa horizons were all equal. These results suggest that the DOM leaving the Oe horizon to a large extent had its origin within the Oe horizon itself. NMR spectroscopy showed that WEOM was higher in O-alkyl and lower in aromatic carbon than DOM in soil leachates. (C) 2002 Elsevier Science B.V All rights reserved.