Spectral features of humic substances in a perhumid subtropical montane forest ecosystem, Taiwan

Abstract

The optical characteristics of humic acids (HAs) and degree of humification of humic substances in Albaquults, Dystrochrepts, and Histosols of a perhumid forest in Taiwan were studied. Values of the humification indexes (E4/E6 ratios) of both the total soil extract and HA fractions gave similar results in the case of surface layers (0 horizons), whereas in the case of the mineral horizons, those of the total soil extract were not significantly correlated with the results obtained for the HA fraction. The profile distribution of the values of the FA/HA ratio increased from top to bottom, indicating that the FAs (fulvic acids) were more mobile than the HAs and accumulated in deeper mineral horizons. The pronounced migration of the FAs contributed to the lower degree of humification of humic substances in the mineral horizons. The ΔlogK and RF values of the HAs showed that the HAs in the mineral horizons of the soils were less humified (classified as Rp type) than those of the 0 horizons (classified as Rp or P type). The predominance of the P type of HAs in this studied site suggests that there is a high degree of humification in perhumid forest soils which are with high rainfall and extreme acidity. There is no significant effect of topography on the type of HAs that developed along the slope sites.