Mechanisms of alkaline buffering by peat and quantitative estimation of its buffering capacity

The alkaline buffering capacity of humic substances in persistent organic materials such as peats has been utilized for remediation of alkaline soils. The purposes of the present study were to reveal the mechanism of alkaline buffering and to quantify the alkaline buffering capacity of humic substances contained in three peat samples obtained from Hokkaido, Canada, and Sri Lanka. Acidic functional groups in humic acid and fulvic acid extracted from the three natural peats were quantified by alkalimetric titration and pK distribution analyses of the titration curves. The results indicate that the inherent degree of humification of the organic matter can be identified from the pK distribution, which showed that the humic substances in peats contained diprotic acids. The present study also showed that the ratios of amounts of deprotonation to organic carbon content, as well as the organic carbon content, were needed for quantification of the pH buffering capacity. Moreover, the study showed that the composition of the peat from Sri Lanka was different from those of other peats and that it is a effective organic material for buffering under alkaline conditions.