Chemical and spectral differences in humic matter from swamps, streams and soils in the southeastern United States

Abstract

There are differing opinions about the characteristics of humic matter from streams and soils. This study was conducted to determine and compare the chemical properties of humic matter from the Okefenokee swamp, Satilla river, Ohoopee river, and surrounding soils in the Georgia Coastal Plain, USA. Humic (HA) and fulvic acid (FA) were isolated from water by XAD resin and conventional NaOH methods and from soil samples by the NaOH method. The humic fractions were analyzed for total acidity, COOH, C, H, and N contents. Liquid 13C NMR and infrared analysis were performed to determine the structural composition. The humic matter isolated from swamp and river water using XAD resin comprised of 72% FA and 28% HA, and that isolated using NaOH comprised of 60–70% FA and 30–40% HA. In contrast, humic matter extracted from soils with NaOH was 80% HA and 15% FA. The C and H contents, and spectral characteristics of HA (or FA) isolated by the XAD resin method from the swamp and river waters were similar. However, integration of NMR spectra yielded data indicating that HA from the Okefenokee swamp was more aromatic than that from river water. The conventional NaOH method yielded HA (or FA) with lower C, H and N contents, and smaller total acidity than the resin method. HA isolated by NaOH extraction from Okefenokee swamp was less aromatic than HA extracted using XAD resin, and structural differences, which may have occurred as a result of NaOH extraction, were detected by infrared spectroscopy. The conclusion was made that the NaOH method was an equally valid method as the resin method. No conclusive evidence was obtained to support the hypothesis that soil HA was more aromatic than aquatic HA. A strong signal at 55.8 ppm in the NMR spectra of black water HA, attributed to -OCH 3, implied the presence of a common source component incorporated in the humic molecule of black water and soils.