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Variation of dissolved fulvic acid from wetland measured by UV spectrum deconvolution and fluorescence excitation-emission matrix spectrum with self-organizing map
- Yu, Huibin, Song, Yonghui, Liu, Ruixia, Xi, Beidou, Du, Erdeng, Xiao, Shuhu
- Journal of soils and sediments 2014 v.14 no.6 pp. 1088-1097
- Cinnamomum camphora, fluorescence, fulvic acids, functional properties, grasslands, humification, infrared spectroscopy, lakes, land use, molecular weight, paddies, principal component analysis, soil depth, soil profiles, soil sampling, soybeans, wetland soils, China
- PURPOSE: UV spectrum with deconvolution (UVSD) and fluorescence excitation-emission matrix spectrum (FEEM) with self-organizing map have contributed to soil research by collecting more information from spectroscopic data. The aim of this study is to employ the USVD and FEEM with self-organizing map to determine structural composition and to evaluate the humification level of dissolved fulvic acid (FA) extracted from wetland soils under different types of land use. MATERIALS AND METHODS: Soil samples were collected from different depths in wetland ecosystems along a disturbed-impact gradient in Taihu Lake, China, i.e., Comm. Cinnamomum camphora (CCC), Comm. native grassland (CNG), paddy field (PFD), and green soybean field (SFD). RESULTS AND DISCUSSION: The Van Krevelen diagram of elemental analysis showed that FA was mainly associated with the surrounding terrestrial vegetation. The presence of characteristic functional groups in the FA was confirmed by Fourier-transformed infrared spectroscopy, consistent with the paradigm of humic substances. By the FEEM with self-organizing map, three fluorescent components were identified, and a fulvic-like material was a representative component in the FA fractions. The investigation of humification parameters deduced from the UVSD and FEEM with self-organizing map indicated that the aromatic content and molecular size of the FA decreased in the order of CCC > CNG > PFD > SFD. Principal component analysis verified that the humification level of the FA within the CCC soil profile was the highest, followed by the CNG, PFD, and SFD. Although an obvious variation occurred in the humification level within a given soil profile, no trend was observed with soil depth increment. CONCLUSIONS: The results of the present study demonstrate that UVSD and FEEM with self-organizing map are useful methods to investigate structural composition and to evaluate the humification level of the FA.