Abstract: Ultraviolet/visible spectroscopy and fluorescence spectroscopy were used to describe the spectral characteristics of soil dissolved organic matter (DOM) in four typical coastal wetlands i.e. Spartina anglica, Suaeda glauca, Phragmites australis and Robinia pseudoacacia wetlands in Yancheng, China. The results show that the aromatic index (SUVA₂₅₄) of soil DOM under Robinia pseudoacacia community was significantly higher than that of other wetlands. Except for Suaeda Glauca wetland, the SUVA₂₅₄ values of DOM in the topsoil of all other wetlands were significantly higher than that in the soil of depth. The fluorescence efficiency (FE) of soil DOM was significantly different between soil layers and increased with soil depth, and also significant negative correlated with SUVA₂₅₄. In the >25-40 cm soil depth, the FE value of DOM in Phragmites Australis wetland was significantly higher than that in other wetlands. The FI values of soil DOM under the four vegetation communities were all less than 1.40, which indicates that the terrestrial input of DOM played a dominant role. The humification index (HIX_syn) value of soil DOM was higher in Spartina Anglica wetland, while the HIX_syn of Robinia pseudoacacia wetland showed significant differences between soil layers. Moreover, the SUVA₂₅₄ values of DOM were positively correlated with soil organic carbon, dissolved organic carbon and C/N ratio, respectively. Our findings indicate that the aromatization and humification of DOM were higher in the topsoil of Robinia pseudoacacia and Spartina Anglica wetlands, respectively, and suggest that there are more complex compounds in the topsoil in these wetlands.

Key words: dissolved organic matter, chemical structure, spectral characteristics, coastal wetlands