Chemical and spectroscopic characterization of dissolved humic substances in a mangrove-fringed estuary in the eastern coast of Hainan Island, China

摘要

Mangrove-derived dissolved organic matter (DOM) has an important effect on estuarine and coastal area on a large scale.In order to improve the understanding of origin,composition,and fate of DOM in mangrove-fringed estuarine and coastal areas,dissolved humic substances (DHS) were isolated from one mangrove pore-water sample and one near-shore seawater sample downstream the mangrove pore-water site in the eastern coast of Hainan Island,South China.Fulvic acids,humic acids and XAD-4 fractions were obtained from the two water samples by using a two-column array of XAD-8 and XAD-4 resins.Chemical and spectroscopic methods were used to analyze the features of these DHS.Compared to the mangrovepore-water DHS,the near-shore seawater DHS were found rich in 13C with lower C/N ratios and more aliphatic compounds and carbohydrates,but less aromatic structures and carboxyl groups.As for the three fractions of the two DHS,XAD-4 fractions contain more aliphatics,carbohydrates,carboxyl groups,and enrich in 13C with respect to both fulvic and humic acids.Photo-oxidation transformation and contribution from marine-derived DOM were considered as the main reasons resulted in the difference in compositional features for these DHS in this study.