Composition of organic sulfur in riverine and marine sediments: Insights from sulfur stable isotopes and XANES spectroscopy

• Published in: Organic geochemistry Vol. 99; pp. 102 - 112
• Main Authors: Zhu, Mao-Xu, Chen, Liang-Jin, Yang, Gui-Peng, Huang, Xiang-Li, Zhao, Yi-Dong
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2016
• Subjects: absorption; East China Sea; estuaries; eutrophication; fulvic acids; humic acids; Jiaozhou Bay; marine sediments; mineralization; Organic sulfur; Sediments; stable isotopes; sulfides; sulfur; Sulfur isotopes; watersheds; X-radiation; X-ray absorption spectroscopy; XANES; Yangtze River; East China Sea; Yangtze River; Organic sulfur; Sulfur isotopes; Jiaozhou Bay; Sediments; XANES; East China Sea
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/j.orggeochem.2016.07.002

•Organic sulfur (OS) in sediments characterized from S isotopes and XANES.•Highly reduced fulvic acid S (FA-S) not enhanced by sulfurization.•Humic acid S (HA-S) in marine sediments dominated by terrigenous OS.•Humic-S is structurally and isotopically different from non-Cr reducible OS. Sulfur isotopes and X-ray absorption near edge structure (XANES) spectroscopy were combined to characterize/compare three operational organic sulfur (OS) pools, i.e. fulvic acid sulfur (FA-S), humic acid sulfur (HA-S) and non-chromium reducible organic sulfur (non-CROS) in marine [the East China Sea (ECS) and Jiaozhou Bay (JZB)] vs. riverine [Yangtze River (YR) and JZB tributaries] sediments. XANES results indicate that in marine sediments high valency S was the dominant OS functionality in both HA-S and FA-S, while non-CROS was dominated by low valency OS (80–92%). In the riverine sediments FA-S was dominated by high valency OS, while the average fractions of low and high valency OS in HA-S were comparable. The isotopic composition of FA-S (δ34SFA-S) and HA-S (δ34SHA-S) indicated that a substantial fraction of sulfide was incorporated into FA via sulfurization in the marine sediments, whereas terrigenous OS was almost the sole important source of HA-S. Compared with the ECS sediments, JZB sediments had more depleted 34SFA-S and a higher fraction of highly reduced FA-S due to eutrophication induced sulfurization. Relative to riverine FA-S, substantial sulfurization had not resulted in an increase in the fraction of highly reduced FA-S in marine sediments. This implies that the terrestrial systems may be much more favorable for the formation and/or preservation of highly reduced biogenic FA-S than the marine settings. The fraction of highly reduced HA-S in the JZB and its tributaries was similar, whereas the fraction was much lower in the ECS than in the YR. This indicates that highly reduced HA-S moieties in the YR may have been subject to extensive mineralization loss during transport in the large riverine/estuarine system, whereas the process in the JZB tributaries may be much weakened due to a relatively small catchment area. Distinct differences in isotopic and structural composition between humic-S (FA-S+HA-S) and non-CROS in the ECS sediments indicate that a combination of S isotopes and S-XANES is needed for characterizing the two operational pools for a better understanding the nature of OS in the ocean.