Geochemistry of reduced inorganic sulfur, reactive iron, and organic carbon in fluvial and marine surface sediment in the Laizhou Bay region, China

Abstract

Understanding the geochemical cycling of sulfur in sediments is important because it can have implications for both modern environments (e.g., deterioration of water quality) and interpretation of the ancient past (e.g., sediment C/S ratios can be used as indicators of palaeodepositional environment). This study investigates the geochemical characteristics of sulfur, iron, and organic carbon in fluvial and coastal surface sediments of the Laizhou Bay region, China. A total of 63 sediment samples were taken across the whole Laizhou Bay marine region and the 14 major tidal rivers draining into it. Acid volatile sulfur, chromium (II)-reducible sulfur and elemental sulfur, total organic carbon, and total nitrogen were present in higher concentrations in the fluvial sediment than in the marine sediment of Laizhou Bay. The composition of reduced inorganic sulfur in surface sediments was dominated by acid volatile sulfur and chromium (II)-reducible sulfur. In fluvial sediments, sulfate reduction and formation of reduced inorganic sulfur were controlled by TOC and reactive iron synchronously. High C/S ratios in the marine sediments indicate that the diagenetic processes in Laizhou Bay have been affected by rapid deposition of sediment from the Yellow River in recent decades.

Spatial variation in bacterial community in natural wetland‐river‐sea ecosystems

“…This suspended sediment contains iron, nitrogen, and other elements, and is potentially important for nutrient accumulation in marine sediment. Previous work and our preliminary study have shown that total iron (Fe), ferrous iron (Fe(II)), ferric iron (Fe(III)), and ammonium (‐N) are present in higher concentrations in the coastal marine sediment than in the estuarine sediment of the Yellow River, whereas nitrate (‐N) concentration is higher in the estuarine sediment than in the coastal marine sediment. Hence, we hypothesize that the biogeographic distribution of bacterial communities is related to spatial distance, hydrology and environmental variables and that different environmental variables have profound effects on bacterial community structure in different habitats.…”

Coupling mechanisms of S–Fe–P in surface sediments under the stresses of high salinity and heavy metals in coastal rivers

“…The fractions of RIS mainly include AVS (fraction of sulfides that are extracted by hydrochloric acid), CRS (pyritic sulfur), and ES (a combination of oxidation products of AVS with O 2 , Fe oxides, and Mn oxides). RIS was conducted using a modified version of the procedure that was described by Sheng et al (2015). AVS, CRS, and ES were separated sequentially by 6 M HCl, acidic Cr(II), and Cr(II) plus N,Ndimethylformamide (DMF), respectively, using pure N 2 as a carrier gas to purge and trap H 2 S at 60 ± 1 °C.…”

“…Additionally, sulfides can be reoxidized into elemental S (ES) by Fe(III) (oxyhydr) oxides (FeOOH) under anoxic conditions, thereby inducing chemical Fe reduction and remobilization of previously bound P (FeOOH-P) (Pan et al 2019). After being released into porewater, the reduced Fe(II) can precipitate with the dissolved sulfide as acid volatile sulfur (AVS, FeS) and react with ES to form chromium reducible sulfur (CRS, FeS 2 ) (Sheng et al 2015). The accumulated reductive S and Fe minerals have minimal affinity for P sequestration (Thouvenot-Korppoo et al 2012).…”

“…Acid volatile sulfur and CRS are the primary fractions of RIS in coastal sediments. The ratios of AVS/CRS, the degree of pyritization (DOP), and the degree of sulfurization (DOS) can be used to distinguish whether pyrite and Fe sulfide formation is C-or Fe-limited (Sheng et al 2015) and to identify the completeness of the reaction of RFe with aqueous sulfide (Kraal et al 2013). Previous studies have focused on S-Fe-P coupling under the influence of redox conditions (e.g., tidal inundation and eutrophication) in coastal ecosystems (Sakai et al 2013;Sun et al 2016), but few studies have been conducted on the mechanisms and controlling factors of S-Fe-P under the stresses of high salinity and heavy metals.…”

The differentiation of iron-reducing bacterial community and iron-reduction activity between riverine and marine sediments in the Yellow River estuary

“…It is also has the second largest sediment load flux to the ocean of any river (Poulton and Raiswell 2002;Pan et al 2013). Previous studies (Liu et al 2003;Qiao et al 2007;Gong et al 2015;Sheng et al 2015;Zhang et al 2017) have shown that the concentrations of ferrous iron (Fe(II)), ferric iron (Fe(III)), total iron (Fe), and ammonium (NH 4 + -N) were higher in the coastal marine sediment than in the Yellow River sediment, whereas the concentration of nitrate (NO 3 − -N) was higher in the riverine sediment than in coastal marine sediment. Patterns of IRB abundance and diversity can indicate their contribution to the biogeochemical cycles, while changes in community structures are associated with spatial variations in nutrients [i.e.,NO 3 − -N, NH 4 + -N, Fe(II), Fe(III)] in different habitats.…”