| Continental shelf sediments are important locations not only for burial and mineralization of organic matter, but also for energy conversion and nutrient cycling during the early diagenesis. The sulfate reduction is important during the early diagenesis, which can account for more than 50% of the organic matter mineration. Continental shelf sediments are also important sites for the formation and burial of iron sulfides. Early diagenesis of sulfur and iron in marine sediments exerts a strong influence on global cycle of carbon, phosphorus, and interacteed trace elements, and, thereby, has important geochemical significance. The regulation of mariculture structure can influence the sulfide distribution. The sulfide can also jeopardize the mariculture environment conversely when it accumulated to some extent.This work mainly focus on the characteristics and influence factors of the reduced inorganic sulfur in sediments of the Yellow Sea (YS), East China Sea (ECS) and Sanggou Bay (SGB), and the main conclusions are:1. The acid volatile sulfide (AVS) concentration in sediments of the YS, ECS and SGB ranged from 0.01 to 17.14 μmol/g,0.01 to 25.02 μmol/g and 0.20 to 12.56 μmol/g, respectively. The AVS is relatively lower in surface and increased with increasing depth and then decline with depth. The peak value of AVS mainly present between 5 to 20 cm. The AVS concentration is especially lower at station T10 in ECS for sandy deposition. There was no peak value with increasing depth at station T02 in ECS possibly owing to the sample depth is not enough. The elemental sulfur (ES) concentration ranged from 0.02 to 44.40 μmol/g,0.14 to 27.75 umol/g and 0.16 to 1.10 μmol/g, respectively. The concentration was lower in the upper 10 cm, and increased with depth. And the ES concentration is relatively lower especially at the mouth of the SGB. The pyrite sulfur (pyrite-S) concentration in sediments of the YS, ECS and SGB ranged from 0.61 to 113.1 μmol/g,0.61 to 93.95 umol/g and 0.57 to 51.52 μmol/g, respectively. The concentration of pyrite-S was lower in the upper 5 cm at most stations, and then increased with increasing depth. Pyrite-S was the predominant sulfide mineral in sediments of the three regions, accounting for 16.1-99.0%,22.0-97.7% and 58.2-96.9% with mean of 72.5%,64.7% and 85.0%, respectively, of the reduced inorganic sulfur (RIS, sum of AVS, pyrite-S and ES). While for stations LDH and Wetland adjacent to the SGB, the AVS concentration is higher,264.72 and 191.64 μmol/g, respectively. There was a significance positive relationship between the ES and the pyrite-S (r=0.84, p<0.05; n=37) at these two sites, indicate that the pyrite formation through the polysulfide route.2. The ratios of AVS to pyrite-S is less than 0.3 at most stations in the YS, ECS and SGB, indicate the AVS can conversion to pyrite-S effectively. The AVS to pyrite-S ratio (e.g., stations P01, T06,38 and 35) increased progressively in sediments between 30 and 10 cm indicating either a transition to stronger reducing conditions or to more frequent occurrences of hypoxic or anoxic conditions at the study site in the ECS. The AVS can not effectively conversion to pyrite-S at station ST1 (below 5 cm) (in the SGB) and Wetland for shortage of ES.3. The reactive iron concentration in sediments of the YS, ECS and SGB ranged from 11.44 to 175.50 μmol/g,14.98 to 260.71 μmol/g and 17.79 to 148.26 umol/g with mean of 71.78 μmol/g,100.38 umol/g and 56.46±21.26 μmol/g. The concentration of reactive iron is higher than the Fe bounded with pyrite at most stations, and the degree of pyritization (DOP) is less than 0.6, indicate that the reactive iron can’t limit the pyrite formation. The DOP is relatively lower (<0.2) in surface, and lower than that in the normal marine sediments, but the concentration of reactive iron is higher than the Fe bounded with pyrite, and the pore water sulfate had no obvious decrease with depth. It suggestes that the availability of labile organic matter, but not reactive iron, is the limiting factor for pyrite formation. Though the concentration of reactive iron is low at stations C02 and A08 in the YS, the pyrite formation is also not limited by the amounts of reactive iron, indicate that the sulfide limit the pyrite formation at these two stations. While at station A04, reactive iron decreased by 84.2% with increasing depth, the DOP is higher than 0.65 below 20 cm, suggested lower concentrations of reactive iron limited the pyrite formation at lower layer. In addition, the reactive iron concentration ranged from 20.80 to 197.86 μmol/g at stations LDH and Wetland which adjacent to SGB, and declined with depth in upper 15 cm, then increased below that depth. The DOP increased with increasing depth at station LDH, and exceed 0.65 below 7 cm, suggested the reactive iron limit the pyrite formation at this station. It might be induced by the high SRR at lower layer.4. The pore water sulfate is high in the YS, ECS and SGB, with no obvious decline with increasing depth. At stations LDH and Wetland, the pore water sulfate concentration was low, it did not limit the sulfate reduction. The diffusive flux of pore water sulfate of the YS and the ECS ranged from 0.05 to 0.57 mmol/m2/d and 0.10 to 0.48 mmol/m2/d, respectively, and decreased from inshore to offshore. The diffusive flux of pore water sulfate in the ECS is also influenced by sulfate reduction rates (SRR). The SRR in the YS and ECS ranged from 1.06 to 8.85 μM/d and 2.00 to 40.60 uM/d, respectively, and decreased with depth in an exponential decay curve. In addition, the SRR increased with the increase of TOC concentration. The depth-integrated SRR (in the upper 28 cm) in the YS and the ECS ranged from 0.36 to 0.94 mmol/m2/d and 0.91 to 4.34 mmol/m2/d, respectively. And the contribution of sulfate reduction to organic matter minerazation in the YS and the ECS is 12.8-42.7% and 36.8-60.2%, respectively, suggested the sulfate reduction is an important path for organic matter mineralization in the YS and the ECS. The SRR is 1.89 mmol/m2/d in SGB, the contribution of sulfate reduction to organic matter minerazation is 42.1%. The SRR is 3.22 mmol/m2/d at station Wetland, which accounting for 20.7% of the organic matter mineralization.5. The concentration of reduced inorganic sulfur in sediments of SGB was negatively correlated with the dissolved oxygen concentration in near-bottom water, and positively correlated with the organic matter concentration, which is also influenced by different maricultre species. The organic matter concentration is higher in the scallop monoculture and the scallop/kelp polyculture than that in the kelp monoculture regions, consequently induced higher concentrations of reduced inorganic sulfur in these regions. Compared with the oyster monoculture area, the relatively lower organic matter and reduced inorganic sulfur accumulation in the scallop/kelp polyculture areas shows the environmental superiority of this culture practice. There was no evidence of a significant influence of mariculture on sulfide accumulation and the benthic environment after several years of mariculture in SGB. |
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