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Early diagenesis in marginal sea sediments is an important process that affects carbon cycling and burial. Early diagenetic processes and influencing factors, however, remains poorly constrained. Dissolved inorganic carbon (DIC), dissolved inorganic nitrogen (DIN), Fe2+, Mn2+, sulfate and other parameters in sediment porewaters of five short cores collected in August 2018 from the Changjiang River Estuary and East China Sea inner-shelf were analyzed. In combination with grain size composition, specific surface area, organic carbon concentrations and stable carbon isotopic composition in surface sediments and bottom water parameters, the early diagenetic processes and influencing factors in sediments under different sedimentary regimes were studied. Concentrations of DIC and ${{\rm {NH}}_4^+} $ in sediment porewaters in the mud area gradually increase with depth, and relatively high production fluxes of DIC and ${{\rm {NH}}_4^+} $ (4.03 mmol/(m2·d) and 0.57 mmol/(m2·d), respectively) and consumption fluxes of ${{\rm {SO}}_4^{2-}} $ (−4.56 mmol/(m2·d)) are observed at the center of the mud area, while in the sandy area, there are no obvious variations of these solutes, and the fluxes are lower compared with those in muddy sediments. According to the vertical distributions of these solutes in the sediment porewaters, the sediment disturbance depth in the mud area varies at 20−40 cm, and gradually decreases from the Changjiang River Estuary mud area to the Zhe-Min coast mud area, whereas in the sandy area, no sediment disturbance is found. The thickness of sediment disturbed layer is positively correlated with solute fluxes (e.g., DIC and ${{\rm {NH}}_4^+} $) in sediment porewaters, indicating that the physical reworking of sediments is an important factor affecting the remineralization of sedimentary organic carbon in the mud area. In general, the main decomposition pathway of the sedimentary organic carbon in the disturbed layer of the mud area is iron/manganese reduction, and below the disturbed layer the main pathway is the sulfate reduction, while in the sandy area, the main degradation pathway is aerobic respiration. This study enriches the understanding of the impact of sedimentary dynamic processes on early diagenesis in the Changjiang River Estuary and adjacent sea areas, and contributes to better understand the cycling and burial of organic carbon in the large-river estuary and adjacent sea areas.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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