沉积物活性铁锰特征对比研究及其对有机碳矿化的意义 以长江口、黄海中部陆架泥质区和黄河口为例

韦世金; 孟倪; 韦钦胜; 庄光超

doi:10.12362/j.issn.1671-6647.20230823002

沉积物活性铁锰特征对比研究及其对有机碳矿化的意义以长江口、黄海中部陆架泥质区和黄河口为例

Comparative Study on the Characteristics of Reactive Iron and Manganese in Sediments From Coastal China and Its Significance for Organic Carbon Mineralization: Case Studies at the Yangtze River Esturary, the Mud Area of the Shelf in Central Yellow Sea, and the Yellow River Esturary

摘要

摘要: 铁锰的早期成岩是海洋沉积物有机碳矿化的重要途径之一，活性铁锰的含量和分布情况对评估铁锰异化还原作用下的有机碳矿化具有重要意义，然而目前针对中国近海不同沉积环境下活性铁锰的分布对比研究还比较少。2021年8—9月长江口（CJK1-3）、黄海中部陆架泥质区（YSCW-1）和黄河口（NS-37）三个站位沉积物中活性铁锰的含量及分布特征显示，长江口沉积物中碳酸盐结合态铁（Fe_carb）的平均质量摩尔浓度（91.23 μmol·g⁻¹，干重）分别为黄海中部陆架泥质区沉积物（19.35 μmol·g⁻¹，干重）和黄河口沉积物（14.15 μmol·g⁻¹，干重）的4.71倍和6.45倍，无定形和弱结晶铁氧化物（Fe_ox1）的平均质量摩尔浓度顺序为CJK1-3（111.63 μmol·g⁻¹，干重）>YSCW-1（79.99 μmol·g⁻¹，干重）>NS-37（61.63 μmol·g⁻¹，干重）。3个站位沉积物中锰氧化物的质量摩尔浓度都低于铁，可还原态锰（Mn_re）平均质量摩尔浓度分别为Fe_ox1的1.56%、0.91%和2.29%。培养实验结果表明铁锰异化还原在原位有机质条件下发生，铁锰异化还原的评估结果表明铁异化还原是近海（河口）沉积物有机碳矿化的重要途径，而锰还原是次要途径。研究结果加深了对中国近海（河口）沉积物中铁锰生物地球化学的认识。

Abstract: The early diagenesis of iron and manganese is one of the important pathways of organic carbon mineralization in marine sediments. The details of content and distribution of reactive iron (Fe) and manganese (Mn) are of great significance to evaluating organic carbon mineralization contributed by dissimilatory Fe and Mn reduction in sediments. However, so far, few studies have investigated the distribution of reactive iron and manganese in different sedimentary environments of coastal China. The molality of reactive Fe and Mn in sediments from the Yangtze River Estuary (CJK1-3), the mud area of the shelf in central Yellow Sea (YSCW-1) and Yellow River Estuary (NS-37) was investigated based on the sequential extraction procedures in this study. The relevant biogeochemical analysis was conducted with the depth profiles of Fe and Mn in the sediment gravity cores. Results showed that the mean molality of carbonate-bound iron (Fe_carb) in sediments from the Yangtze River Estuary was 4.71 times and 6.45 times higher than that from the mud area of the shelf in central Yellow Sea (19.35 μmol·g⁻¹, dry weight) and Yellow River Estuary (14.15 μmol·g⁻¹, dry weight), respectively. The mean value of amorphous and poorly crystalline Fe(III) oxides (Fe_ox1 ) showed the following decreading trend, CJK1-3 (111.63 μmol·g⁻¹, dry weight) >YSCW-1 (79.99 μmol·g⁻¹, dry weight) >NS-37 (61.63 μmol·g⁻¹, dry weight). The molality of Mn oxides was lower than that of iron in all three stations, and the mean molality of reducible manganese (Mn_re) accounted for 1.56%, 0.91% and 2.29% of Fe_ox1, respectively. The results of the incubation experiment showed that dissimilatory Fe and Mn reduction occurred under the condition of in-situ organic matter. The evaluation results of dissimilatory Fe and Mn reduction indicated that dissimilatory Fe reduction was a major pathway for organic carbon mineralization in coastal (Estuary) sediments, while Mn reduction was a minor one. The results of this study provide some new insights for iron and manganese biogeochemistry in coastal (estuarine) sediments of China.

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