【作者】 闫慧敏；

【导师】 刘敏； 许世远；

【作者基本信息】 华东师范大学 ， 自然地理学， 2008， 硕士

【摘要】 Si是海洋初级生产力主要贡献者——硅藻生长所必须的营养元素。生物硅(BSi)主要由海洋真光层硅质浮游生物(硅藻等)产生,沉积物中BSi的积累能够反映上层水体生产力的时空变化,它的赋存与分解对滨岸地区富营养化问题的发生影响巨大。本文以长江口滨岸潮滩为典型对象,研究沉积物中BSi的时空分布规律,分析了沉积过程中BSi的转化和积累效应,并结合盐沼植物分析植物对BSi的富集作用,试图阐述BSi在长江口潮滩湿地的分布及富集机制。取得了以下研究成果:长江口滨岸潮滩表层沉积物中BSi的含量具有明显的时空变化差异:边滩表层沉积物二月份BSi的含量在0.46%～1.61%之间,总体上具有自陆向海逐渐增加的趋势,八月份BSi的含量在0.39%～1.36%之间,其沿程分布模式与二月份相反;沙洲沉积物中BSi含量的变化范围为0.47%～1.02%,向口门方向具有逐渐增加的变化趋势,且不同沙洲高、中、低潮滩BSi含量变化存在显著性差异。沉积物理化性质与BSi之间的相关分析揭示,BSi含量与沉积物机械组成、有机质含量有密切关系,在细颗粒且富含有机质的沉积物中易于BSi的累积和赋存。此外,底栖硅藻可能是潮滩表层沉积物中BSi的重要来源。利用弱酸弱碱分级提取法测定柱状沉积物BSi含量发现:来自氧化外壳的Si-HCl含量明显低于内部的Si-Alk,与以前的研究结果相比,弱酸前处理显著提高BSi的提取量。粒径效应分析显示:不同粒径下BSi的垂向变化趋势也不一样,在125-250μm和63-125μm粒径下沉积物中BSi都随深度呈现逐渐增加的变化趋势,而在＜63μm粒径下则是逐渐降低,并且Si-HCl和Si-Alk平均含量随粒径的减小逐渐降低;受植物生长影响高潮滩和中潮滩30cm柱状沉积物中BSi含量都显著高于低潮滩,最高值都是在植物生长最旺盛的八月份达到,并且在不同的月份下Si-HCl和Si-Alk都有不同的变化规律。分析显示,无论是Si-HCl还是Si-Alk都与有机碳、有机氮含量存在非常明显的线性相关关系,暗示了BSi在沉积埋藏过程中与有机质之间存在密切关系。盐沼植物芦苇和海三棱蔗草生长季过程中对BSi表现为强富集作用,尤其是芦苇叶BSi含量在生长过程中几乎线性累积,生长季末期高达4.86%。互花米草各组织内BSi含量都很低,生长过程中未发现对BSi的累积效应,对芦苇和海三棱蔗草在Si素吸收上并不存在竞争。芦苇在生长季内BSi容量最高,其次为互花米草,海三棱蔗草最低。通过估算得出崇明东滩盐沼植物地上部分BSi总储量高达406.18t,仅芦苇就占了53%,对长江口潮滩湿地BSi储量起着巨大贡献。植株体内BSi含量与根际沉积物BSi含量和C/N值之间都存在显著的正相关关系,证明了沉积物影响植物对BSi的吸收累积,而植株体内BSi含量与C/N值存在的显著正相关关系,原因可能在于植株体内高的C/N值可能加速植株体内BSi的富集作用。更多还原

【Abstract】 Silica is an essential element for diatom growth, which is the principal contributor of primary productivity. Biogenic silica is produced in the euphotic zone of the ocean by siliceous plankton such as diatoms, whose accumulation in the sediment can reflect the spatial and temporal distribution of productivity, in addition, the preservation and dissolution of biogenic silica played an important role in influencing the occurrence of eutrophication problems in the coastal zone. Takeing the Yangtze estuarine and coastal ecosystem as an example, this article discussed the temporal and spatial distribution of biogenic silica in the sediments, and the transfer and accumulation effects of biogenic silica had also been analyzed. Meanwhile, the accumulation mechanism of salt marsh vegetation had also been discussed.The main results are as follows:The significant seasonal variations of biogenic silica contents in surface sediments were observed along the coastal zone of the Yangtze Estuary: The biogenic silica contents in the nearshore sediments varied from 0.46% to 1.61% and gradually increased from land to sea in February, while in August they were in the range of 0.39%～1.36% and had the opposite spatial distribution pattern to February; Biogenic silica contents in surface sediments from the shoals varied from 0.47% to 1.02%, and had the similar spatial distribution pattern with the nearshore sediment in February, besides, the significant differences in biogenic silica contents were observed in high, middle and low intertidal flats of different shoals. The relation analysis of the sediment physico-chemical property and biogenic silica announced that biogenic silica contents had close correlation with sediment types and organic matter. In general, biogenic silica was apt to accumulate in the fine fractions of sediments rich in organic matter. Additionally, it was found that benthic diatoms might be an important source of biogenic silica in surface sediments.The biogenic silica buried in the sediment cores were analyzed by a mild acid-mild alkaline sequential extraction method. Results showed that: biogenic silica extracted by mild acid (Si-HCl) was much lower than that extracted by mild alkaline (Si-Alk). Compared to previous study, mild acid pretreatment can markedly increase the biogenic silica content extracted from the core sediment. Sediments with different particle size had different vertical distributions. For example, the Si-HCl and Si-Alk contents in the sediments 125-250μm and 63-125μm gradually decreased with the depth increased, while the sediment with particle size <63μm had the opposite spatial distribution pattern, furthermore, their mean cotents reduced with the particle size decreasing. Under the influence of plant growth, the biogenic silica contents in the 30cm sediments of the high and middle intertidal flats were much higher than that of the low intertidal flat, and the highest contents were all found in August, in which the most biomass obtained. Meanwhile, different variations were found in different month. The relation analysis announced that both of Si-HCl and Si-Alk contents correlated closely with organic carbon and organic nitrogen, suggesting the close relationship between biogenic silica and organic matter during sedimentation process.Strong enrichment of biogenic silica were found in Phragmites astralis and Scirpus mariqueter during their growing seasons, especially for P. astralis reeds in which a linear cumulation was found, and the biogenic silica content reached 4.86% at The end of growing season. However, biogenic silica content in Spartina alterniflora was much lower and no cumulation was found during the growing seasons. As thus, compared to Phragmites astralis and Scirpus mariqueter, S. alterniflora had no competitive ability in silica uptake. In addition, biogenic silica capability of the three plants were also analyzed, result suggested that P. astralis had the highest capability and S. alterniflora takes the second place while S. mariqueter had the lowest capability. The biogenic silica storage of salt marsh plants in Chongming Dongtan was estimated to 406.18t, of which P. astralis accounted for 53%, making magnitude contribution for biogenic silica storage in the intertidal wetland of the Yangtze Estuary. The relation analysis of the biogenic silica and organic nitrogen contents in rhizosphere sediment with biogenic silica contents in plant suggested that sediment effected biogenic silica enrichment in plant, and furthermore, the significant correlation with C/N ratio in plant showed that high C/N ratio may accelerate biogenic silica accumulation in plant.更多还原