东海海岸带沉积物脱氮过程及其在有氧-无氧环境中的发生机制

Due to intensive human activities, the current global nitrogen(N) inputs into the coastal region, mainly through the riverine and underground water discharges, have increased 2-4 times more than those in preindustrial period. The majority of those imported nitrogen was removed via two N-loss processes- denitrification and anammox at the coatal region, to maintain the N-balance in oceans. The catchments at coastal region of East China with high density of population and intensive huamn activities, are the core area of economical development in our country, especially the catchments around Yangtze estuary. The annual ammonia-N-input from Chongming Island into Yangtze estuary has approached to 3.2 kilotons.How substantially would the anthropogenic N-inputs be removed by coastal sediments before reaching the water body of Esat China Sea? How about the individual contributions via denitrification and anammox? How about the impacts on the N-loss processes by the environmental limiting factors? So far, little was known. The aim of this research is to not only determine the N-removal pathways and the potential N-loss rates in these coastal sediments by using isotpe paring technique (IPT), but explain their mechanism of N-loss processes combined with the investigation of the organic matter, dissolved oxygen and dissolved inorganic N-contained nutrients in the field. Therefore, this research on N-loss processes in the oxix-anoxic zone at coastal sediments may provide the explicitation on their significance in the current coastal N-cycle.

由于日益加剧的人类活动，全球通过河流和地下水输入而进入海岸带的氮量比非工业化时期增加了2-4倍。海岸带沉积物通过反硝化或厌氧氨氧化这两个氮流失途径，移除了其中绝大部分，基本维持着海洋氮循环的平衡。我国东部沿海，人口密集，人类活动干扰程度强，尤其是长江三角洲区域，每年仅从崇明岛排放到长江口的氨氮量就已达到3.2千吨/年。这些大量人为排放的氮在进入东海开放海域之前有多少通过海岸带沉积物脱氮作用被移除？其各脱氮过程即反硝化和厌氧氨氧化的贡献如何？其在环境因素诱导下发生机制如何?迄今为止，这些问题还没有明确答案。本研究希望利用同位素对技术定量说明东海海岸带沉积物脱氮过程模式；结合对有机质、溶解氧和溶解无机氮的现场研究，探讨该沉积物在氧化-还原环境下的脱氮过程特征与发生机制，阐明东海潮滩沉积物氮流失在现代海岸带氮循环中的重要性。

我国东部沿海面临着人类活动带来的巨大环境压力，长江的氮输入量近二十年增加了7倍之多，海岸带沉积物作为陆地和开放海域的过渡地带，在海岸带氮循环过程中通过脱氮过程调控人为排放氮源向外海输出的作用模式和机制是我们研究的重点，本项目利用同位素对技术定量说明东海海岸带沉积物脱氮过程模式，并结合对溶解氧、溶解无机氮(DIN)和有机质(OM)的现场研究，探讨该沉积物在氧化-还原环境下的脱氮过程特征与发生的环境机制。研究表明，在东海海岸带沉积物的总脱氮速率在170-500μmol N m–2 h–1，厌氧氨氧化贡献占10-25%， 主要仍以反硝化过程贡献为主；以崇明潮滩沉积物脱氮速率研究为例，利用同位素对技术对完整柱芯培养的速率测定结果与对溶解无机氮潮汐时间序列现场研究所获得硝酸盐消耗速率（90-200μmol N m–2 h–1）基本一致，表明原位条件下沉积物可以通过潮汐驱动的沉积物-水体物质交换来持续利用水体中的硝酸盐维持较高的脱氮速率；根据沉积物中氧气实际分布情况对沉积物分层进行的沉积物-水混合物培养实验结果表明在外界硝酸盐充足的条件下，不同层位沉积物脱氮速率高达5-30 mmol N m-3 sedi h-1，并未受到培养环境中氧气的抑制，而是与该层位沉积物的有机质含量呈现一定的相关性。通过以上研究数据和结果的获取，为东海潮滩沉积物的脱氮过程与速率提供了基础数据，为评估该区域氮流失的定量估算提供理论参考数据；并结合原位环境参数分析，初步揭示了该海区沉积物脱氮过程与环境因素之间的关系，为阐明脱氮过程在有氧-无氧环境下的响应机制提供了基础认识。