长江口潮滩湿地生源要素氮的生物地球化学过程研究

【作者】 侯立军；

【导师】 陆健健；

【作者基本信息】 华东师范大学 ， 生物学， 2006， 博士

【摘要】 河口滨岸潮滩是陆地、海洋和大气之间各种过程相互作用最为活跃的界面，是地球系统中最富有生机的多功能生态系统之一，具有独特的生态价值和资源潜力，对人类的生存和经济发展起着十分重要的作用。同时，受陆海相互作用影响，河口滨岸潮滩地区各种物理、化学、生物因素变化十分剧烈，具有波潮径流水动力作用强烈、物质交换频繁、物理化学要素变化梯度大等环境特征，是一个典型的环境脆弱带，对于各种自然过程变化引起的波动和人类活动的影响反应十分敏感。随着人口的不断增长和经济的飞速发展，大量污染物输入到河口滨岸地区，给水体环境质量造成了不同程度的威胁，对潮滩环境的初级生产力、生物多样性以及滨岸生态系统结构与功能等产生深刻的负面效应。其中，由营养盐过量输入与累积而引起的水体富营养化（赤潮）对河口滨岸潮滩生态环境产生的潜在影响与危害，早在二十世纪六、七十年代就引起了人们的广泛关注，当前该环境问题已经成为国际海岸带研究的热点和重点之一。 氮是影响河口及其近岸生态系统富营养化发生和演变的关键生源要素之一，目前，人为氮输入已经大大超过了它的天然输入，这些高负荷的氮素绝大多数滞留于河口与近岸地带。因而，由氮素过量输入与富集而引发的河口及近岸水体富营养化是当今面临的一个全球性重大环境问题。河口滨岸潮滩作为营养盐氮的主要源、汇和转换器之一，在河口营养状况的控制以及河口氮循环过程中扮演着十分重要的角色，但是目前有关氮素在河口滨岸潮滩这一复杂环境系统内的迁移转化过程及其影响机制尚缺乏深入研究。鉴于此，以长江口作为典型研究区域，探讨了河口滨岸潮滩氮素生物地球化学循环中的关键过程，并取得了以下主要认识和研究成果：（1）利用潮滩沉积物-水界面间无机氮的浓度梯度，并依据Fick’s第一定律对无机氮的界面迁移扩散与沉积物的源-汇效应进行了研究和探讨。结果表明，氨氮（NH₄⁺-N）扩散通量的时空分布比较复杂，孔隙水中NH₄⁺-N的再生过程是控制其界面扩散通量的主要因素。在潮滩环境系统内，NH₄⁺-N的界面扩散以负通量为主，即NH₄⁺-N主要由沉积物向上覆水中扩散，反映了沉积物是上覆水中NH₄⁺-N的重要来源之一。对硝态氮（NO₃^--N）而言，其界面扩散以正通量为主，即NO₃^--N主要自上覆水向沉积物中扩散，说明沉积物是上覆水中NO₃^--N的重要蓄积库（汇），对削减上覆水中高含量的NO₃^--N具有重要的环境意义。NO₃^--N界面扩散通量的空间分布显示，在浒浦至石洞口采样岸段，NO₃^--N的界面扩散通量较小，而在吴淞口至芦潮港采样岸段，NO₃^--N的界面扩散通量普遍较高，并且研究发现上覆水与孔隙水之间的NO₃^--N浓度梯度是控制NO₃^--N界面扩散时空变化差异的主要因素。（2）基丁长江口岸带潮滩沉积环境的分异特征，选择东海农场站位作为典型的野外现场监测点，并依据潮滩暴露期间沉积物中氨氮的变化量，对沉积物中氨氮的再生过程进行了分析和探讨。研究发现，在潮滩暴露期间沉积物中吸附态氨氮含量呈现明显的增加趋势，而溶解态氨氮含量变化相对比较复杂。根据潮滩暴露过程中氨氮的累积量，计算了沉积物中氨氮的再生速率，估算结果表明潮滩表层沉积物中氨氮具有较快的再生过程，再生速率约为496.89更多还原

【Abstract】 The estuarine and coastal tidal flat, as a typical transitional zone between land and ocean, is a multifunctional and complex ecosystem with special ecological values and potential resources. Due to the interaction between land and ocean, the estuarine and coastal tidal flat is characterized by intense hydrodynamic conditions, frequent sediment transport and material exchange, steep physiochemical gradients and high biodiversity. With population’s growth and economic development, lots of contaminants transported into estuarine and coastal zones have the negative influence on tidal water quality and the structures and functions of coastal ecosystem. Especially, more and more concerns have been focused on coastal eutrophication induced by the excessive input of nutrients.Nitrogen is one of key nutrient elements that result in the eutrophication and evolvement of estuarine and coastal ecosystems. Recently, anthropogenic input of nitrogen has already exceeded its natural origin in the estuarine and coastal regions, and furthermore the high loading of nitrogen is mainly retained in the areas. The coastal and tidal flats as important sources and sinks of nitrogen play key roles in nitrogen cycling in estuarine systems. However, the biogeochemical processes of nitrogen and their mechanisms in the complex systems remains unclear. Therefore, we chose the Yangtze estuary as a typical study area, and further studied the key processes of nitrogen cycling. The main findings are as following: （1） The magnitudes of the benthic exchange fluxes were determined on the basis of concentration gradients of ammonium and nitrate at the near-bottom water and interstitial water interface in combination with calculations of a modified Fick’s first law. Ammonium fluxes varied from -5.05 to 1.43μg N cm^-2 d^-1 and were greatly regulated by the production of ammonium in surface sediments, while nitrate fluxes ranged from -0.38 to 1.36 ug N cm^-2 d^-1 and maybe were controlled by the changes in nitrate concentration gradients at the sediment-water interface. It was found that ammonium was mainly released from sediments into water columns at most of stations whereas nitrate was mostly diffused from overlying waters to intertidal sediments. In total, c. 823.75 t ammonium-N yr^-1 was passed from intertidal sediments to water while about 521.90 t nitrate-N yr^-1 was removed from overlying waters to intertidal sediments. This suggests that intertidal sediments had the significant influence on modulating inorganic nitrogen in tidal waters. （2） The influences of exposure to atmosphere on ammonium cycle in the intertidal surface sediments were in situ studied with a geochemical approach更多还原