长江口夏季缺氧区氧化亚氮调控机制研究

Nitrous oxide (N2O) is an important greenhouse gas, and plays a significant role in the global climate system. Marine waters, in particular the coastal aquatic systems are the major regimes of N2O production, and thus represent an important component of the marine nitrogen cycle. Quantification of marine N2O emissions and the associated key processes in the marine systems have been a hot and challenging topic of ocean biogeochemistry study. We observed anoxia in the summer bottom water of Yangtze River Estuary, and the N2O and nitrate were reduced to 0. A hypothesis is put forward: denitrification would be major control of N2O production and consumption in the increasing hypoxia water of the Yangtze River Estuary. This project is to examine temporal and spatial variations of N2O in the hypoxia zone of Yangtze River Estuary, which is heavily impacted by human activities. The stable nitrogen isotopic composition of N2O will also be investigated. In addition, the diversity and abundance of microorganisms and functional genes are to be explored. Then, the mechanism of N2O production and consumption in the hypoxia water of the Yangtze River Estuary will be comprehensively discussed. In generally, this proposal will help to deepen the understanding of N2O regulation mechanism and nitrogen cycle. It also could provide the scientific basis for the future environmental issue management of the Yangtze River Estuary.

氧化亚氮(N2O)是主要的温室气体之一，还对臭氧层具有破坏作用。海洋是大气N2O的重要释放源，该释放源在河口近岸海域更为显著。准确定量河口近岸海−气N2O通量并掌握其动态变化及其控制过程是海洋学热点科学问题。根据我们在长江口夏季观测到的底层水体出现无氧以及N2O浓度接近于零的现象，本研究提出假设：长江口底层水体由缺氧演化至无氧过程中，水体N2O主要调控机制由硝化作用向反硝化作用转化。本项目选择受人为活动干扰作用强烈的长江口缺氧区进行研究，从N2O、溶解氧、营养盐等理化参数时空分布规律入手，结合稳定同位素，微生物和功能基因多样性，有望揭示长江口缺氧区N2O的动态分布，定量评估海−气N2O交换通量，探讨长江口缺氧加剧下N2O关键影响因素和调控机制，研究硝化与反硝化过程对N2O产生和消耗的作用，从过程机理上增强海洋氮循环的认识，为寻求长江口富营养化及缺氧现象等环境问题的治理提供科学依据。

大气圈的氧化亚氮(N2O)既是主要的温室气体之一，也对臭氧层具有破坏作用。海洋是大气N2O的重要来源，在近岸河口海域更为显著。本项目瞄准国际关注的河口缺氧和氮循环热点领域，针对海洋N2O产生和释放科学问题，选择人类活动干扰强烈的河口-长江口缺氧区进行研究。项目执行期间，开展了4个长江口调查航次调查，从N2O时空分布规律入手，结合溶解氧、营养盐等理化参数，初步揭示长江口N2O的时空分布特征，定量评估海−气N2O通量。研究表明，在强厄尔尼若（El Niño）受影响的年份，长江口夏季底层水体缺氧形成、加剧，并演化至无氧状态的过程中，水体N2O主要调控机制由硝化作用向反硝化作用转化，并最终被消耗，并由N2O源向N2O汇的新格局转化。本项目探讨了长江口缺氧加剧下N2O关键影响因素和调控机制，加深对河口缺氧区N2O形成和释放过程的认识，同时也为环境保护部门制定相关政策提供科学依据。