渤海氮循环的关键过程与调控机制

The Bohai Sea has been known for being an important commercial fish habitat and sea farm base in Chinese coastal seas, however, recently the Bohai ecological environment has changed, which restricted the sustainability of Bohai Sea ecosystem. The proposed study, based on applicant and her research group’s studies on biogeochemistry of nutrients in the Huanghe estuary and the Bohai Sea in the last more than 20 years, starts at the intersection between physical oceanography, biogeochemical and marine biology. We will use stable isotope tracer techniques to quantify the rates of key nitrogen transformation processes (nitrification, denitrification, anaerobic oxidation of ammonium, dissimilatory nitrate reduction to ammonium etc.) and their spatial and temporal variations in the Bohai Sea, and try to understand dynamics of produced N2O during nitrogen cycle. We address factors affecting the temporal and spatial variations of oxygen consumption rate and nutrient regeneration rates at the sediment and overlying water interface in the Bohai Sea, and to understand the coupling of water column and sediments. By analyzing natural stable isotopic composition of various nitrogen species in water column and sediment pore waters of the Bohai Sea, field observations and incubation experiments, and numerical simulation, we address factors affecting key nitrogen transformation processes and the effects of nitrogen cycle on nutrient composition in the Bohai Sea interfered by intensive human activities. Its successful implementation should have strong scientific basis to the protection of the Bohai Sea ecological environment.

渤海是我国重要的经济鱼类栖息地和海水养殖基地，然而近年来渤海的生态环境发生了明显改变，制约了渤海生态系统的可持续发展。本项目以申请人及其团队20多年来在黄河口和渤海开展的生源要素海洋生物地球化学研究为基础，拟从物理海洋学、生物地球化学和海洋生物学之间的交叉点出发，利用稳定氮同位素示踪技术，量化渤海氮循环的关键过程—硝化、反硝化、缺氧铵氧化和硝酸盐异化还原为铵等的速率及其季节分布特征，认识氮循环关键过程引起温室气体N2O产生量的动态变化；分析沉积物-水界面间的耗氧速率以及营养盐再生速率的分布变化特征及其主要控制因子，探讨氮在水层与沉积物中的耦合作用；结合分析水体与沉积物间隙水中不同氮组分的天然稳定氮同位素组成、现场观测与受控实验结果、数值模拟，认识高强度人类活动干扰下渤海氮循环的关键过程及其调控机制，氮循环引起的营养盐组成和结构的变化。为渤海生态环境保护与资源的合理开发提供科学支撑。

实施了渤海9个航次的出海调查，并采集了河流与大气沉降样品。分析了营养盐与N2O的动态变化及与生物和物理过程的耦合作用，研究了沉积物耗氧速率与沉积物-水界面营养盐及N2O的交换速率，研究了沉积物与水体中关键氮转化过程变化特征及其调控机制。分析了浮游植物丰度与组成、水体和沉积物中氮循环和总微生物的丰度与多样性，结合数值模型综合分析了氮循环的变化特征，以及对营养盐组成和结构的影响。项目已发表研究论文30篇，其中SCI论文20篇，培养博士后和毕业研究生共计12名。取得的主要认识有：.1 渤海沉积物－水界面氮的再生与氮循环的关键过程. 利用自行组装的膜进样质谱系统改进了加富样品中15NH4+和15NO3-的测定方法。沉积物耗氧速率时空变化显著。量化了沉积物-水界面氮营养盐交换通量的时空变化，沉积物中实际的总氮气移除和反硝化速率呈显著的季节变化，厌氧铵氧化在冬季表现较低、其他季节变化不大，异化硝酸盐还原为铵(DNRA)速率普遍较低，硝化速率较高。存在时空变化特征显著的潜在反硝化、厌氧铵氧化和DNRA，脱氮以反硝化为主、厌氧铵氧化仅占13%。相应地，沉积物中反硝化菌的丰度最高，氨氧化细菌和厌氧铵氧化菌次之，氨氧化古菌的丰度最低。氨氧化反应主要由氨氧化细菌所介导。.2 渤海水体中氮的组成与转化过程. 水体中营养盐的消耗与累积，以及浮游植物生长的营养盐限制均呈现季节性和区域性变化。在层化期湍流卷挟是真光层营养盐的重要补充渠道。NO3-变化受同化吸收、硝化作用等的影响。硝化过程主要由氨氧化细菌介导。渤海溶解N2O浓度有明显的季节与区域变化，是大气N2O的源，沉积物是水体N2O的弱汇。.3 渤海水动力与生态耦合模型构建与综合分析. 基于高分辨率渤海环流模型和水层-底栖生态模型的构建，模拟研究了黄河冲淡水的脱离与扩展，评估了渤海海峡的水与营养盐交换通量，厘清了渤海中部营养盐浓度与N/P比值时间变化的影响因素，分析了沉积物中氮的再生与转化过程的季节变化。