黄河内蒙古段沉积物-水界面间氮磷迁移转化与响应机制研究

The nitrogen and phosphorus cycle was the central content of global biogeochemical and important component of global change study. The distribution, source, converge conversion as well as geochemical cycle process of nitrogen and phosphorus in water ecosystem directly affected the primary productivity of water, then the global carbon cycle, even the global climate change. In this work, Yellow River basins of Inner Mongolia is chosen as experiment area and methods of in situ monitoring, laboratory studies and numerical simulation will be used. The content and distribution of nitrogen and phosphorus will be investigated. The adsorption/desorption character will be studied by means of isothermal adsortion experiments. According to the experimental data, the flux of nitrogen and phosphorus on sediment-water interface will be calculated by ENC0 and EPC0. The nitrogen and phosphorus cycle process will be analysed and the driving factors of water environment, sediment, climate and microbe will be discussed. Culture organism and molecular biotechnology will be used to elucidate the mechanism of driving effect of microbe on the basis of molecular ecology of phosphate solubilizing bacteria, nitrobacteria and denitrifying bacteria, combined with sediment factors(mineral composition, organic carben,et al). The implementation of this project will be beneficial to make realistic assessment of sediment on the function of source and converge as well as the contribution to nitrogen and phosphorus cycle. Moreover, the research will not only provide scientific basis for water resources protection and sustainable development of heavily silt-carrying river, but also to lay the scientific foundation for the estimation the total of nitrogen and phosphorus cycle.

氮磷循环是全球生物地球化学研究的核心内容。水域生态系统中氮磷的分布和含量、源汇转化及其地球化学循环过程直接影响水体的初级生产力，进而影响全球碳循环乃至全球气候变化。本研究以黄河内蒙古段流域为实验区域，通过原位采样监测、实验室研究与数值模拟相结合的方法，测定氮磷的分布和含量，通过等温吸附实验研究其在沉积物-水界面间的吸附/解吸行为，应用临界氮(磷)平衡浓度(EN(P)C0)计算氮磷通量，分析氮磷迁移过程，揭示水环境、沉积物、气候、生物等因素的驱动作用。应用培养实验和分子生物学技术，基于解磷细菌、硝化菌、反硝化菌的分子生态学角度，结合沉积物因素(矿物组成、有机碳含量等)，阐明沉积物特性和微生物对氮磷迁移过程的驱动作用及机制。本项目的实施有助于客观评价黄河内蒙古段沉积物对氮磷的源汇功能及对氮磷循环的贡献，为多沙河流水资源保护及环境的可持续发展提供科学依据，也为准确估算氮磷循环的总量奠定科学基础。

以黄河内蒙古段流域为研究区域，选取乌海、临河、前旗、包头、托县、老牛湾六个采样点，按春、夏、秋三个季节进行六次采样，用便携式水质监测仪监测水质状况。对沉积物中氮磷形态的分布及迁移转化特征、影响因素、微生物机理进行研究。重要结果如下：在黄河沉积物七种磷形态中，原生碎屑磷和钙结合态磷是沉积物磷的主要赋存形态，其含量范围分别为262.36 - 962.56 mg·kg-1和36.32-405.89 mg·kg-1，二者共占总磷含量约74.37%；沉积物对磷的等温吸附特征符合经典的Langmuir吸附模型，对实验数据进行拟合，得到最大吸附容量和吸附平衡常数，最大吸附容量与沉积物中总有机碳，吸附平衡常数与活性铁和铝氧化物的含量有良好线性关系，说明沉积物中有机碳和活性铁、铝是对磷持留的主要物质。通过临界磷平衡浓度值可以判断老牛湾、前旗沉积物表现为磷“汇”，其余四个沉积物表现为磷“源”；在微生物实验中，新鲜沉积物样品中解磷菌数量很小，通过解磷菌培养实验发现各形态磷的含量会发生变化，说明解磷菌在磷的迁移转化过程中发挥一定作用。. 沉积物中四种形态的可转化态氮含量的平均值大小依次为：有机态与硫化物结合态氮（95.35 mg·kg-1）> 铁锰氧化态氮（29.36 mg·kg-1）>离子交换态氮（15.40 mg·kg-1）> 碳酸盐结合态氮（4.24 mg·kg-1）。从季节变化来看，秋季的可转化态氮含量最高，其次是春季、夏季。各可转化态氮含量与总氮含量、有机质、阳离子交换量有不同程度的相关性。对氨氮而言，无论春季、夏季还是秋季，沉积物均充当“氮源”角色；沉积物对硝态氮的吸附符合Langmuir吸附等温模型，拟合得出最大吸附量的范围为75.75 mg·kg-1-98.32 mg·kg-1，夏季>秋季>春季。最大吸附量与沉积物中硝化细菌的含量成正相关，其数量及活性会影响沉积物-水界面氮的迁移与转化，沉积物均充当“氮汇”角色。黄河表层沉积物中总细菌与各形态可转化态氮之间均正相关。总细菌含量随着沉积物有机质含量增多而增多。反硝化细菌总数比硝化细菌多，为优势菌种，反硝化作用占优势。