上世纪黄河的频繁断流以及大规模的围填海活动导致黄河口湿地出现严重的生态退化，自2002年以来黄河三角洲国家级湿地自然保护区管理局基于小浪底调水调沙工程开始对退化湿地实施淡水恢复工程。淡水恢复在显著降低土壤盐分的同时，明显改变了滨海湿地的营养元素的生物地球化学循环，促进了湿地植被及栖息生境恢复。但是，作为氮限制的滨海湿地生态系统，氮损失将会直接影响湿地生产力，而淡水恢复导致的湿地淹水和土壤盐度的变化是否对湿地土壤硝酸盐异化还原过程产生影响则是当前需要澄清的一个关键科学问题。 反硝化作用、厌氧氨氧化作用（Anammox）和硝酸盐异化还原为氨（DNRA）作用是硝酸盐异化还原过程的三种主要途径。本研究根据淡水恢复工程实施年限，在黄河口选取了2002年恢复区、2006年恢复区和未恢复区三种典型样区，利用泥浆实验结合15N稳定同位素示踪技术，定量分析了各样区土壤或沉积物的反硝化作用潜力、厌氧氨氧化作用潜力和DNRA作用潜力，阐明了研究区域的土壤环境因子对硝酸盐异化还原过程的影响，揭示了盐分的改变对厌氧氨氧化作用和反硝化作用的影响规律。主要研究结果如下： （1）黄河口滨海湿地硝酸盐异化还原过程包括反硝化作用、厌氧氨氧化作用和DNRA作用三个过程；淡水恢复工程对滨海湿地硝酸盐异化还原过程有显著的影响。在2002年恢复区和2006年恢复区，硝酸盐异化还原过程以反硝化作用为主，在削减硝酸盐含量和防止水体富营养化方面发挥着非常重要的作用；在未恢复区，硝酸盐异化还原过程则以厌氧氨氧化作用为主；无论是恢复区湿地还是未恢复区湿地，DNRA作用在硝酸盐异化还原过程中的贡献度均较低。在微生物群落结构中，2002年恢复区和2006年恢复区的反硝化细菌占比要比未恢复区的反硝化细菌占比高得多，而这也是恢复区湿地反硝化作用在硝酸盐异化还原过程中占据绝对优势的生理基础。 （2）盐度和硝酸盐含量是影响反硝化作用的主要土壤环境因子，二者均对反硝化作用产生了抑制作用。影响厌氧氨氧化作用的土壤环境因子则主要包括pH、盐度、有机碳含量和硝态氮含量，除pH对厌氧氨氧化作用呈现抑制作用外，其他因子均呈促进作用。硝态氮含量是影响DNRA作用的关键土壤环境因子，对DNRA作用产生了抑制作用。 （3）单一盐离子或盐度的改变对厌氧氨氧化作用的影响存在不确定性，而盐度和盐离子的交互作用则会对厌氧氨氧化作用产生显著影响。在同一盐离子不同盐度的条件下厌氧氨氧化作用强度并没有表现出明显的规律性而普遍呈现出一种波动的变化趋势，这可能与湿地土壤具有较高的空间异质性有关。不同盐离子（Cl-和SO42-）对厌氧氨氧化作用的影响一般呈现出相反的趋势。 （4）单一盐离子或盐度的改变对反硝化作用的影响也存在不确定性，而盐度和盐离子的交互作用则会对反硝化作用产生显著影响。当Cl-和SO42-浓度发生变化时，两种离子对反硝化作用的影响并不相同。低浓度的Cl-往往会促进反硝化作用，但随着Cl-浓度的增加，反硝化作用则会受到抑制，1ppt是Cl-对研究区沉积物反硝化作用的影响的一个关键拐点。而随着SO42-浓度增加，反硝化作用则呈现出波动下降的趋势。在高盐度水平下，无论是Cl-还是SO42-离子均对反硝化作用产生了明显的抑制作用。

In the last century, frequent river setting off and large-scale reclamation activities resulted in severe ecological degradation of coastal wetlands in the Yellow River Estuary. Since 2002, the Administration Bureau of the Yellow River Delta National Wetland Nature Reserve has started to implement fresh water restoration project to restore degraded coastal wetlands based on the water and sediment regulationproject from Xiaolangdi Reservoir. After the implement of Freshwater restoration project,soil salinity was significantly reduced and thus considerably altered the biogeochemical cycles of nutrients in coastal wetlands, promoting the restoration of wetland vegetation and habitats. However, as a nitrogen-limited coastal wetland ecosystem, nitrogen loss will directly affect wetland productivity. However, whether wetland flooding and changes in soil salinity caused by freshwater restoration will have an impact on the dissimilatorynitrate reduction processes in wetlands is a key scientific issuein need of clarificationcurrently. Denitrification, anaerobic ammonia oxidation (Anammox) and dissimilatory nitrate reduction to ammonium (DNRA) are the three main pathways for dissimilatory nitrate reduction processes. In this study, according to the implementation year of freshwater restoration project, three study areas were selected, including the restorationareasince 2002 (RA2002), the restoration area since 2006 (RA2006), and unrestored area. Mud experiments and 15N stable isotope tracer techniques were used to quantitatively determine the denitrification potential rates, anammox potential rates and DNRA potential rates of soils in each of three sampling areas.The effects of soil environmental factors on the three different processes in each sampling area were also analyzed. Meanwhile, the effects of salt salinity and salt ions on both anammox and denitrification processes were identified. The key research findings were obtained： （1）The dissimilatory nitrate reduction processes include denitrification, anaerobic ammonia oxidation, and DNRA in coastal wetlands of the Yellow River Estuary. The freshwater restoration project showed a significant impact on the dissimilatory nitrate reduction process in coastal wetlands of the Yellow River Estuary. In the RA2002 and RA2006, denitrification was an absolutely dominant dissimilatory nitrate reduction process and played an important role in reducing the active nitrogen levels from the Yellow River and preventing the eutrophication of water bodies. In the unrestored area, the anaerobic ammonia oxidation process became the main process of dissimilatory nitrate reduction.; Generally, DNRA accounted for a lower proportion of the dissimilatory nitrate reduction processes in these freshwater restored or unrestored wetlands. The denitrifying bacteria accounted for much higher percentage in microbial community structure of the restoration area than the unrestored area, and this was the physiological basis of denitrification which had an absolute advantage in the dissimilatory nitrate reduction processes. （2）The soil environmental factors influencing denitrification proceses in three sampling areas mainly included salinity and nitrate content, both of which have inhibitory effects on denitrification. Soil pH, salinity, soil organic carbon, and nitrate were the key soil environmental factors that affected Anammox , and they had a promoting effect on Anammox except for an inhibitory effect of soil pH. Among the soil environmental factors, nitrate considerabally inhibited DNRA processes . （3）The uncertainty effects of salt ions or salinity on Anammox processes could be observed, however, the interaction of salinity and salt ions had a significant effect on a Anammox. The intensity of anaerobic ammonia oxidation showed a fluctuational changes along increasing salinity at different salt ions, which might be associated with the high spatial heterogeneity of wetland soils. The effects of Cl- and SO42- on Anammox tended to show the opposite tendency along increasing salinity levels, indicating that the effect of different salt ions on anammox oxidation was not the same. （4）Similarto Anammox，the effects of salt ions or salinity on denitrification were uncertainly identified, whereas the interaction of salinity and salt ions had a significant effect. The different effects of both salt ions (i.e., Cl- and SO42-) on denitrification were observed. Denitrification was usually promoted firstly at low Cl- levels, and then the inhibitory effects occurred. 1 ppt was an inflection point of the influence of Cl- on the denitrification of wetland soils in the study area. Comparatively,With the increase of, denitrification would show a fluctuation tendency with inceasing SO42- levels. Generally, either Cl- or SO42- had a significant inhibitory effect on denitrification at high salinity ranges.