Nitrogen pollution is one of the most critical ecological and environmental issues on the earth's ecological system, which has attracted consideration attentions globally. Nitrogen pollution in estuarine and coastal zones has caused a series of ecological and environmental problems, such as water eutrophication, biodiversity reduction, and ecological degradation, as well as the greenhouse gas emissions. These environmental problems have seriously restricted the high-quality and sustainable development of estuarine and coastal zones. Therefore, the nitrogen cycle in estuarine and coastal zones is not only a frontier and hot spot in the geoscience research, but also a major scientific and technological demand for environmental protection, ecological restoration and management of estuarine and coastal areas as well as high-quality development. We studied the nitrogen cycle in estuarine and coastal zones, the results indicated that denitrification and dissimilation nitrate reduction to ammonium showed significant zonal differentiation, which were controlled by mean annual temperature. However, there was no zonal difference in latitude of anammox, which was mainly affected by sediment characteristics. During the nitrogen cycling, N₂O, a strong greenhouse gas, was produced, and the release fluxes were observed to increase with the increasing human activities intensities. The N₂O showed a sink in spring and a source in other seasons. At the same time, N₂O emission with tidal variation presented a periodic change characteristic of sink during high tide and source at low tide. At the same time, enhanced nitrogen loading, global warming and acidification altered the pathways of N₂O production, and further changed the fluxes. The greenhouse effect of N₂O emossions from estuarine and coastal wetlands can offset 4–7% of climate effect of wetland carbon sink. Therefore, estuaries and coasts are important sources of N₂O emissions, which has a positive feedback to climate change, and the model prediction should be strengthened.

nitrogen cycling; estuaries and coasts; human activity; global change