Tracing atmospheric nitrogen deposition and its impact on Hong Kong and Chinese coastal ecosystem

Nitrogen deposition plays an important role in both air and water quality. Nitrogen emissions in cities increase are high due mainly due to transportation and industrial activities and predicted to further increase. As nitrogen is often the limiting nutrient in coastal waters, the excess nitrogen deposition may enhance the phytoplankton growth, resulting in eutrophication leading to a cascade of ecological impacts. Thus, understanding the nitrogen sources and its potential impacts are crucial to mitigate the nitrogen pollution in coastal waters. In this thesis, I used multi stable isotope analysis of wet and dry deposition in Hong Kong to identify the atmospheric sources of nitrogen and the seasonal trend. I characterized the δ15N values of wet deposition, which is useful for further analysis of the nitrate sources in seawater. Next, I examined the ecological impact of future trend of nitrogen deposition in China. Specially, I used a biogeochemical model to estimate the future hypoxia area of such deposition, suggesting that reducing nitrogen deposition can reduce the hypoxia area. Moreover, it indicates that nitrogen deposition will potentially affect the hypoxia area if we do not regulate emissions in the future. This thesis provides a new approach to study the trend and impact of nitrogen deposition, which will allow more understanding on its significance to the coastal ecosystem. <br><br>The dataset composed of the dual isotopes analysis of dry and wet deposition, bulk isotopes analysis of dry deposition and ammonia data of dry and wet deposition.<br>

氮沉降对空气质量与水环境质量均具有显著影响。城市氮排放量长期居高不下，主要源自交通与工业活动，且预计未来仍将持续攀升。由于氮素往往是近岸海域的限制性营养盐，过量氮沉降会刺激浮游植物异常增殖，进而引发水体富营养化，最终诱发一系列连锁生态效应。因此，厘清氮沉降的来源及其潜在生态影响，对于防控近岸海域氮污染至关重要。本研究以香港地区为研究区域，通过对干湿沉降开展多稳定同位素分析，解析了氮素的大气来源及其季节变化特征；测定了湿沉降的δ¹⁵N（δ15N）比值，该数据可为后续海水硝酸盐的来源解析提供重要支撑。随后，本研究进一步探讨了我国未来氮沉降趋势的生态影响：具体而言，通过构建生物地球化学模型，估算了该类沉降驱动的未来低氧区面积，结果显示削减氮沉降可有效缩减低氧区规模。此外，研究结果还表明，若未来不实施排放管控措施，氮沉降将对近岸海域低氧区面积产生潜在影响。本研究提出了一种研究氮沉降趋势与影响的新方法，有助于更全面地理解其对近岸生态系统的重要意义。

本数据集涵盖干湿沉降的双同位素分析数据、干沉降的总量同位素分析数据，以及干湿沉降的氨浓度监测数据。