Program     Ocean Circulation, Ecosystem and Hypoxia around Hong Kong Waters       Poster The role of atmospheric deposition in the generation of eutrophication, hypoxia and harmful algal bloom in Hong Kong P-SPS4-05-S Yau Yu Yan Yvonne* , Department of Earth Sciences and SWIRE Institute for Marine Science, The University of Hong Kong Naomi Geeraert, School of Biological Sciences and SWIRE Institute for Marine Science, The University of Hong Kong David M Baker, School of Biological Sciences and SWIRE Institute for Marine Science, The University of Hong Kong Benoit Thibodeau, Department of Earth Sciences and SWIRE Institute for Marine Science, The University of Hong Kong Presenter Email: u3511209@connect.hku.hk Humans have significantly altered the global nitrogen cycle by artificially fixing N2 in the last century. Anthropogenic creation of reactive nitrogen (N) from fossil fuel combustion and fertilizer production increased ten-fold between 1860 and 2000. A large part of this N is released to the atmosphere, transported over short to large distance and deposited over coastal and marine areas. This new bioavailable N from the atmosphere can act as a fertilizer to the ocean, enhancing primary productivity and biological oxygen demand, which pose many ecological threats such as eutrophication, hypoxia and harmful algal bloom. Waters surrounding Hong Kong suffer from all these problems but the role of atmospheric deposition in this region is still unquantified. It is thus critical to quantify the atmospheric N input and diagnose the sources of pollution in Hong Kong. In this study, we measured δ15N and δ18O of nitrate in the atmospheric N deposition (wet and dry deposition and aerosols) in the Hong Kong. The samples are collected in HKU building, which is surrounded by a mix of commercial and residential area, with intense traffic. Based on the data set, we hope to identify the sources of atmospheric N and quantifying their importance for the marine N budget.