Impact of atmospheric nitrogen deposition on phytoplankton productivity in the South China Sea

Abstract

Perturbation in nitrogen (N) cycles is a challenge that mankind faces to keep the environment sustainable. One of accompanying problems is anthropogenic nitrogen deposition to the ocean which has yet to been well recognized until recently. The South China Sea (SCS) surrounded by fast-growing and populated countries is confronting such a problem. In this study, we estimated atmospheric N deposition to the SCS based on 10-years long observation data of the EANET (Acid deposition monitoring network in East Asia) and found it reached ~20% of new production. Furthermore, using a receptor model (concentration weighted trajectory) with the MODIS aqua Chl-a product and HYSPLIT air mass back-trajectory model output, we tried to find upwind areas associated with enhanced chlorophyll-a concentration in the SCS to identify source regions providing anthropogenic N for ocean waters and thus increasing phytoplankton productivity. The results revealed that highly populated areas including the east coasts of China and Indonesia were associated with elevated Chl-a, indicating atmospheric transport of N pollutants from these polluted areas and subsequent deposition to the SCS were responsible for the enhanced Chl-a.The South China Sea (SCS) surrounded by fast-growing and populated countries is confronting such a problem. In this study, we estimated atmospheric N deposition to the SCS based on 10-years long observation data of the EANET (Acid deposition monitoring network in East Asia) and found it reached ~20% of new production. Furthermore, using a receptor model (concentration weighted trajectory) with the MODIS aqua Chl-a product and HYSPLIT air mass back-trajectory model output, we tried to find upwind areas associated with enhanced chlorophyll-a concentration in the SCS to identify source regions providing anthropogenic N for ocean waters and thus increasing phytoplankton productivity. The results revealed that highly populated areas including the east coasts of China and Indonesia were associated with elevated Chl-a, indicating atmospheric transport of N pollutants from these polluted areas and subsequent deposition to the SCS were responsible for the enhanced Chl-a.