Natural and anthropogenic effects on the primary production in Gwanyang Bay, Korea.

Coasts are undergoing various environmental changes due to human activities and natural variability. However, it is difficult to identify what causes mainly environmental change due to complex effects. The environment of Gwangyang Bay, which is downstream of the Sumjin River, is greatly affected by the variation of river discharge. Over the last few decades, Gwangyang Bay has experienced numerous anthropogenic environmental changes, including industrial development, dam construction, and sewage treatment plant construction. According to the results of long-term observation in Gwangyang Bay, the concentration of chlorophyll in February and August has decreased significantly since 2016. Previous studies reported that phytoplankton biomass changes due to various causes such as light, temperature, nutrients, inhibition/strengthening of the trophic chain reaction, and changes in dominant species. Managing terrestrial nutrient loads may affect the phytoplankton biomass. Changes in turbidity and water temperature may also affect phytoplankton photosynthesis, possibly affecting the succession of dominant species. This study aims to understand the effect of long-term changes in light, temperature, and nutrient variation by human activities and natural variability in Gwangyang Bay, on primary production. The ROMS-Fennel model was used in this study to quantify the impact of anthropogenic environmental changes and natural variability on primary production in Gwangyang Bay.