10 / 2024-07-30 11:13:46

The Roles of Nutrient Loading and River Discharge on the Phytoplankton Dynamics in the Semi-enclosed Sea

ecolocial modelling,nutrient dynamics,phytoplankton dynamics

Understanding spatiotemporal variations in phytoplankton biomass is crucial to the health of marine ecosystems. Therefore, the Finite Volume Community Ocean Model (FVCOM)-based Ecolgocial Model (Integrated Compartment Model) was implemented to assess interannual nutrient and phytoplankton dynamics in the Bohai Sea from 2010 to 2019. From 2010 to 2013, dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) levels in the Bohai Sea were higher (~0.400 and 0.030 mg/L, respectively) in nearshore areas compared to other years. During the summer and fall, the spatial distribution of the DIN/DIP ratio in the Bohai Sea exhibited a double-core structure. Higher values (>100) were primarily concentrated in the central region of the Liaodong Bay and south of the central basin near the Yellow River Estuary. Statistical analyses and numerical experiments revealed that adjusting DIP loading had a greater effect on phytoplankton biomass in the Laizhou and Bohai Bays than adjusting DIN loading. However, the phytoplankton biomass in the Liaodong Bay was strongly influenced by both DIN and DIP loading adjustments. Notably, the increase in phytoplankton biomass resulting from adjusting DIN loading exceeded that from adjusting DIP loading by 55% in the Liaodong Bay. The reduction in river discharge weakened circulation at the river mouths, thereby partially retaining surface phytoplankton. This was more predominant in the nearshore areas of the Yellow and Liao Rivers owing to the higher river discharge in August 2019.