A simulation of the seasonal variation of decabromodiphenyl ether in a bay adjacent to the Yellow Sea

Abstract A three-dimensional transport-ecosystem-POP coupled model is configured to simulate the seasonal variation and budget of decabromodiphenyl ether (BDE-209) in a semi-enclosed bay adjacent to the Yellow Sea. The model includes five types of BDE-209 (gaseous, dissolved, phytoplankton-bound, detritus-bound, and suspended particulate matter (SPM)-bound) and related physical and biogeochemical processes, such as advection and diffusion due to seawater motion, input from rivers, air-sea exchange, decomposition of dissolved BDE-209, uptake and depuration between dissolved and phytoplankton-bound BDE-209, mortality of phytoplankton-bound BDE-209, remineralization and sinking of detritus-bound BDE-209, and sinking of SPM-bound BDE-209. Model results show that the dissolved and particulate BDE-209 in the bay are higher in the nearshore area than in offshore area and are higher in summer than in other seasons; these results are consistent with field data. SPM-bound BDE-209 is dominant among the five types due to its large supplying from rivers. Dissolved BDE-209 concentrations are around 5-fold that of phytoplankton-bound BDE-209, which depends on uptake and depuration rate constants between dissolved and phytoplankton-bound BDE-209 and biomass of phytoplankton. Evaluation of mass balance indicates that the input from rivers is major source of BDE-209, while the exchange with the Yellow Sea is major sink. Sensitivity experiments demonstrate that the input of BDE-209 from rivers plays the most significant role in the seasonal variation of dissolved and particulate BDE-209 concentrations, and the change in water temperature is a secondary factor.