The impact of extreme precipitation on physical and biogeochemical processes regarding with nutrient dynamics in a semi-closed bay

An extreme precipitation event in August 2012 changed the ecosystem of Jiaozhou Bay (JZB), China. Biochemical variables in the sea, river mouths, and rainwater were monitored simultaneously during the event. The impact of the following excessive riverine input and wet atmospheric deposition on nutrient dynamics were studied before. However, regulatory processes of nutrient dynamics were not quantified and analyzed. Therefore, a coupled physical-biological model (FVCOM-ERSEM) was used to study the physical and biochemical mecha-nisms of the variation of the dissolved inorganic nitrogen (DIN), phosphorus (DIP), and silicon (DISi), as well as chlorophyll-a (Chl-a). The results indicate that physical processes increase nutrients, while biological processes reduce them. The exchange with the Yellow Sea, as an important physical process, exports DIN to the Yellow Sea, but imports DIP and DISi to the JZB. Only 20 % of the excessive DIN due to extreme precipitation event was reduced by water exchange with the Yellow Sea. The rest (80 %) was reduced and changed into organic nitrogen through biological processes. This paper also examines the variation of the pelagic and benthic cycles of biochemical processes. In these cycles, phytoplankton take up and use nutrients in the bay, while zooplankton excretion in the pelagic cycle and benthic releases resupply them. Precipitation enriched the surface nutrients, which boosted primary production and organic matter transport to the bottom water.