Fluctuations and Benthic Flux of Inorganic Nutrients Associated with Tidal Cycles and Its Implications to the Outwelling Process in Garolim Bay, Yellow Sea

To better understand the tidal effects on dynamics of inorganic nutrients and its implications for outwelling processes, we conducted time-series observations on the fluctuations in concentrations and benthic flux of inorganic nutrients with tidal cycle in macrotidal Garolim Bay (GB), Yellow Sea. The strong tidal current and rapid mixing stimulated resuspension of suspended particulate matter (SPM), particulate organic carbon (POC), and chlorophyll-a (Chl-a), which were predominant during the spring tide. Concentrations of ammonium (NH₄⁺) and NO_x (sum of nitrite and nitrate) were not correlated with tidal variation, while concentrations of phosphate (PO₄³⁻) and silicate (SiO₂) were inversely correlated with tidal levels, except for PO₄³⁻ at surface layer during neap tide. In addition, analyses of the benthic nutrient fluxes (0.04–3.48 mmol m⁻² d⁻¹ for NH₄⁺, 0.18–0.39 mmol m⁻² d⁻¹ for NO_x, 0.03–0.12 mmol m⁻² d⁻¹ for PO₄³⁻, and 1.62–5.47 mmol m⁻² d⁻¹ for SiO₂) and nutrient ratio revealed that there was a relatively excess efflux of PO₄³⁻ and SiO₂. The inverse fluctuations of P and Si with tidal level and their excess benthic release indicated that GB sediment acts as a net source of PO₄³⁻ and SiO₂ to the water column and to offshore water, which further suggested that the benthic nutrient flux in the GB may have a substantial effect on phytoplankton production in the adjacent coastal water column.