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

Abstract

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 NOx (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 NOx, 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.