Removal and Mass Balance of Phosphorus and Silica in the Turbidity Maximum Zone of the Changjiang Estuary

Abstract

The concentration of suspended particulate matter (SPM), sedimentation flux and various forms of phosphorus and silica in turbidity maximum zone (TMZ) in the Changjiang (Yangtze) estuary was studied. Based on the budget of P and Si, their mass balances in the TMZ were calculated. Research results show that the variation in concentration of dissolved inorganic silicon (DISi) was mainly controlled by sea water dilution in the Changjiang estuary, while that of dissolved inorganic phosphorus (DIP) was considerably affected by the buffering of suspended matter and sediment. The sedimentation fluxes of suspended particulate matter and particulate inorganic phosphorus (PIP), total particulate phosphorus (TPP), particulate inorganic silicon (PISi) and biological silicon (BSi) in the TMZ were 238.4 g m−2 d−1 and 28.3, 43.1, 79.0, 63.0 mg m−2 d−1, respectively. In addition, a simple method to estimate the ratio of resuspension of sediment in the TMZ was established, indicating that the sediment resuspension in the TMZ influenced significantly the mass balances of P and Si. Particulate-adsorbed P (60.8%) and 35.5% of TPP discharged from the river were filtered and then deposited in the TMZ. The input flux of PIP from the river mouth was 55.9% of that of DIP, being important as biologically available P, while that of PISi was only 3.5% of DISi, showing that particulate-adsorbed Si was much less important than particulate-adsorbed P.