Dynamic Mechanism Of Sediment Resuspension And Its Ecological Effects On Polyculture Of Shellfish & Macroalgae In Shallow Sea

As a universal physical phenomenon, sediment resuspension plays an important role on the biogeochemical cycle of contamination. In this paper, the area in focus is Sungo Bay, one of the most large-scale aquaculture areas in North China. From the view of physical, chemical and biologic, mechanism of sediment resuspension and its ecological effect is studied; Moreover, the wave-current coupling model and prediction model of suspended sediment concentration is built. Results are as follows:1)The dynamic ratio of Sungo Bay is 1.54, which means this area has the potential dynamic condition for sediment resuspension. Wave-current coupling shear stress can be computed byÏ„_cw =Ï„_c+2(Ï„_c(Ï„|^)_w)^1/2sinθ+(Ï„|^)_wsin²Î¸.2)The correlation between suspended sediment concentration and turbidity(NTU) is SSC=15.908×ln(NTU)+7.0888(n=33,R²=0.7209), detrial organic carbon is the most large organic carbon pool, which accounts for 81.87% of total POC pool.3)The critical shear stress for sediment resuspension is about 0.059 N/m², the correlation between suspended sediment concentration and critical shear stress can be expressed byÏ„_cw= 238.06 SSC + 25.215(n=25, R² = 0.7298); The maximal stress depth is 8.81 cm; the magnitude of sediment resuspension flux is 10^-5～10^-6 kg·m^-2·s^-1. The critical wind speed is about 5.51 m/s, sediment is on the resuspension condition about 171 days in the whole year. The suspended sediment concentration by resuspension can be predicted by SSC = 25.23W^0.92/2.67+〔SSC(0)-25.23W^0.92/2.67〕e^-(2.67t/h).4)Total nitrogen in the sediment range from 313.09¹094.44ug/g and is mainly composed of organic nitrogen, which accounts for 60.86%. Exchangeable nitrogen is the dominant forms of inorganic nitrogen, occupies 71.40% of inorganic nitrogen. Among different forms of exchangeable nitrogen, NO₃^--N is the main form. The TOC/TN ratio ranged from 6.12¹1.88, averaging 9.38, which means the mixing source of organic matter.The main form of total phosphorus in sediments is inorganic phosphorus, which accounts for 73.33%; Among different forms of inorganic phosphorus, calcium-phosphorus is the dominant forms, accounts for 45.22% of total phosphorus; Bioavailable phosphorus in sediments occupies 86.54% of the total phosphorus pool. The potential ecological risk indices (RI) are about 36.17, which means the potential ecological risk of heavy metal in Sungo Bay is light.5)The function of resuspended sediment is as follows: nitrogen and phosphate source in Spring; nitrogen sink and phosphate source in Summer&Autumn; nitrogen and phosphate sink in Winter.