Study On Distribution And Speciation Of Silica In Tonkin Gulf

Based on the environmental investigation during October～November, 2007 in Tonkin Gulf, the speciation of silicon in the waters and biogenic silicon of the surface sediment were determinated. By analyzing the distribution of different speciation of phosphorus and relationship between environmental factors and different speciation of silicon in the waters and in the surface sediment, the source of phosphorus, and its source, transportation and transformation were explored. The study results can be summarized as follows:(1)The concentrations range of reactive silicate(SiO₃-Si) was (2.48～13.87)μmol/L, and the average concentrations of SiO₃-Si was(6.74±3.24)μmol/L in the sea water of Tonkin Gulf. The concentrations range of biogenous silica(BSi) was (0.11～1.16)%, and the mean concentration of BSi was (0.58±0.26)%in the surface sediment of Tonkin Gulf.The concentrations range of particulate biogenous silica (PBSi), lithogenic silicon (LSi) and particulate silicon (PSi) in suspended particle matter of Tonkin Gulf were 0.02μmol/L～6.36μmol/L, 0.47μmol/L～16.62μmol/L and 0.95μmol/L～20.09μmol/L, that average concentrations of PBSi, LSi and PSi were (1.42±1.24)μmol/L, (7.43±4.19)μmol/L and(8.85±4.66)μmol/L.(2)The mean ratio value of DIN to DIP was 29.78, and mean ratio value SiO₃-Si to DIP was more than 22, moreover, the average concentrations DIP was less than 0.1μmol/L, therefore , The restrictive nutrient of diatoms Growth and reproduction was DIP in autumn of Tonkin Gulf. LSi was the source of SiO₃-Si, but BSi of surface was the sink of PBSi in suspended particle matter.(3)The contents of SiO₃-Si,LSi and PSi were affected by the terrestrial inputs, especially Qiongzhou Strait aisle water. PBSi was affected by the input of external waters and biogeochemical process. BSi of surface sediment was significant negative correlated with salinity(S) of bottom waters, and BSi was influenced by the terrestrial inputs. The contents of SiO₃-Si, PBSi,LSi and PSi had small vertical gradient in the euphotic zone(Water depth <10 m), and the vertical distribution was uniform; But the vertical distribution of PBSi,SiO₃-Si,LSi and PSi decreased with depth first and then increased below euphotic zone waters (Water depth > 10 m).(4)SiO₃-Si was significant correlated with pH, dissolved oxygen (DO) and alkalinity (Alk) of the water. PBSi was significant correlated with SPM, pH and temperature (T). LSi was significant correlated with chlorophyll a (Chl.a), T and ALK. BSi Was significant correlated with moisture content (9), organic carbon (OC) and sulfide.(5)The transportation and transformation of different speciations of silica in waters and sediment of Tonkin Gulf can be described as: SiO₃-Si←LSi←PBSi→BSi. According to the correlation Of the different speciations of silica, if use symbol(—)as transformation process.