Nutrient compositions of cultured Skeletonema costatum,Chaetoceros curvisetus,and Thalassiosira nordenskildii

We cultured different-sized fractions of dominant phytoplankton species,Skeletonema costatum,Chaetoceros curvisetus,and Thalassiosira nordenski ldii,collected in different sea areas in various seasons,and measured and compared their C,N,P,Si contents.The N content of these species is similar,while the C,P,and Si contents of S.costatum from eutrophic Changjiang (Yangtze River) estuary are higher than those from Jiaozhou Bay (JZB),particularly the content of Si.The C,N,P,and Si contents of cultured phytoplank...     

Nutrient compositions of cultured Skeletonema costatum, Chaetoceros curvisetus, and Thalassiosira nordenskiöldii

We cultured different-sized fractions of dominant phytoplankton species, Skeletonema costatum, Chaetoceros curvisetus, and Thalassiosira nordenskiöldii, collected in different sea areas in various seasons, and measured and compared their C, N, P, Si contents. The N content of these species is similar, while the C, P, and Si contents of S. costatum from eutrophic Changjiang (Yangtze River) estuary are higher than those from Jiaozhou Bay (JZB), particularly the content of Si. The C, N, P, and Si contents of cultured phytoplankton in JZB increase with size fraction augmentation, and the percentages of C, N, and P follow the same trend, while the percentage of Si remain constant. Moreover, S. costatum from small-sized fraction assimilated Si more easily than C. curvisetus and T. nordenskiöldii, which is explained by the dominance of S. costatum under the conditions of low SiO₃-Si concentration in JZB. The C, N, P, and Si contents of cultured S. costatum collected during summer and winter are higher, which is consistent with the phytoplankton blooming seasons in JZB. The SiO₃-Si concentration of seawater during spring restrain the growth of phytoplankton, supported by the fact that the N, P, and Si contents and their ratios in cells of cultured S. costatum are low in spring season.     

长江口及其邻近水域硅酸盐的公布变化特征

Based on the data obtained from quarterly investigations in the Changjiang estuary and its adjacent sea areas in 2004,the distributions and variations of SiO₃-Si are discussed. The reslts show that the concentrations of SiO₃-Si were higher near the changjiang estuary and lower outside ghe sea.Generally,the concentrations of SiO₃-Si were higher in the surface than in the buttomin shore;the opposite distributions off shore.The SiO₃-Si concentrations both inside and outside the mouth in summer and autumn were higher than those in spring and winter.Distributions of SiO₃-Si varied with increase and decrease of runlff and with enlarge and reduce of the extent of Changjiang dilution water.The concentrations of SiO₃-Siin May were relatively less because of phytoplankton blooming. The seasonal variations of SiO₃-Si/DIN and SiO₃-Si/PO₄-P ratios were mainly controlled by the variations of SiO₃-Siconcentrations. Compared with the data of 1985-1986, the concentrations of SiO₃-Sihave inereased2.3 times,both SiO₃-Si DIN and SiO₃-Si/PO ₄-P ratios have ascended 1.6 and2.5 times respectively, which depended on the increasing of the SiO₃-Si concentrations,May is the fitting season of phytoplankton blooming compared with other seasons,in which it is the relaively least that SiO₃-Si/DIN and SiO₃-Si/PO ₄-P ratios departure from Redfield ratios. The removals of SiO₃-Siin the estuary showed that aside from biological removal, there was a main effect coming from seawater dilution.