Examination of Silicate Limitation of Primary Production in Jiaozhou Bay,China II.Critical Value and Time of Silicate Limitation and Satisfaction of the Phytoplankton Growth

Analysis and comparison of Jiaozhou Bay data collected from May 1991 to February1994 revealed the spatiotemporal variations of the ambient Si(OH)4 :NO3 (Si:N) concentration ratios and the seasonal variations of (Si: N) ratios in Jiaozhou Bay and showed that the Si: N ratioswere ＜ 1 throughout Jiaozhou Bay in spring, autumn, and winter. These results provide furtherevidence that silicate limits the growth of phytoplankton (i.e. diatoms) in spring, autumn and win-ter. Moreover, comparison of the spatiotemporal variations of the Si: N ratio and primary productionin Jiaozhou Bay suggested their close relationship. The spatiotemporal pattern of dissolved silicatematched well that of primary production in Jiaozhou Bay.Along with the environmental change of Jiaozhou Bay in the last thirty years, the N and P con-centrations tended to rise, whereas Si concentration showed cyclic seasonal variations. With thevariation of nutrient Si limiting the primary production in mind, the authors found that the range ofvalues of primary production is divided into three parts: the basic value of Si limited primary pro-duction, the extent of Si limited primary production and the critical value of Si limited primary pro-duction, which can be calculated for Jiaozhou Bay by Equations (1), (2) and (3), showing thatthe time of the critical value of Si limitation of phytoplankton growth in Jiaozhou Bay is around No-vember 3 to November 13 in autumn; and that the time of the critical value of Si satisfaction of phy-toplankton growth in Jiaozhou Bay is around May 22 to June 7 in spring. Moreover, the calculatedcritical value of Si satisfactory for phytoplankton growth is 2.15 - 0.76μmol/L and the critical val-ue of Si limitation of phytoplankton growth is 1.42- 0.36 μmol/L; so that the time period of Silimitation of phytoplankton growth is around November 13 to May 22 in the next year; the time peri-od of Si satisfactory for phytoplankton growth is around June 7 to November 3. This result also ex-plains why critical values of nutrient silic