长江口中肋骨条藻赤潮发生过程环境要素分析──营养盐状况

ANALYSIS OF ENVIRONMENTAL FACTORS DURING OCCURRENCE OF SKELETONEMA COSTAUM RED TIDE IN CHANGJIANG RIVER ESTUARY──THE NUTRIENT STATE

从长江口1990年6月的一次中肋骨条藻赤潮发生过程中营养盐含量变化可见，由于潮汐的作用，观测水域各营养盐要素都在不同程度上存在周日波动特征，其中NO3－N在一个潮周期内变化幅度可达1倍以上。赤潮发生时表层水体NO3－N，PO4－P和SiO3－Si值都呈下降趋势，降幅最大的PO4－P达3倍以上；N／P值则急剧上升，峰值为450。随着赤潮消亡，NO3－N，NO2－N和SiO3－Si浓度很快恢复正常，NH4－N浓度在赤潮发生时略有升高，但在赤潮末期明显下降，而且恢复过程相对较长。

Eutrophication of seawater is the main cause of red tide. The nutrient concentrations of surface water were relatively higher in the red tide frequent area of theChangjiang River estuary (by Skeletonema costaum). Before red tide occurrs, thevalues of NO3-N, NO2-N, NH4-N, PO4-P, SiO3-Si, N/P averaged 36.6, 0.64, 2.43,0.83, 34.7 (μmol/dm3) and 44.6 respectively and fluctuated daily. The value ofNO3-N could vary by more than 100% during 24h. Analysing of the relationshipof nutrients and salinity showed that on the surveyed area the replenishment of NO3-N, PO4-P and SiO3-Si was mainly from coastal freshwater, and that the concentration of NH4-N was kept normal by its bio- chemical recycling. At the bloomingstage, the concentrations of NO3-N, PO4-P and SiO4-Si in the surface water reducedto some extent. PO4-P concentration was reduced to 1/3 tbat of the original conce.ntration. The concentration of NO3-N tended to increase during the peak of redtide when the value of N/P also increased rapidly to a maximum of 450.0. Duringthe bloom, the relationships between biomass and NO3-N, PO4-P and SiO3-Si showednegative correlations, but that between NO2-N, NH4-N and N/P showed positive correlations. After red tide disappeared, the values of NO3-N, NO4-N and SiO3-Sireturned rapidly to normal. The concentration of NH4-N was slightly higher duringthe peak of bloom but decreased obviously during the decline phase but renormalizedafter some time.