Spatial Distribution of the Dissolved Silicate in Seawaters

The spatial and diurnal variations of dissolved silicate in the Changjiang River Estuary were investigated from May 19 to 26, 2003. The results showed 

The variation in SiOs-Si concentrations vs. time for each layer at anchor station 13 indicated that SiOs-Si concentrations on the 0 m layer was higher than that in the layer of 2 m above the bottom most of the time (Fig. 4.49). 

The variation trends of SiOa-Si concentrations vs. time in the two layers were similar viz., if SiOa-Si concentrations in one layer decreased or increased, they might decrease or increase simultaneously in another layer. The variation in SiOa-Si concentration might be significant diu-ing 4 h, especially in the layer of 2 m above the bottom where its variation might be more than 60 pmol/L. On May 22, an SiOa-Si concentration of 107.50 pmol/L decreased to 47.14 pmol/L from 13 50 to 17 50. The variation in SiOa-Si concentrations vs. time for each layer at anchor station 20 indicated that its variation is similar in the layers 0 m and 2 m above the bottom, especially in the first 24 h when the variation went all the way (Fig. 4.50). SiOa-Si concentration was the highest in the layer at 5 m, and the lowest at 20 m. Dm-ing the investigation time, the variation was the smallest in the layer at 10 m, but the biggest in the layer at 5 m. 

In order to represent the nutrient conditions in the euphotic zone, the average concentrations of nutrients in the upper 20 m in the coastal area of the ECS, and the upper 50 m in the outer continental shelf of the ECS were used for calculation, for the depth of the euphotic zone is about 20 30 m in the coastal area of the ECS, and 50 m or so in the outer continental shelf area of the ECS. The Si/N ratios were calculated by using the average concentrations of silicate and total DIN (DIN=nitrite- -nitrate- -ammonia) in the upper layer at each station. The maximal Si/N ratios were found in the 

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