Seasonal Variations of Nitrogen in Seawaters

1 Seasonal Distributions of Dissolved Inorganic Nitrogen in Seawaters 

An observation was conducted in the Changjiang River Estuary from May 19 to 26, 2003 (Fig. 4.2). In spatial and diurnal variations, DIN was examined. Fig. 4.21 showed the distribution of NO3-N, NO2-N along transect A. The dis- 

23 and Fig. 4.24). In the mixed water sector, the shallow depth made water mixing easy therefore, the mean nutrient concentrations showed no significant differences among the studied layers. In the seawater sector, the average concentration of NO3-N and NO2-N decreased downward (Table 4.10). 

The ratios of NO3-N, NO2-N, and NH4-N (Fig. 4.25, Chai, 2006) show that nitrate, which originated from fertilizers extensively used in the Changjiang River basin, was the dominant form of DIN in the Changjiang River Estuary and the adjacent ECS throughout the year. With the exception of winter. 

3 Long Term Change in Nitrogen in the East China Sea 

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