Evolution of Nutrients and Primary Production

DIP increased in the third stage, both DIN and DIP decreased in variational tendency however, DIN was still above its level of the early 1980s, while DIP was already below its level of the early 1980s and even reached the lowest level in the past 30 years (as shown in Figs. 2.31 and 2.32). 

In addition, the flux of DIN of the Yellow River into the Bohai Sea has the same variation trend as the evolution of the concentration of DIN in Bohai Sea waters (as shown in Fig. 2.34), especially from the middle 1990s. There was a close relationship between the flux of DIN of the Yellow River and concentrations of DIN in Bohai Sea waters from the middle 1990s (r=0.820, n—9, sig. 0.01). Consequently, the Yellow River input of DIN was an important source of nitrogen in Bohai Sea waters. 

The runoff of the Yellow River was also an important factor influencing the concentration of DIP in the Bohai Sea waters. The nmoff of the Yellow River has exhibited a decreasing trend over the past 30 years (as shown in Fig. 2.35). There was a close correlation between the runoff of the Yellow River 

Winter 1982 Skeletonema costatum Chaetoceros spp., and Asterionella japonica 

Furthermore, the phytoplankton biomass has a significant linear correlation with PP (r=0.7415, sig. 0.01, n=12) (Liu et al., 2003). Therefore, it could be supposed that equation (2.2) could describe the relationship between the phytoplankton biomass and the PP of the Bohai Sea. 

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