DISTRIBUTION CHARACTERISTICS OF NUTRIENTS IN CHINESE BOHAI SEA

Nutrients are key environmental factors in marine ecosystem. They limit algal growth when at low concentrations and cause algal bloom when at high contents. They also control the growth and succession of many other biota including bacteria and zooplankton, either directly or indirectly. Nutrient contents therefore affect both the structure and functions of marine ecosystem. To study the contents and distribution of nutrients in Chinese Bohai Sea, two cruise surveys were undertaken in August 2000 (summer) and January 2001 (winter), respectively. A total of 595 water samples were collected from 91 sites. After collection the samples were transported to the laboratory and five nutrients, i.e., nitrate, nitrite, ammonia, phosphate and silicate, were analyzed. The results showed that tile average concentration of total inorganic nitrogen (TIN) in Bohai Sea in winter (6.5293.717 ${\mu}$mol$.$l$\^$-1/) was significantly higher than that in summer (3.717 ${\mu}$mol$.$l$\^$-1/). The phosphorus concentration in winter (0.660 ${\mu}$mol$.$l$\^$-1/) was also significantly higher than that in summer (0.329 ${\mu}$mol$.$l$\^$-1/). Mean silicate concentration in winter (7.858 ${\mu}$mol$.$l$\^$-1/) was not significantly different from that in summer (7.200 ${\mu}$mol$.$l$\^$-1/). Nutrients also varied considerable among different areas within Bohai Sea. TIN concentration in Laizhou Bay (4.444 ${\mu}$mol$.$l$\^$-1/), for example, was significantly higher than those in Bohai Bay (2.270 ${\mu}$mol$.$l$\^$-1/) and Bohai Straight (2.431 ${\mu}$mol$.$l$\^$-1/), which probably reflects tile discharge of large amounts of nitrogen into Laizhou Bay via Yellow River. The nutrients also showed vertical distribution pattern. In summer, nutrients in bottom layer were generally higher than those in surface and medium layers. In winter, however. nutrients in different layers were not significantly different Compared with historic data, TIN contents increased continuously since early 1980s, phosphorus arid silicone contents, nevertheless, fell down to some degree. Based on atomic ratios of different nutrients, nitrogen is still the main limiting factor for algal growth in Bohai Sea.