Forms Of Nitrogen In Different Grain Size Sediments And Its Functions In Biogeochemical Cycling Of The Yellow Sea

mineralization rate of organic matters was the quickest in the coarse sediments. The constants of organic matters decomposing rate in different grain size sediments were 42.28×10-3(coarse sediments),20.48×10-3(medium size sediments)and 5.37×10-3(fine sediments)respectively, which showed that the decomposing rate constant in coarse sediments was about ten times of that in fine sediments, and 2 times of that in medium size sediments. This may be the reason that the contents of different forms of nitrogen in coarse sediments are the lowest in the northern Yellow Sea.4. The potential ecological functions of nitrogen and its effects on the biogeochemical cycling were revealed. The forming and releasing of various forms of nitrogen in different grain-size sediments were affected by environment. The contents of DO was the predominant factor to control nitrogen forms and their releasing. In addition, the temperature, salinity, pH, and the contents of NH4 and NO3 + - of the overlying water could also affect the different forms of nitrogen releasing. The different forms of transferable nitrogen in different grain-size sediments had different influence on marine biology. Generally, the contents of the different transferable forms of nitrogen in fine sediments were related to the phytoplankton and benthos, and that in coarse and medium size sediments were closely related zooplankton. In the four transferable forms of nitrogen in different grain size sediments, the SOEF-N and SAEF-N could increase the productivity by accelerating the growth and reproduce of phytoplankton. On the whole, no matter what form the nitrogen existed, its potential ecological function could not be displayed until it was transferred into NH4-N or NO3-N. The burial efficiency of nitrogen was different in different sea area. In the southern Yellow Sea, the burial efficiency was the highest in coarse sediments and lowest in fine sediments. The highest burial efficiency could be up to 30.21%, and the lowest was only 16.52%, so exceeding 70% of nitrogen could be released to take part in recycling in the southern Yellow Sea. In the northern Yellow Sea, the burial efficiency of inorganic nitrogen was lower, and that of organic and total nitrogen were higher. This resulted that much of the inorganic nitrogen could be released to the overlying water to take part in recycling (including more than 85% of IEF-N, 95% of WAEF-N and 77% of SAEF-N), while the proportions of SOEF-N and TN could be released were less than 56.62% and 24.01% respectively. If all the released nitrogen could take part in recycling, 19.54×109mol nitrogen could be released for marine productivity in the southern Yellow Sea surface sediments, which could contribute to 6.54% nitrogen of that the new productivity needed in this area. The northern Yellow Sea sediments could provide 12.03% nitrogen (about 65.31×107mol) for the new productivity. This showed that the released nitrogen from sediments could contribute the primary productivity to a certain degree in this area, and had important functions in the biogeochemical cycling of nitrogen.