GEOCHEMICAL CHARACTERISTICS OF NITROGEN AND THEIR ENVIRONMENTAL SIGNIFICANCE IN JIAOZHOU BAY SEDIMENTS
胶州湾沉积物中氮的地球化学特征及其环境意义*

Nitrogen plays an important role in global biogeochemical cycle and may serve as an efficient proxy for marine sedimentary environmental changes. The biogeochemical cycle of nitrogen is a very complicated process and affected by many physical, geochemical, and biological factors. Up till now, the research about nitrogen is mainly focused on the early diagenisis cycle (including mineralization, nitrification, denitrification, and so on) and the benthic flux of nitrogen of sediment-water interface. This research has resulted in a systematic understanding about the nitrogen cycle. However, nitrogen forms, distributions, and its relationship with other biogenic elements in nitrogen cycle have seldomly been involved. This paper presents the nitrogen species employing sequential extraction technique. The transferable nitrogen in Jiaozhou Bay sediments can be divided into four species, namely the ion exchangeable form (IEF-N), the weak acid extractable form (WAEF-N), the strong alkaline extractable form (SAEF-N), and the strong oxidant extractable form (SOEF-N) according to their different bonding strength to sediments. The geochemical characteristics of nitrogen in Jiaozhou Bay sediments as well as the controlling factors and the environmental significances were given in the paper associated with 210Pb chronological studies. The results show that the SOEF-N is the primary form of transferable nitrogen and the NO3-N is the dominant form in Jiaozhou Bay sediments. The SAEF-N is the dominant form of inorganic nitrogen. The IEF-N is the most active transferable nitrogen and the WAEF-N accounted for least part of nitrogen in Jiaozhou Bay sediments. The concentrations and burial fluxes of nitrogen were controlled by many environmental factors including pH, salinity, temperature, particle size and etc. Also, nitrogen has some correlation with the phytoplankton and their spatial distributions are similar. Results also present sedimentation rate changes in the past hundred years and the corresponding years of every layer in Jiaozhou Bay sediments were also displayed in the paper. In addition, based on the burial flux of nitrogen, at the beginning of the 20th century, the pollution in the Jiaozhou Bay was not serious and the burial flux of nitrogen was very low. Since the 1980s, the burial flux of nitrogen increased abruptly due to greatly strengthened human activities. However, the recent years efforts of controling pollution has improved the environment of the Jiaozhou Bay apparently. Our investigation confirms that the burial flux of nitrogen can be a good proxy indicating environmental changes of the Jiaozhou Bay.