[Geochemical characteristics of nitrogen in core sediments from Sishili Bay, China].

A sequential extraction technique was applied to gain the information about the fractionation of nitrogen in four core sediments from Sishili Bay, China. Based on the binding strength of different nitrogen compounds to the sediment matrix, ranging from easy to more difficult, four forms of labile nitrogen, i. e. nitrogen in ion exchangeable form (IEF-N), nitrogen in weak acid extractable form (WAEF-N), nitrogen in strong alkali extractable form (SAEF-N) and nitrogen in strong oxidant extractable form (SOEF-N), were extracted. The results showed that the content of labile nitrogen averagely accounted for about 26.14% of total nitrogen in the surface (0-10 cm) of core sediments and decreased gradually with depth, which implied that under natural geochemical conditions only a small part of sedimentary nitrogen could participate in recycling in a short time scale. The SOEF-N was the predominant form. The average percentages of the four labile nitrogen forms were 89.7% for SOEF-N, 7.97% for IEF-N, 1.19% for WAEF-N, and 1.14% for SAEF-N, respectively. The contents of nitrogen in different labile forms at different sampling sites are influenced by the combination of environmental factors such as sediment pH, redox potential and particle size.