Abstract: Three undisturbed cores were sampled from the tidal zone of Jiaojiang estuary of Zhejiang in the May of 2003. The study mainly focused on acid volatil sulphide (AVS) and simultaeously extracted metals (SEM) by using cold HCl extruction techniques to digest each sample, and by the iodine method to measure AVS and by ICP-MS(or ICP-AES) to measure trace metals (or Fe). The formation processes has been analysed for sediment profiles of trace metals at high tide, midst tide and low tide land. Futhermore, the chemical activtity and bioavailability of trace metals in various tidal zones have been evaluated based on the molar ratio of SEM-Me/AVS. The results suggest that the layer with the ratio of SEM-Me/AVS more than 1 is thiner than 6cm at high tidal or low tidal land, which indicate that the trace metals appear to be of less reactive or unbioavailability, and is thick (around 26 cm) at the midst tide land, which suggest that the trace metals are more reactive or bioavailability. Moreover, there is an organic carbon highly riched layer in the upmost sediments (it may be several millimetre).

Key words: Jiaojiang estuary, tidal zone, acid volatile sulfide(AVS), simultaneously extracted metals(SEM), bioavailability