[Hydrologic distribution characteristics of HAB frequent occurrence area in the outer Changjiant River estuary].

Based on survey data, this paper analysed the hydrologic characteristics of HAB frequent occurrence area in the outer Changjiang River estuary. The results showed that this area is an area in which the plume front with a salinity of 17-30 in the outer Changjang River estuary, the divergent surface current of the plume front and the upwelling of the high salinity Taiwan bottom warm current are coexisted. In Spring and Summer, the diluted Changjiang River water of this area changed its flow direction under the effect of southwest-northeastward current, possibly due to the large runoff from the Changjiang River to the sea. The upwelling usually occurred at the west side slope between the first turning point and the deep slot top of the outer Changjiang River estuary. This turning point was on the north side in Spring and on the south side in Summer, but in Autumn, no turning point was existed, possibly due to the small runoff. The distribution characteristics of residual current in Spring and Summer was that the adjacent area of plume front was the convergent area of surface and bottom currents, the surface residual current in the upwelling area was at divergent, and the bottom residual current had the characteristics of converging toward the Changjiang River estuary along the deep slot.