Effects of rainfall and salt‐wedge movement on phytoplankton succession in the Swan–Canning Estuary, Western Australia

AbstractAnnual data sets, from 1980–81 and 1994–95, provide evidence that inter‐annual differences in the seasonal succession of phytoplankton in the Swan River Estuary can be attributed to rainfall and salt‐wedge movement. The distribution and succession of phytoplankton are influenced by seasonal variation of rainfall and its subsequent effect on the spatial distribution of salinity. The longer duration of rainfall in 1980–81 compared with 1994–95 effectively restricted the movement of the salt‐water wedge, thereby delaying the progression of marine phytoplankton into the estuary. There was little difference in the phytoplankton composition and biomass in the lower estuary, while the upper estuary appeared to have more blooms of dinoflagellates in the summer and autumn of 1994–95 compared with 1980–81.The intensity and duration of rainfall appeared to affect the availability of soluble nutrients. Although there was no significant difference in phytoplankton biomass between the two periods, it was likely that the high phytoplankton biomass in the upper estuary in 1994–95 was due to availability of more soluble nutrients from internal recycling processes at the sediment/water interface. Copyright © 2001 John Wiley & Sons, Ltd.