FLOOD-MEDIATED CHANGES IN AQUATIC MACROPHYTE COMMUNITY STRUCTURE

Sixteen artificial billabongs on the floodplain of the River Murray, N ew South Wales, were surveyed over a 14-month period to observe the ef fect of different hydrological regimes on the development of aquatic m acrophyte communities. The billabongs were initially planted with Vall isneria sp. and Myriophyllum papillosum Orch. in November 1994, then f looded. The 16 billabongs were divided into four treatments: summer fl ood, spring flood, permanent inundation, and a control treatment that was initially flooded and then allowed to vary in depth with rainfall and evaporation. The plant communities were surveyed on six occasions between April 1995 and June 1996, and percentage cover was estimated o n each sampling occasion. Fourteen aquatic macrophyte taxa were record ed over the study period. Billabongs in the permanent and summer treat ments exhibited less plant diversity than did billabongs in the contro l or spring treatments. Terrestrial plants germinated on the exposed a reas in both spring and control treatments, but not in the other treat ments.