EFFECTS OF WATER-LEVEL CHANGES INDUCED BY WEIRS ON THE DISTRIBUTION OF LITTORAL PLANTS ALONG THE RIVER MURRAY, SOUTH-AUSTRALIA

In 1988 a survey was made of the River Murray between Locks 2 and 4 (1 53 river-km) to determine whether the distributions and relative abund ances of littoral plants are influenced by water-level variations asso ciated with weir operations. Of 20 recorded plant species, some, inclu ding Cyperus sp. and Myriophyllum verrucosum, occurred in regions down stream of each weir and hence were exposed to maximal variation in riv er levels. Others, notably Typha spp., favoured the regions above each weir, where levels are comparatively stable. The influences of physic al channel characteristics such as bank slope, bank erosion and sedime nt composition and of other environmental factors were not clear. Thes e effects may have been obscured by differences in the natures of the two pools and by a tendency for factors correlated with the water-leve l gradients to be 'reset' at each weir. Changes in the flow behaviour of the river since 1990 suggest that these survey data may later prove useful in evaluating the effects of high turbidities associated with regulated flows from the Darling River.