Effects of an Enhanced Flood on Riparian Plants of the River Murray, South Australia

In October 2000, the flow of the River Murray entering South Australia was increased from 32 000 to 42 050 ML day 1 by release of water from an offstream reservoir, and a downstream weir was raised by 500 mm to impound the flood and enhance local floodplain inundation. The flood was maintained for about two weeks, although the duration of inundation was longer at low elevations on the floodplain. Vegetation at three sites was surveyed before and after the flood to examine the impact of inundation on the growth and germination of flood-tolerant, flood-dependent and flood-intolerant species. Among 32 recorded species, Atriplex vesicaria (bladder saltbush, Chenopodiaceae), Sporobolus mitchellii (rats tail couch, Graminae) and Sarcocornia quinqueflora (samphire, Chenopodiaceae) accounted for nearly 82% of the total cover/abundance. Flood-tolerant and flood-dependent species (e.g. S. mitchellii) grew and germinated and flood-intolerant species (e.g. A. vesicaria) senesced. No aquatic plants germinated or established, despite favourable conditions, suggesting an impoverished seed bank or grazing. Based on the growth but lack of germination of flood-tolerant and flood-dependent species, the value of small, occasional interventions in environmental flow management may be to maintain existing communities rather than restore degraded ones. Copyright # 2004 John Wiley & Sons, Ltd. key words: Murray-Darling Basin; floodplain; riparian vegetation; weir; flood; restoration; seedbank