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Indicators of ecological health are problematic for wetlands in dry regions because distinctive communities are associated with dry and wet phases of indefinite duration. The propagule bank, including the resting stages of aquatic animals and plants, maintains the community's capacity to recover from drought or disturbance. This paper recordsobservations of invertebrates, protists and algae emerging in laboratory microcosms following the inundation of dry sediments from two temporary lakes on the River Murray floodplain in South Australia. A simple experiment carried out on the sediment from one lake showed thatincreased salinity was associated with lower diversity (richness) but higher abundance of emergent organisms. The effect on diversity wasevident at salinities above 11-17 mS cm-1, and the effecton abundances was evident above 6-11 mS cm-1 (salinity here is indicated by electrical conductivity at 25 deg. C). These data suggest that propagule banks may be useful as complementary indicators of wetland health. [ABSTRACT FROM AUTHOR]

The composition and distribution of littoral vegetation in four weirpools of the lower Murray were surveyed in summer 1994. Between-weirgradients in the amplitude of water level fluctuations were reflected in the typical distributions of plants, with a 4-6 m elevational range in upper-pool sites, where levels fluctuate most, and a 1-1.5 m band in the lower-pool sites, where levels are more stable. Forty-one of 48 species occurred across much of the longitudinalx elevational site matrix within this cone-shaped distribution, indicating considerable tolerance to flooding and exposure; this was especially apparent for Phragmites australis, Cyperus spp. and Centipeda spp. The 41 species were represented in seven of nine water-regime groups identified by cluster analysis. The remainder, found within 1 m of the water surface in lower-pool reaches, were aquatic macrophytes such as Vallisneria americana and Typha spp. and amphibious mudmats' such as Glossostigma elatinoides. Water regimes at given sites were measured by the number of days in 2 years flooded to any depth (>0 cm), or to 0-30 cm,and by days exposed by >100 cm. Inter-pool differences in the mediannumber of days flooded to >0 cm and 0-30 cm were 3-30% and <8%, respectively, for all species except Typha spp. but an order of magnitudefor the number of days exposed by >100 cm. However, eight of 14 common or representative species analysed showed significant inter-pool differences in the number of days flooded to >0 cm, indicating that sufficient variation exists to necessitate considerable intra-pool replication to allow for the detection of statistical differences in a multi-pool experiment. The practice of maintaining stable weir pool levels limits vegetation processes, e.g. germination, recruitment, decomposition. An increase in the amplitude of river level fluctuations during low flows, from the current 10-20 cm range to 20-50 cm, would reinstate water regimes suitable to the majority of species surveyed [ABSTRACT FROM AUTHOR]

Selected water regime indices are used to describe the tolerances toflooding and exposure of littoral and floodplain plants of the RiverMurray, South Australia. The cover and abundance of 26 perennial species were surveyed at 12 sites along a reach where water levels were influenced by weir operations. Six indices were measured: days when water depths were 0, 0-20, 20-60 and 200 cm; days when plants were exposed to 100 cm of water; and days of longest exposure to water. Ordinations of plant abundances were correlated with the frequency of flooding to 0-20 and 20-60 cm, and exposure to 100 cm. Five species clusters were apparent, these being common floodplain species (e.g. Muehlenbeckia florulenta), uncommon floodplain species (e.g. Eleocharis acuta), species from the infrequently flooded littoral (e.g. Bolboschoenus caldwellii), species from the permanently flooded littoral (e.g. Vallisneria americana) and widespread, common species tolerant to flooding and exposure (11 species, including Phragmites australis, Cyperus gymnocaulos and Bolboschoenus medianus). Half of the 26 species occurred in at least four of seven regimes suggested by cluster analysisof water regime indices, thus indicating a broad tolerance to flooding and exposure. Preferred water regimes are summarised using minimumand maximum values and quartiles for the six indices, and similarities between preferences are illustrated by a model based on minimum spanning tree techniques. [ABSTRACT FROM AUTHOR]