Keith F. Walker

Flow variability and the ecology of large rivers

Ecological processes in large rivers are controlled by their flow variability. However, it is difficult to find measures of hydrological variability that characterize groups of rivers and can also be used to generate hypotheses about their ecology. Multivariate analyses of the hydrographs of 52 rivers worldwide revealed distinctive patterns of flow variability that were often correlated with climate. For example, there were groups of rivers that corresponded broadly with ‘tropical’ and ‘dryland’ climates. However, some rivers from continental climates occupy both extremes of this range, illustrating the limitations of simple classification. Individual rivers and groups of rivers may also have different hydrographic ‘signatures’, and attempts to combine measures of hydrological variability into indices mask biologically significant information. This paper identifies 11 relatively independent measures of hydrological variability that help categorize river types and are each associated with aspects of fish biology. Ways are suggested by which the Flood Pulse Concept can be expanded to encompass hydrological variability and accommodate differences among groups of rivers from different climatic regions. Such recognition of the complex role of hydrological variability enhances the value of the concept for river conservation, management and restoration.

A review of the ecological effects of river regulation in Australia

Responses to hydrologic change are an important theme in lotic ecology, and data for Australian rivers are accumulating in a rapid, butad hoc manner. Thia paper arranges recent contributions according to the major drainage divisions, which provide reasonably coherent environmental units. The east coastal rivers are exploited for storage, power generation and waste disposal, and Tasmanian rivers are regulated to serve hydro-electric power schemes. Most information refers to the Murray-Darling river system, which supplies irrigated agriculture in semi-arid inland areas of S.E. Australia, and is intensively regulated by dams, weirs and barrages. The Murrays flows are over-committed, if variability is taken into account, and there are environmental problems (e.g. erosion and salinity) associated with irrigation. The effects of regulation are seen also in the changed distributions of plants and animals associated with the Murray and its floodplain. In Australia the national effort is uncoordinated because research and management are developing independently of one another. Ecologists must become involved in the planning and implementation of strategies that are consistent, as far as possible, with offstream and instream needs.

Hydrological persistence and the ecology of dryland rivers

The flow regime of Cooper Creek, central Australia, is subject to a summer-monsoonal climate and aseasonal cycles associated with the El Nino–Southern Oscillation (ENSO). Analysis of a 48-year hydrograph indicates that floods tend to occur in clusters associated with La Nina episodes. The influence of ENSO is apparent in lagged correlations between discharge and values of the Southern Oscillation Index (SOI), and in measures of coherency derived from cross-spectrum analysis. Hydrological persistence is indicated by partial auto-correlations between floods in successive years. In a cluster of five floods over 1987–1991, cumulative effects were apparent in wetland habitat areas, in water temperature and transparency, and in the recruitment patterns of five fish species: Nematalosa erebi (Clupeidae), Hypseleotris klunzingeri (Gobiidae), Melanotaenia splendida tatei (Melanotaeniidae), Retropinna semoni (Retropinnidae) and Gambusia holbrooki (Poeciliidae). During serial floods, native fish appear to have a recruitment advantage over the exotic Gambusia. Hydrological persistence and its ecological correlates warrant consideration in research, planning and management, particularly in regard to the water resources of arid and semi-arid regions. Copyright

A Ramsar wetland in crisis – the Coorong, Lower Lakes and Murray Mouth, Australia

The state of global freshwater ecosystems is increasingly parlous with water resource development degrading high-conservation wetlands. Rehabilitation is challenging because necessary increases in environmental flows have concomitant social impacts, complicated because many rivers flow between jurisdictions or countries. Australia’s Murray–Darling Basin is a large river basin with such problems encapsulated in the crisis of its Ramsar-listed terminal wetland, the Coorong, Lower Lakes and Murray Mouth. Prolonged drought and upstream diversion of water dropped water levels in the Lakes below sea level (2009–2010), exposing hazardous acid sulfate soils. Salinities increased dramatically (e.g. South Lagoon of Coorong >200 g L–1, cf. modelled natural 80 g L–1), reducing populations of waterbirds, fish, macroinvertebrates and littoral plants. Calcareous masses of estuarine tubeworms (Ficopomatus enigmaticus) killed freshwater turtles (Chelidae) and other fauna. Management primarily focussed on treating symptoms (e.g. acidification), rather than reduced flows, at considerable expense (>AU

Tolerance of riverine plants to flooding and exposure indicated by water regime

2 billion). We modelled a scenario that increased annual flows during low-flow periods from current levels up to one-third of what the natural flow would have been, potentially delivering substantial environmental benefits and avoiding future crises. Realisation of this outcome depends on increasing environmental flows and implementing sophisticated river management during dry periods, both highly contentious options.

Changes in biofilms induced by flow regulation could explain extinctions of aquatic snails in the lower River Murray, Australia

Selected water regime indices are used to describe the tolerances to flooding and exposure of littoral and floodplain plants of the River Murray, 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 analysis of water regime indices, thus indicating a broad tolerance to flooding and exposure. Preferred water regimes are summarised using minimum and maximum values and quartiles for the six indices, and similarities between preferences are illustrated by a model based on minimum spanning tree techniques. Copyright

Species boundaries in carp gudgeons (Eleotrididae : Hypseleotris) from the River Murray, South Australia: evidence for multiple species and extensive hybridization

Notopala sublineata, Notopala hanleyi(Viviparidae) andThiara balonnensis (Thiaridae) are prosobranchgastropodsthat were once abundant in the lower River Murray. These andothersnail taxa have declined markedly over the last 50 years,coinciding with increased flow regulation by dams and weirs.Inthis paper we speculate that the decline may be linked tochangesin the nature of food resources. Before regulation, most ofthebiofilm biomass in the lower Murray probably was microbial, asfluctuating water levels and high turbidity would havemaintainedthese communities in a state of early succession. Bystabilisingseasonal water levels, we suggest that regulation has promotedthegrowth of filamentous algae, perhaps at the expense ofbacteria.Evidence from gut and faecal pellet analysis, and fromanalysis ofcarbon stable-isotopes, suggests that the gastropod taxa aredetritivores, feeding mainly on amorphous organic detritus.Algaehave a relatively high C:N ratio (low nutritional value) andmay bean inadequate food to maintain female growth and reproduction,especially in viviparous snails.

A synopsis of ecological information on the saline lake rotifer Brachionus plicatilis Müller 1786

Allozyme analyses of carp gudgeons (Hypseleotris) from five sites in the lower River Murray revealed three distinctive taxa designated HA, HB and HC, diagnosable from one another by fixed differences at 3–5 loci, and three apparent F 1 hybrid forms, HA¥HB, HA¥HX and HB¥HX, where HX denotes a taxon not sampled in its ‘pure’ form. Of all fish sampled, 25% were hybrids, although only one hybrid form was found at any one site, and never in company with both parental taxa. No hybrids involving HC were found, although this was the most common taxon, and no HA¥HB hybrids were present at the one site of demonstrated sympatry between the parental taxa. Morphological analysis and the lack of introgression confirm that HA, HB, and HC are distinct biological species. Partial meristic data suggest that HC corresponds to H. klunzingeri s.l., ‘Midgley’s carp gudgeon’ is a composite of HA, HB and HA¥HB hybrids, and ‘Lake’s carp gudgeon’ may be a composite of HX and one of its hybrids (HB¥HX). We speculate that one or more of the hybrid classes may be ‘unisexual lineages’ (clonally reproducing, usually all-female forms derived from hybridization between congeners).

Spatial distribution of littoral invertebrates in the lower Murray-Darling River system, Australia

The rotifer Brachionus plicatilis Muller, shown in Fig. 13.1, is a cosmopolitan inhabitant of inland saline and coastal brackish waters. It tolerates a remarkable range of environmental conditions and, especially in alkaline (soda) lakes, may attain very high population densities. Like the familiar brine-shrimp Artemia, and the green alga Dunaliella, B. plicatilis is used widely as a basic food in the intensive culture of certain marine crustaceans and fishes. Indeed, most ecological knowledge of the species stems from its significance in mariculture (e.g. Solangi & Ogle, 1977).

Water regimes and littoral plants in four weir pools of the River Murray, Australia

The abundance and richness of macroinvertebrates in the lower Murray and Darling rivers were examined at a macroscale (rivers), mesoscale (billabongs, backwaters, channel) and microscale (vegetation, snags, substrata). In the Darling, insects dominated (85% of taxa, 81% of individuals); the richest taxa were Diptera (26 taxa) and Coleoptera (15 taxa) and the most abundant were Hemiptera (47%) and Diptera (35%). In the Murray, insects again dominated (84% of taxa, 52% of individuals), particularly Diptera (22 taxa), Coleoptera (12 taxa) and Hemiptera (9 taxa), but there were more crustaceans (9% of taxa, 47% of individuals, particularly the atyid shrimp Paratya australiensis). Both assemblages were uneven: in the Darling, >50% of biomass was Micronecta spp. (Corixidae), Dicrotendipes sp. (Chironomidae) and Macrobrachium australiense (Palaemonidae); in the Murray, 70% of biomass was P. australiensis and Caridina mccullochi (Atyidae) and the insects Micronecta spp. (Corixidae) and Chironomus sp. (Chironomidae). Abundances generally were greatest in the Murray. Hydrologic and geomorphic factors influenced assemblages at the macroscale, whereas microhabitat diversity dominated at the mesoscale.