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Greet J.,University of Melbourne | Greet J.,eWater Cooperative Research Center | Cousens R.D.,University of Melbourne | Webb J.A.,University of Melbourne | Webb J.A.,eWater Cooperative Research Center
Plant Ecology

Changes to the timing of peak river flows caused by flow regulation affect riparian vegetation composition, but the mechanisms driving such vegetation changes are not well understood. We investigated experimentally the effects of timing of inundation on riparian plant growth and flowering. We collected 168 sods from 14 sites across five lowland rivers in south-eastern Australia. Plant cover and flowering within the sods were surveyed each season for a year. During this period, sods were inundated for 6 weeks in either early spring or in summer. Terrestrial plant taxa (which included most exotic species) senesced in response to inundation, regardless of its timing. In contrast, native amphibious species (particularly amphibious forbs) responded favourably to inundation in spring, but were unaffected by inundation in summer. Native and exotic emergent macrophytes responded favourably to inundation regardless of timing, and flowered frequently in both the spring- and the summer-inundation treatments. In contrast, many native annuals flowered only in the spring-inundation treatment, while more exotic grasses flowered in the summer-inundation treatment. In temperate climates, inundation in early spring followed by non-flooded conditions is likely to be important for promoting the growth of amphibious forbs and the recruitment and flowering of riparian annuals. Without inundation in spring, many terrestrial exotic weeds may flourish and set seed prior to any subsequent inundation (e. g. in summer). We contend that natural seasonal timing (i. e. winter-early spring) of flow peaks is important for the maintenance of native riverbank vegetation and reducing the extent of terrestrial exotic species within the riparian zone. © 2012 Springer Science+Business Media Dordrecht. Source

Lane P.N.J.,University of Melbourne | Lane P.N.J.,eWater Cooperative Research Center | Feikema P.M.,University of Melbourne | Sherwin C.B.,University of Melbourne | And 3 more authors.
Environmental Modelling and Software

Disturbance of forested catchments by fire, logging, or other natural or human induced events that alter the evapotranspiration regime may be a substantial threat to domestic, environmental and industrial water supplies. This paper describes the physically-based modelling of the long term changes in water yield from two wildfire affected catchments in north-eastern Victoria, Australia, and of fire and climate change scenarios in Melbourne's principal water supply catchment. The effect of scale, data availability and quality, and of forest species parameterisation are explored. The modelling demonstrates the importance of precipitation inputs, with Nash and Sutcliffe Coefficients of Efficiency of predicted versus observed monthly flows increasing from 0.5 to 0.8 with a higher density of rainfall stations, and where forest types are well parameterised. Total predicted flow volumes for the calibrations were within 1% of the observed for the Mitta Mitta River catchment and <4% for the Thomson River, but almost -10% for the less well parameterised Tambo River. Despite the issues of data availability simulations demonstrated the potential for significant impacts to water supply in SE Australia from wildfire and climate change. For example, for the catchments modelled the moderate climate change impact on water yield was more pronounced than the worst fire scenario. Both modelled cases resulted in long term water yield declines exceeding 20%, with the climate change impact nearing 30%. A simulation using observed data for the first four post-fire years at the Mitta Mitta River catchment showed Macaque was able to accurately predict total flow. © 2009 Elsevier Ltd. Source

Greet J.,University of Melbourne | Greet J.,eWater Cooperative Research Center | Cousens R.D.,University of Melbourne | Webb J.A.,University of Melbourne | Webb J.A.,eWater Cooperative Research Center
River Research and Applications

Natural flow regimes are important for sustaining riverine vegetation. The regulation of river flows to provide water for agriculture often results in changes to flow timing. This study assesses the impact of altered seasonal flow patterns on riverine flora. Within temperate Australia, we surveyed the vegetation of five lowland rivers, three of which have large dams that alter their seasonal flow patterns; the other two are unregulated. From four to six sites were selected on each river, and these were classified into three levels of regulation based on the extent to which the timing of their seasonal flow patterns were altered. Sites were surveyed in winter and the following summer. Permanent quadrats were also established at a number of the surveyed sites and resurveyed every 3months. Of the 267 plant taxa identified, 145 were exotic (non-native). More exotic taxa and fewer native taxa were associated with increasing level of seasonal flow inversion (regulation). In particular, greater numbers of short-lived exotic terrestrial taxa and fewer native woody taxa were associated with increasing level of regulation. Some exotic woody species (e.g. willows) were more common in the unregulated rivers and may have life-history traits favoured by the natural seasonal flow patterns of study area. Multivariate analyses showed that level of regulation had a significant effect on the overall composition of the riverine vegetation. Our results provide support for the hypotheses that flow regulation adversely affects native species diversity and increases the vulnerability of riparian zones to invasion by exotic species; however, these effects are dependent on plant species' life-history strategies. Our study highlights the importance of natural seasonal flow patterns for sustaining native riverine plant communities. Flow management aimed at maintaining or restoring ecological values should consider seasonal flow patterns. Winter/spring flow peaks may be particularly important for the recruitment of native riverine plants, especially trees and shrubs, and reducing the extent of exotic annuals and grasses. © 2012 John Wiley & Sons, Ltd. Source

Morrongiello J.R.,Monash University | Morrongiello J.R.,eWater Cooperative Research Center | Bond N.R.,Monash University | Bond N.R.,eWater Cooperative Research Center | And 3 more authors.
Freshwater Biology

Dissolved organic carbon (DOC) can induce lethal and sub-lethal effects in exposed biota via hypoxic blackwater events and the toxicity of leached compounds. Little is known of how DOC exposure affects fish reproduction despite the fact that its release can coincide with spawning-associated flow pulses. River red gum (Eucalyptus camaldulensis) leaf leachate is a major source of DOC in Australian freshwaters and includes the toxic plant secondary metabolites polyphenols and tannins. High concentrations of leachate are released when leaves on floodplains or dry stream channels are inundated by water. Southern pygmy perch (Nannoperca australis) from naturally high and naturally low Eucalyptus leachate environments in south-east Australia were exposed to elevated leachate levels to investigate the effects of DOC on reproduction and to explore whether response patterns were consistent with populations becoming locally adapted to historical leachate levels. Fish exposed to leachate were half as likely to reach sexual maturity as control fish. Fish from a naturally high-exposure population tended to reach sexual maturity earlier than those from a naturally low-exposure population. Leachate exposure had no effect on either egg size or fecundity. Our results suggest that leachate-exposed mothers did not reproduce because they were physiologically stressed or perceive the environment to be unsuitable, which raises the potential of plastic or adaptive responses to this stressor. The negative sub-lethal effects observed have important fitness implications for individuals, the viability of populations and the management of environmental flows and riparian zones. © 2011 Blackwell Publishing Ltd. Source

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