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Huey J.A.,Griffith University | Schmidt D.J.,Griffith University | Balcombe S.R.,Griffith University | Marshall J.C.,Water Cooperative Research Center | Hughes J.M.,Griffith University
Freshwater Biology | Year: 2011

1.The highly variable hydrology of dryland rivers has important implications for population dynamics in these systems. In western Queensland, fluctuations in sub-population size are likely to lead to local bottlenecks and extinctions, increasing the need for connectivity and gene flow to maintain population viability. 2.Using microsatellite markers, we explored evidence for this metapopulation structure in two species of freshwater fish (Maquaria ambigua and Tandanus tandanus) and one crustacean (Macrobrachium australiense) in a sub-catchment of the upper Murray-Darling Basin, Australia. 3.Overall, we found very weak genetic structure for all three species. Two species (M. ambigua and M. australiense) showed some significant genetic structure that did not correlate with geographic distance. However, decomposed pairwise regression analysis revealed evidence for intense genetic drift at the waterhole scale, suggesting that local bottlenecks are driving what little genetic structure does exist for these species. 4.The results identify the local impact of bottlenecks on genetic diversity, but highlight the importance of gene flow in maintaining population viability in these highly variable systems. As the impacts of bottlenecks are likely to be tempered by gene flow, it is suggested that the maintenance of connectivity is of paramount importance in this dryland system. © 2011 Blackwell Publishing Ltd.

Neumann L.E.,CSIRO | Simunek J.,University of California at Riverside | Cook F.J.,CSIRO | Cook F.J.,University of Queensland | And 2 more authors.
Environmental Modelling and Software | Year: 2011

Numerical solution of the advection-dispersion equation, used to evaluate transport of solutes in porous media, requires discretization schemes for space and time stepping. We examine use of quadratic upstream interpolation schemes QUICK, QUICKEST, and the total variation diminution scheme ULTIMATE, and compare these with UPSTREAM and CENTRAL schemes in the HYDRUS-1D model. Results for purely convective transport show that quadratic schemes can reduce the oscillations compared to the CENTRAL scheme and numerical dispersion compared to the UPSTREAM scheme. When dispersion is introduced all schemes give similar results for Peclet number Pe < 2. All schemes show similar behavior for non-uniform grids that become finer in the direction of flow. When grids become coarser in the direction of flow, some schemes produce considerable oscillations, with all schemes showing significant clipping of the peak, but quadratic schemes extending the range of stability tenfold to Pe < 20. Similar results were also obtained for transport of a non-linear retarded solute transport (except the QUICK scheme) and for reactive transport (except the UPSTREAM scheme). Analysis of transient solute transport show that all schemes produce similar results for the position of the infiltration front for Pe = 2. When Pe = 10, the CENTRAL scheme produced significant oscillations near the infiltration front, compared to only minor oscillations for QUICKEST and no oscillations for the ULTIMATE scheme. These comparisons show that quadratic schemes have promise for extending the range of stability in numerical solutions of solute transport in porous media and allowing coarser grids. © 2011 Elsevier Ltd.

Vaze J.,NSW Office of Water | Vaze J.,Water Cooperative Research Center | Teng J.,NSW Office of Water | Teng J.,Water Cooperative Research Center | Spencer G.,NSW Office of Water
Environmental Modelling and Software | Year: 2010

Topography is an important land-surface characteristic that affects most aspects of the water balance in a catchment, including the generation of surface and sub-surface runoff; the flow paths followed by water as it moves down and through hillslopes and the rate of water movement. All of the spatially explicit fully distributed hydraulic and hydrological models use topography (represented by the DEM of the area modelled) to derive bathymetry. DEM is also used to derive some other key information critical in fully distributed hydraulic and hydrological models.With high-resolution DEMs such as LiDAR (Light Detection and Ranging) becoming more readily available and also with the advancements in computing facilities which can handle these large data sets, there is a need to quantify the impact of using different resolution DEMs (e.g. 1 m against 10 m or 25 m) on hydrologically important variables and the loss of accuracy and reliability of the results as we move from high resolution to coarser resolution.The results from statistical analysis carried out to compare field survey elevations with the LiDAR DEM-derived elevations, show that there are small differences between the two data sets but LiDAR DEM is a reasonably good representation of the actual ground surface compared to other commonly used DEMs derived from contour maps.The results from the analysis clearly show that the accuracy and resolution of the input DEM have serious implications on the values of the hydrologically important spatial indices derived from the DEM. The result also indicates that the loss of details by re-sampling the higher resolution DEM to coarser resolution are much less compared to the details captured in the commonly available coarse resolution DEM derived from contour maps. Topographic indices based on contour derived DEMs should be used with caution and where available, the higher resolution DEM should be used instead of the coarse resolution one. © 2010 Elsevier Ltd.

Greet J.,University of Melbourne | Greet J.,Water Cooperative Research Center | Angus Webb J.,University of Melbourne | Angus Webb J.,Water Cooperative Research Center | Cousens R.D.,University of Melbourne
Freshwater Biology | Year: 2011

Whilst it is widely recognised that a natural flow regime is important for sustaining riverine ecosystems, the relative importance of the various components of flow regime for riparian vegetation dynamics is poorly understood. We sought to determine the current extent of knowledge on the importance of seasonal flow timing for riparian plants by conducting a systematic review of the literature using causal criteria analysis. Using a definition of 'riparian' that included riverine, wetland and floodplain systems, we found sufficient evidence to provide strong support for the existence of causal relations between seasonal flow timing and a number of riparian plant processes, namely rates of waterborne dispersal (hydrochory), germination and growth, as well as riparian community composition. There was insufficient evidence to infer a causal relationship between flow timing and the reproduction or survival of riparian plants. Thus, we argue that seasonal flow timing is important for many of the processes that generate and sustain riparian vegetation communities. River regulation, and/or flow management aimed at restoring ecological values, should consider flow timing and its implication for riparian flora. Because of regulation, many of the rivers of south-eastern Australia have inverted seasonal flow patterns. Whilst direct evidence of the effects of this inversion on the flora of these rivers is lacking, the results of our causal analysis allow us to predict how these plant communities may have been affected. However, these predictions must be treated with caution because of the reliance of some of the causal analyses on wetland studies. For riverine flora, further research is particularly needed on the effects of seasonal flow timing on hydrochory, survival and reproduction. Causal criteria analysis provides a defensible and efficient means for assessing the extent of evidence for or against ecological hypotheses of this kind. In this case, systematic review of the literature provided strong evidence to support a number of causal links between seasonal flow timing and riparian vegetation dynamics, whilst also efficiently identifying knowledge gaps. © 2011 Blackwell Publishing Ltd.

Morrongiello J.R.,Monash University | Morrongiello J.R.,Water Cooperative Research Center | Bond N.R.,Monash University | Bond N.R.,Water Cooperative Research Center | And 3 more authors.
Journal of Evolutionary Biology | Year: 2010

Visual signals play a vital role in many animal communication systems. Signal design, however, often varies within species, raising evolutionarily important questions concerning the maintenance of phenotypic diversity. We analysed nuptial colour variation within and among nine populations of southern pygmy perch (Nannoperca australis Günther) along an environmental light gradient. Within populations, larger males were redder and blacker, and better-condition males were blacker. Among populations, red colour was positively correlated with the amount of orange-red light present, suggesting that males are likely optimizing signal conspicuousness by producing proportionally larger and redder patches in broad spectrum environments with more orange-red light. Signal contrast, in this regard, is maximized when red colour, appearing bright because of the prevalence of red wavelengths, is viewed against the water-column background. Together, our results are concordant with the sensory drive hypothesis; selection favours signal adaptations or signal plasticity to ensure communication efficacy is maximized in different light environments. © 2010 The Authors. Journal Compilation © 2010 European Society For Evolutionary Biology.

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