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Roberts D.T.,Queensland Bulk Water Supply Authority Seqwater | Mallett S.,University of Queensland | Kruck N.C.,University of Queensland | Loh W.,University of Queensland | Tibbetts I.,University of Queensland
Journal of Fish Biology | Year: 2014

This study assessed the spawning activity of the threatened Australian lungfish Neoceratodus forsteri by measuring egg densities within the artificial habitat of a large impoundment (Lake Wivenhoe, Australia). Eggs were sampled (August to November 2009) from multiple locations across the impoundment, but occurred at highest densities in water shallower than 40cm along shorelines with a dense cover of submerged terrestrial vegetation. The numbers of eggs declined over the study period and all samples were dominated by early developmental stages and high proportions of unviable eggs. The quality of the littoral spawning habitats declined over the study as flooded terrestrial grasses decomposed and filamentous algae coverage increased. Water temperatures at the spawning site exhibited extreme variations, ranging over 20·4°C in water shallower than 5cm. Dissolved oxygen concentrations regularly declined to <1mgl-1 at 40 and 80cm water depth. Spawning habitats utilised by N. forsteri within impoundments expose embryos to increased risk of desiccation or excessive submergence through water-level variations, and extremes in temperature and dissolved oxygen concentration that present numerous challenges for successful spawning and recruitment of N. forsteri in large impoundment environments. © 2014 The Fisheries Society of the British Isles. Source

Rolls R.J.,Griffith University | Stewart-Koster B.,University of Washington | Ellison T.,Griffith University | Faggotter S.,Griffith University | Roberts D.T.,Queensland Bulk Water Supply Authority Seqwater
Biodiversity and Conservation | Year: 2014

Habitat fragmentation is a key anthropogenic factor in biodiversity decline, particularly in aquatic ecosystems. We predicted that differences in fish assemblage composition due to the impact of fragmentation would most strongly affect migratory species, and these effects would be dependent on the interaction between the characteristics of each barrier and the antecedent flow conditions that determine temporal variation in connectivity. These hypotheses were applied to a coastal river network in eastern Australia that is fragmented by multiple weirs and dams, including some with passage facilities. How these facilities interact with flow to mediate hydrological connectivity and hence patterns of community structure is unknown. Five distinct assemblages were identified that were associated with different combinations of environmental factors and barrier characteristics (spatial arrangement, passability), and key differences were due to variation in migration traits. Two spatially distinct assemblages were associated with fragmentation by two impassable barriers. However, the migration traits that accompanied these community changes were inconsistent between these groups, and likely reflected effects of barriers near the estuary and in the middle of the stream network on diadromous and freshwater-migratory species, respectively. Two assemblage groups in the vicinity of passable weirs varied temporally as a function of hydrology and the seasonal upstream movement of juvenile diadromous species. The effect of habitat loss in conjunction with fragmentation was evident, with a further assemblage group occurring in reaches where riparian vegetation and instream habitat have been altered by poor management of agriculture. This study indicates that the impact of habitat fragmentation in rivers depends on the interaction of the migration characteristics of biota, temporal variation in hydrology which mediates connectivity, and the location of anthropogenic barriers. Conservation policies aimed at minimizing human impacts on aquatic biodiversity need to jointly account for the separate impacts of habitat fragmentation and habitat loss. © 2014 Springer Science+Business Media Dordrecht. Source

Leigh C.,Griffith University | Burford M.A.,Griffith University | Roberts D.T.,Queensland Bulk Water Supply Authority Seqwater | Udy J.W.,Queensland Bulk Water Supply Authority Seqwater
Water Research | Year: 2010

Cyanobacterial blooms in drinking water reservoirs present a major ecosystem functioning and human health issue. The ability to predict reservoir vulnerability to these blooms would provide information critical for decision making, hazard prevention and management. We developed a new, comparative index of vulnerability based on simple measures of reservoir and catchment characteristics, rather than water quality data, which were instead used to test the index's effectiveness. Testing was based on water quality data collected over a number of seasons and years from 15 drinking water reservoirs in subtropical, southeast Queensland. The index correlated significantly and strongly with algal cell densities, including potentially toxic cyanobacteria, as well as with the proportions of cyanobacteria in summer months. The index also performed better than each of the measures of reservoir and catchment characteristics alone, and as such, was able to encapsulate the physical characteristics of subtropical reservoirs, and their catchments, into an effective indicator of the vulnerability to summer blooms. This was further demonstrated by calculating the index for a new reservoir to be built within the study region. Under planned dimensions and land use, a comparatively high level of vulnerability was reached within a few years. However, the index score and the number of years taken to reach a similar level of vulnerability could be reduced simply by decreasing the percentage of grazing land cover via revegetation within the catchment. With climate change, continued river impoundment and the growing demand for potable water, our index has potential decision making benefits when planning future reservoirs to reduce their vulnerability to cyanobacterial blooms. © 2010 Elsevier Ltd. Source

Leigh C.,Griffith University | Burford M.A.,Griffith University | Roberts D.T.,Queensland Bulk Water Supply Authority Seqwater | Udy J.W.,Queensland Bulk Water Supply Authority Seqwater
Water | Year: 2010

The ability to predict reservoir vulnerability to summer blooms and to detect thresholds of change in phytoplankton cell densities in response to environmental factors would provide information critical for decision making, hazard prevention and management. We used a new method to detect synchronous change points in densities of phytoplankton taxa along the gradient of percentage grazing land cover in catchments, based on data collected from 15 reservoirs in subtropical Australia during summer 2009. In addition, we propose a predictive index of vulnerability that is based on simple measures of reservoir and catchment characteristics, including percentage grazing land cover. Our findings suggest that land use in the catchments of the studied reservoirs has a strong impact on phytoplankton composition and densities, and hence summer bloom phenomena. Source

Rolls R.J.,Griffith University | Ellison T.,Griffith University | Faggotter S.,Griffith University | Roberts D.T.,Queensland Bulk Water Supply Authority Seqwater
Aquatic Conservation: Marine and Freshwater Ecosystems | Year: 2013

Patterns of connectivity are critical to structuring both spatial and temporal variation in the composition of species populations and assemblages. Water resource development has an important impact on longitudinal connectivity in rivers, and disrupts natural patterns of dispersal of individuals between segments of the river network. Consequently, artificial barriers alter the structure, size and distribution of species populations leading to impacts on aquatic biodiversity. Quantitative assessment of the ecological effects of connectivity alteration is necessary to develop effective conservation plans to manage the impacts of anthropogenic fragmentation. Connectivity alteration is a complex environmental disturbance because the potential scale of impact is dependent on the spatial scale at which biota undergo life-history processes such as spawning and recruitment. Few river networks have single migration barriers, meaning that multiple points of fragmentation are present and have potentially interacting effects. Therefore, conventional 'control-impact' approaches to impact assessment may be inappropriate or confounded. Furthermore, monitoring patterns of fish population or assemblage structure moving through fish passage facilities alone creates a mismatch between the spatial scale of impact and assessment of water resource development. This paper uses a case study in subtropical Australia to highlight three potential approaches to increasing inference of the impact of fragmentation by barriers on riverine fish. Thorough understanding of life-history and dispersal ecology of fish is necessary to understand and predict the consequences of fragmentation, and comparing patterns of distribution among species with different migration requirements can identify sources of fragmentation. Monitoring patterns in fish assemblages at both the barrier and river network scale increases the strength of inference of the effects of connectivity alteration and management. Experimental removal of artificial barriers would assist in determining the effect of fragmentation by restoring connectivity. Such approaches would improve predictions of connectivity management and underlying drivers of aquatic biodiversity. © 2013 John Wiley & Sons, Ltd. Source

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