School of Agriculture, Food and Ecosystem Sciences - Research Publications
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ItemNo Preview AvailableSmall artificial impoundments have big implications for hydrology and freshwater biodiversity(WILEY, 2022-04)Headwater streams are critical for freshwater ecosystems. Global and continental studies consistently show major dams as dominant sources of hydrological stress threatening biodiversity in the world’s major rivers, but cumulative impacts from small artificial impoundments (SAIs) concentrated in headwater streams have rarely been acknowledged. Using the Murray Darling River basin (Australia) and the Arkansas River basin (US) as case studies, we examined the hydrological impacts of SAIs. The extent of their influence is considerable, altering hydrology in 280–380% more waterways as compared to major dams. Hydrological impacts are concentrated in smaller streams (catchment area <100 km2), raising concerns that the often diverse and highly endemic biota found in these systems may be under threat. Adjusting existing biodiversity planning and management approaches to address the cumulative effects of many small and widely distributed artificial impoundments presents a rapidly emerging challenge for ecologically sustainable water management.
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ItemUsing State-and-Transition Simulation Models (STSMs) to Explore Dynamic Population Responses to Drought Cycles in Freshwater Ecosystems(FRONTIERS MEDIA SA, 2022-08-22)Climate variability and change pose significant threats to aquatic biodiversity, particularly in areas with low and variable streamflow. Quantifying the magnitude of risk from these threats is made more difficult by the variable responses of individual species to hydrologic stress. Patterns of population decline and recovery in response to drought cycles will depend on both the resistance traits (e.g., tolerance to harsh environmental conditions) and resilience traits (e.g., fecundity, age at maturity), both of which vary considerably among species. Collectively these traits can give rise to varied, and lagged patterns of decline and recovery in response to hydrologic variability, which ultimately can affect population viability in drought prone environments and in response to a changing climate. Such population cycles are typically modelled based on demographic rates (mortality and recruitment) under different climate conditions. However, such models are relatively data intensive, limiting their widespread development. A less precise but more tractable approach is to adopt state-and-transition approaches based on semi-quantitative population states (or population size estimates), and modelled transitions between states under different hydrologic conditions. Here we demonstrate the application of such models to a suite of diverse taxa, based on an expert elicitation of expected state-changes across those different taxa under a range of different flow conditions. The model results broadly conform with population changes observed in response to a major drought in the case-study system, mimicking the observed lags in recovery of species with different life-histories. Stochastic simulations of population cycles under scenarios of more protracted drought provide a semi-quantitative measure of the potential risk to different species under each scenario, as well as highlighting the large uncertainties that can arise when taking into account stochastic (rather than deterministic) state-transitions.
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ItemCommunity-powered urban stream restoration: A vision for sustainable and resilient urban ecosystems(The University of Chicago Press, 2022-09-01)Urban streams can provide amenities to people living in cities, but those benefits are reduced when streams become degraded, potentially even causing harm (disease, toxic compounds, etc.). Governments and institutions invest resources to improve the values and services provided by urban streams; however, the conception, development, and implementation of such projects may not include meaningful involvement of community members and other stakeholders. Consequently, project objectives may be misaligned with community desires and needs, and projects may fail to achieve their goals. In February 2020, the 5th Symposium on Urbanization and Stream Ecology, an interdisciplinary meeting held every 3 to 5 y, met in Austin, Texas, USA, to explore new approaches to urban stream projects, including ways to maximize the full range of potential benefits by better integrating community members into project identification and decision making. The symposium included in-depth discussion about 4 nearby field case studies, participation of multidisciplinary urban stream experts from 5 continents, and input from the Austin community. Institutional barriers to community inclusion were identified and analyzed using real-world examples, both from the case studies and from the literature, which clarified disparities in power, equity, and values. Outcomes of the symposium have been aggregated into a vision that challenges the present institutional approach to urban stream management and a set of strategies to systematically address these barriers to improve restoration solutions. Integrating community members and other stakeholders throughout the urban restoration process, and a transparent decision-making process to resolve divergent objectives, can help identify appropriate goals for realizing both the ecological and social benefits of stream restoration.
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ItemFragmentation of lateral connectivity and fish population dynamics in large rivers(Wiley, 2022-05-01)Abstract Lateral Hydrological Connectivity (LHC) has been extensively fragmented in river–floodplain ecosystems of the world. Uncertainties about how LHC affects fishes are great, impeding the design of effective rehabilitation strategies. Existing conceptual frameworks do not provide sufficient mechanistic detail to support the novel decision problems river managers face. We offer a framework of how LHC affects fishes in river–floodplain ecosystems that is, process‐based, integrates all life‐stages and is spatial; these features, we argue, are required to assess risks and opportunities associated with different LHC rehabilitation strategies. Within river–floodplain segments, LHC affects population processes through five ‘effect‐classes’: effects of floodplain habitat (1) and channel habitat (2); effects of material subsidies from the floodplain to the channel (3) andvice versa(4); and effects of connectivity on lateral dispersal (5). The relative influence of these effect‐classes on processes varies among species and life‐stages. At the scale of the drainage basin, inter‐segment variation in geomorphology generates a longitudinal source‐sink structure to habitat quality and quantity, pointing to a need to better understand fish metapopulation dynamics in river–floodplain ecosystems. Given the significant investment in trying to restore river–floodplain ecosystems, we highlight potentially costly and ineffective LHC management decisions. These include certain heavily engineered LHC rehabilitation strategies that do not promote critical population processes at a local scale, and at basin scales implementing strategies that do not facilitate the metapopulation processes that promote species’ persistence.
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ItemThe politicisation of science in the Murray-Darling Basin, Australia: discussion of 'Scientific integrity, public policy and water governance'(Taylor & Francis, 2021-10-30)Many water scientists aim for their work to inform water policy and management, and in pursuit of this objective, they often work alongside government water agencies to ensure their research is relevant, timely and communicated effectively. A paper in this issue, examining 'Science integrity, public policy and water governance in the Murray-Darling Basin, Australia’, suggests that a large group of scientists, who work on water management in the Murray-Darling Basin (MDB) including the Basin Plan, have been subject to possible ‘administrative capture'. Specifically, it is suggested that they have advocated for policies favoured by government agencies with the objective of gaining personal benefit, such as increased research funding. We examine evidence for this claim and conclude that it is not justified. The efforts of scientists working alongside government water agencies appear to have been misinterpreted as possible administrative capture. Although unsubstantiated, this claim does indicate that the science used in basin water planning is increasingly caught up in the politics of water management. We suggest actions to improve science-policy engagement in basin planning, to promote constructive debate over contested views and avoid the over-politicisation of basin science.
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ItemPrediction of Hydrologic Characteristics for Ungauged Catchments to Support Hydroecological Modeling(AMER GEOPHYSICAL UNION, 2017-11)Abstract Hydrologic variability is a fundamental driver of ecological processes and species distribution patterns within river systems, yet the paucity of gauges in many catchments means that streamflow data are often unavailable for ecological survey sites. Filling this data gap is an important challenge in hydroecological research. To address this gap, we first test the ability to spatially extrapolate hydrologic metrics calculated from gauged streamflow data to ungauged sites as a function of stream distance and catchment area. Second, we examine the ability of statistical models to predict flow regime metrics based on climate and catchment physiographic variables. Our assessment focused on Australia's largest catchment, the Murray‐Darling Basin (MDB). We found that hydrologic metrics were predictable only between sites within ∼25 km of one another. Beyond this, correlations between sites declined quickly. We found less than 40% of fish survey sites from a recent basin‐wide monitoring program (n = 777 sites) to fall within this 25 km range, thereby greatly limiting the ability to utilize gauge data for direct spatial transposition of hydrologic metrics to biological survey sites. In contrast, statistical model‐based transposition proved effective in predicting ecologically relevant aspects of the flow regime (including metrics describing central tendency, high‐ and low‐flows intermittency, seasonality, and variability) across the entire gauge network (median R2 ∼ 0.54, range 0.39–0.94). Modeled hydrologic metrics thus offer a useful alternative to empirical data when examining biological survey data from ungauged sites. More widespread use of these statistical tools and modeled metrics could expand our understanding of flow‐ecology relationships.
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ItemRegional-scale extremes in river discharge and localised spawning stock abundance influence recruitment dynamics of a threatened freshwater fish(WILEY, 2017-09)Abstract Highly variable recruitment is common for many riverine fish species, governed by a wide range of biotic and abiotic drivers that operate at local and regional scales. The dynamics and drivers of recruitment for many Australian freshwater fish species, particularly those that are rare and long‐lived, are relatively undescribed. This study describes the recruitment dynamics of an endangered riverine fish, Macquarie perch Macquaria australasica, across 5 isolated populations from southeastern Australia, and relates these dynamics to drivers that vary at local and regional scales. We hypothesised large flow events occurring during the core egg, and larval period would be negatively associated with recruitment strength and that recruitment patterns across populations would fluctuate in synchrony in response to extremes in river discharge resulting from regional‐scale climatic patterns. Discharge during the core egg and larval period, which was highly correlated across the region, and a local‐scale variable, spawning stock abundance, were the covariates most important in explaining recruitment strength. We also observed synchronised patterns in recruitment across our populations, thus conforming to predictions of the Moran effect (environmental synchrony). The findings suggest that most remnant populations of Macquarie perch, which are now predominantly isolated within small tributary systems characterised by highly variable flows, face a heightened risk of poor recruitment periods, particularly under climate change predictions. The synchronised patterns in recruitment suggest that threatened freshwater fishes such as Macquarie perch with highly fragmented isolated populations have an increased risk of the regional population becoming imperilled, thus the need for a coordinated multijurisdictional conservation approach.
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ItemSpecies distributions represent intraspecific genetic diversity of freshwater fish in conservation assessments(WILEY, 2016-10)Summary Accounting for genetic diversity and evolutionary processes has long been recognised as an important goal in conservation planning. However, because genetic data are often lacking, surrogate approaches are widely used. Few studies have, however, assessed the capacity of surrogate data, such as higher taxonomic levels (e.g. species distributions) to portray intraspecific genetic diversity. Here, we contrast conservation plans based on traditional species distribution data, with those derived from intraspecific genetic data for a smaller subset of species, both using freshwater fish in northern Australia. We modelled the spatial distribution of 46 species and intraspecific genetic diversity within four common species. We then identified priority areas for conservation using both data sets and evaluated the extent to which solutions obtained from species distribution data portrayed genetic diversity. We found that genetic diversity could be adequately represented within priority areas identified using species distribution data, even at low conservation targets and for species with complex genetic structure. However, this was only true when using the entire fish community (i.e. all 46 species). In contrast, a substantial component of the genetic structure would not be represented in conservation priority areas when using a subset of species. Our results have important implications for the use of surrogates for genetic diversity in conservation planning. Sufficient genetic diversity might be represented in conservation priority areas by including a broad range of species with distributions ranging from common to rare elements in the community in the prioritisation analyses. We recommend focusing on improving accuracy of data on species distributions to reduce uncertainties in conservation recommendations derived from commission and omission errors, to avoid misuse of limited conservation funds and potential failure of conservation practice.
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ItemGo with the flow: the movement behaviour of fish from isolated waterhole refugia during connecting flow events in an intermittent dryland river(WILEY, 2016-08)Summary In many intermittent, dryland rivers, fish are confined to isolated waterholes for much of the year. It is only during brief flow events, which typify the hydrology of these systems, that fish are able to move between waterholes and explore surrounding habitat. Because most of the river channel will dry afterwards, there is a strong advantage for selection of persistent waterholes. Two hundred and fifteen individual fish of three common large‐bodied species were tagged in two isolated waterholes in the Moonie River (Queensland, Australia) over 3 years. Their movements were monitored to identify the flow events that trigger fish movement between waterholes, differences in response among species and size classes and refuge selection preferences. Some individuals of all species moved during flow events and others remained within the same waterhole. There was no clear upstream or downstream preference, and most individuals used a reach of up to 20 km, although some individuals ranged over more than 70 km in only several days. Above a threshold flow of 2 m above commence‐to‐flow level, timing of flow was more important than magnitude, with most movement occurring in response to the first post‐winter flow event, independent of its magnitude and duration. Many of the fish that moved displayed philopatry and subsequently returned to their starting waterhole either by the end of a flow event or on subsequent events, suggesting ability to navigate and a preference for more permanent refuge pools. Maximising survival in a highly variable environment provides a plausible mechanism for maintaining these behaviours. Modifications to both flow regime and hydrological connectivity may reduce movement opportunities for fish in intermittent rivers. Our findings show that fish in intermittent systems use networks of waterholes and that management and conservation strategies should aim to maintain movement opportunities at large spatial scales to preserve population resilience.
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ItemAssessment of the causes and solutions to the significant 2018-19 fish deaths in the Lower Darling River, New South Wales, Australia(CSIRO Publishing, 2022-01-01)In late 2018 to early 2019, three significant fish death events occurred in the Lower Darling River, Australia, with mortality estimates of millions of fish. We examined the proximate and ultimate causes of these events. We determined that not only were the conditions existing at the time a significant contributing factor, but that antecedent conditions, particularly during the period 2010–17, also contributed. The extreme hot and dry climate during 2018, extending into 2019, shaped the conditions that saw a large fish biomass, which had flourished in the Darling River and Menindee Lakes since favourable spawning conditions in 2016, isolated in weir pools, with no means of escaping upstream or downstream. Strong and persistent weir pool stratification created hypoxic conditions in the hypolimnion. A series of sudden cool changes subsequently initiated rapid and sudden mixing of the stratified waters, causing depletion of oxygen throughout the water column and resulting in the fish deaths. The events were also shaped by broader climatic, hydrological and basin management contexts that placed the Lower Darling River at risk of such fish deaths. Our observations have implications for future river management, and we make several suggestions how policy makers and river operators can minimise fish death risks into the future.