Murray Darling Basin Rivers Research Articles

Contribution of invasive carp (Cyprinus carpio) to fish biomass in rivers of the Murray–Darling Basin, Australia

Following the introduction of the ‘Boolarra’ strain to Australia in the mid 1960’s, Common carp (Cyprinus carpio) rapidly spread in waterways across the Murray–Darling Basin (MDB) in southern-eastern Australia. A previous study of the population expansion based upon data up to the early 2000s suggested the carp population may have reached, and was fluctuating around, the ecosystem carrying capacity. It has been widely stated in the scientific literature and media that carp comprise up to 90% of fish biomass in MDB rivers; however, this figure is largely based on sparse data collected in the 1990s and the accuracy of this estimate is uncertain. Here, we analyse three decades (1994–2023) of electrofishing data to estimate the median proportion of total fish biomass contributed by carp across > 1,400 sites in lowland rivers (< 700 m elevation) of the New South Wales (NSW) portion of the MDB. The proportion of sites with fish biomass dominated (> 90%) by carp has declined from ≈ 33% of sites in the mid-1990s to ≈ 20% of sites. The proportion of biomass comprised by carp varied depending on the scale of analysis. Across the NSW MDB, carp accounted for a median of 57% (95% CI: 42.5–70.4) of fish biomass at the site level. At the river catchment scale estimates ranged from ≈ 45–66%. In contrast, the median proportion of carp within key rivers ranged from ≈ 46–80%, suggesting that carp can dominate total fish biomass in some rivers for short time-periods. The proportion of biomass contributed by carp at the NSW MDB scale was remarkably stable across decades, suggesting that the carrying capacity of carp may have been reached. Our revised estimates of the contribution of carp to overall fish biomass can facilitate informed debate around the dominance of carp in MDB rivers and provide important information for carp management in the future.

Central Pacific El Niño as a Precursor to Summer Drought‐Breaking Rainfall Over Southeastern Australia

AbstractUsing an extended 120‐year record of El Niño events, we distinguish between central Pacific (CP) and eastern Pacific (EP) types to show that the strength of CP events is a factor in the amplitude and sign of the impact on rainfall over southeastern Australia. Both weak and strong CP events cause widespread rainfall deficits in Australia during the onset phase from April to September. However, this relationship reverses over southeastern Australia including the Murray Darling Basin river catchment region for the strongest CP events after October, leading to positive rainfall anomalies during the mature phase of strong CP El Niños. This reversal can be explained by a change in the circulation over eastern Australia from drier, more westerly orientated flow to moister, more easterly onshore flow. These findings may help with seasonal prediction efforts to predict drought‐breaking rain such as occurred in early 2020.

News media framing of the Murray–Darling Basin ‘water theft’ controversy

An Australian Broadcasting Corporation (ABC) Four Corners investigation, screened on free-to-air television on 24 July 2017, revealed a series of improper conducts pertaining to the Murray–Darling Basin river system. The journalistic exposé included allegations of water theft, questionable compliance decisions and collusion between water regulators and irrigation lobbyists. This interdisciplinary study explores the revelations and their framing in a sample of state and national media reports about the ‘water theft’ controversy and its fallout. It compares these with the normative frames adopted by critical green criminology, which views the allegations at the heart of the Murray–Darling Basin controversy in terms of state-corporate interests, industry capture of regulators and the notion that water ‘theft’ constitutes a ‘crime’ because of the environmental harm that results from excessive water extraction. This article presents the findings of the study, which elaborate on the impacts of media framing of crimes of the powerful (such as large agricultural companies and state government agencies), including the shaping of public understandings of environmental matters.

Preferential Riverine Export of Fine Volcanogenic Particles to the Southeast Australian Margin

We report on rare earth element and neodymium isotopic compositions in a series of grain-size fractions separated from river suspended matter in the Murray-Darling Basin (MDB) and a nearby marine sediment core (MD03-2607) offshore south-eastern Australia. This source-to-sink approach was used to further investigate the extent to which sediment sorting may control the geochemistry of suspended loads in rivers, and to provide constraints on the source of the detrital sediment material exported to the ocean. Our results provide further compelling evidence that significant size-dependent geochemical decoupling can occur in river systems, accounting here for Nd isotopic (Nd) differences of up to 8 epsilon-units between silt (>25µm) and colloidal (0.2-0.006 µm; 0.006-0.003 µm) fractions. All suspended particulate samples from the River Murray watershed display a trend towards more radiogenic (higher Nd) Nd signatures with decreasing grain-size, in addition to differing REE signatures, which collectively point towards a preferential volcanogenic origin for the fine-grained inorganic particles transported by MDB rivers. Furthermore, we show that the same river-borne volcanogenic material dominates in the fine-grained detrital fractions extracted from core MD03-2607 at the south-eastern Australian margin; a finding corroborated by REE signatures in a series of copepod faecal pellet separates from the same core. Collectively, our results suggest that river sediment discharge is accompanied by preferential export of fine-grained volcanogenic particles to the ocean. This potential source of bioavailable trace metals and nutrients in ocean surface waters could impact marine productivity.

The Benefits of Community and Stakeholder Driven Fish Monitoring Projects in a Murray-Darling Basin River

The Benefits of Community and Stakeholder Driven Fish Monitoring Projects in a Murray-Darling Basin River

Size, growth and mortality of riverine golden perch (Macquaria ambigua) across a latitudinal gradient

Effective fisheries management requires fish size, growth and mortality information representative of the population and location of interest. Golden perch Macquaria ambigua is long lived, potamodromous and widespread in the Murray–Darling Basin (MDB), Australia. Using a sample spanning 13 river systems and 10° of latitude, we examined whether the maximum size of golden perch differed by latitude and whether growth and mortality varied between northern and southern MDB regions. The length, weight and age ranges of golden perch sampled (n=873) were 52–559mm, 2–3201g and 0+ to 26+ years respectively, and maximum length and weight were unaffected by latitude. Length and age–length distributions represented by age–length keys varied by region, with greater variability in age-at-length and a larger proportion of smaller individuals in northern MDB rivers, which generally exhibit greater variability in discharge. Growth and mortality rates were similar between regions, and an MDB-wide von Bertalanffy growth model (L∞=447, k=0.32 and t0=–0.51) and instantaneous mortality rate (Z=0.20) best described the data. An MDB-wide length–weight equation also provided the best fit (W=6.76×10–6 L3.12). Our data suggest that the MDB can be treated as one management unit in terms of golden perch maximum size, growth and mortality parameters.

Palaeohydrology of lowland rivers in the Murray-Darling Basin, Australia

This study derives a new function describing the relationship of channel bankfull discharge (Qbf) to channel width in modern rivers of the Murray-Darling Basin (MDB) of southeastern Australia and applies this to dated palaeochannels of seven rivers to quantify late Quaternary discharge history in this important basin. All rivers show high MIS3 and MIS2 Qbf, declining in the Holocene. The Qbf of modern MDB rivers is correlated with total catchment precipitation but comparison with palaeochannel Qbf estimates shows that while enhanced runoff efficiency is necessary to account for much larger late Pleistocene palaeochannels, either lower or higher precipitation rates could have prevailed. A strong association between relative palaeo- Qbf enhancement and temperature suggests a temperature-mediated mechanism controlling river discharge, such as the fraction of precipitation stored as snow and thawing in spring, the enhancement of orographic rainfall, or CO2 feedbacks with vegetation cover. Significantly enhanced MIS3 Qbf requires an additional mechanism, such as increased rainfall. These findings are consistent with others that increased moisture availability was associated with past colder climates, although this was not necessarily the result of enhanced precipitation.

An integrated modelling framework for building a daily river system model for the Murray–Darling Basin, Australia

ABSTRACTThe Murray–Darling Basin (MDB) is home to two million people and accounts for about 60% of the water use in Australia. The MDB river system is a highly complex and mostly regulated system covering four states (Queensland, New South Wales, Victoria and South Australia) and one territory. Different jurisdictions used different models for water resources and planning. A number of difficulties were faced in combining those models (of different characteristics and spatio-temporal resolutions) for basin-wide water resources planning. In order to overcome those difficulties and enhance the consistency and transparency in modelling outcomes across multiple jurisdictions, this paper proposes a homogeneous agent-based integrated modelling framework. Each agent is used to represent a region in the MDB. Its behaviour is modelled by a newly built Source river model. The interactions between agents are modelled based on the hydrological connectivity in the real-world river systems. A three-level parallel computing mechanism is developed to significantly increase its efficiency and reduce computational time. Due to its homogeneousness, it largely reduces the system complexity and makes modelling results consistent, explainable and comparable. By nature, the agent-based system is flexible and portable. All these unique features of the platform suit the modelling needs of various states to federal government water resource management agencies.

The evolution and performance of river basin management in the Murray-Darling Basin

We explore bioregional management in the Murray-Darling Basin (MDB) in Australia through the institutional design characteristics of the MDB River Basin Organization (RBO), the actors and organizations who supported and resisted the establishment of the RBO, and the effectiveness of the RBO. During the last 25 years, there has been a major structural reform in the MDB RBO, which has changed from an interstate coordinating body to an Australian government agency. Responsibility for basin management has been centralized under the leadership of the Australian government, and a comprehensive integrated Basin plan has been adopted. The driving forces for this centralization include national policy to restore river basins to sustainable levels of extraction, state government difficulties in reversing overallocation of water entitlements, the millennium drought and its effects, political expediency on the part of the Australian government and state governments, and a major injection of Australian government funding. The increasing hierarchy and centralization of the MDB RBO does not follow a general trend toward multilevel participative governance of RBOs, but decentralization should not be overstated because of the special circumstances at the time of the centralization and the continuing existence of some decentralized elements, such as catchment water plans, land use planning, and water quality. Further swings in the centralization–decentralization pendulum could occur. The MDB reform has succeeded in rebalancing Basin water allocations, including an allocation for the environment and reduced diversion limits. There are some longer term risks to the implementation of reform, including lack of cooperation by state governments, vertical coordination difficulties, and perceived reductions in the accountability and legitimacy of reform at the local level. If implementation of the Basin plan is diverted or delayed, a new institution, the Commonwealth Environmental Water Holder, can play a major role in securing and coordinating environmental water supplies.

Managing people, water, food and fish in the Murray–Darling Basin, south‐eastern Australia

AbstractThe Murray–Darling Basin (MDB) covers 1.1 million km2, involves six legislative jurisdictions, a myriad of different agencies and illustrates the many complexities of managing fishes, people and water. Its rivers provide water for agriculture, are highly regulated and generally in poor health. Water allocation reform is underway to improve ecological condition but provision of water for environmental outcomes competes with agricultural requirements. Murray–Darling Basin rivers and fishes are important culturally and contribute substantially to tourism and recreational fishing. The MDB has a low number of fish species, now estimated to be at 10% of their pre‐European abundance, and all subject to a range of threats, many related to water use and associated infrastructure. The MDB Native Fish Strategy takes a coordinated, long‐term, whole‐of‐fish‐community approach to address priority threats and rehabilitate populations. This strategy provides a holistic approach with many actions that complement the potential benefits of water reform.

Field assessment of surface water–groundwater connectivity in a semi‐arid river basin (Murray–Darling, Australia)

AbstractIn semi‐arid and arid river basins, understanding the connectivity between rivers and alluvial aquifers is one of the key challenges for the management of groundwater resources. The type of connection present (gaining, losing‐connected, transitional and losing‐disconnected) was assessed at 12 sites along six Murray–Darling Basin river reaches. The assessments were made by measuring the hydraulic head in the riparian zone near the rivers to evaluate if the water tables intersected the riverbeds and by measuring fluid pressure (ψ) in the riverbeds. The rationale for the latter was that ψ will always be greater than or equal to zero under connected conditions (either losing or gaining) and always lesser than or equal to zero under losing‐disconnected conditions. A mixture of losing‐disconnected, losing‐connected and gaining conditions was found among the 12 sites. The losing‐disconnected sites all had a riverbed with a lower hydraulic conductivity than the underlying aquifer, usually in the form of a silty clay or clay unit 0.5–2 m in thickness. The riparian water tables were 6 to 25 m below riverbed level at the losing‐disconnected sites but never lower than 1 m below riverbed level at the losing‐connected ones. The contrast in water table depth between connected and disconnected sites was attributed to the conditions at the time of the study, when a severe regional drought had generated a widespread decline in regional water tables. This decline was apparently compensated near losing‐connected rivers by increased infiltration rates, while the decline could not be compensated at the losing‐disconnected rivers because the infiltration rates were already maximal there. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Zooplankton dynamics in response to the transition from drought to flooding in four Murray–Darling Basin rivers affected by differing levels of flow regulation

Extreme low and high flow periods associated with droughts and floods regularly influence many river systems, yet little is known regarding their role in shaping riverine zooplankton communities. This study investigated zooplankton dynamics in response to the transition from drought to flooding in four southern Murray–Darling Basin rivers managed by different levels of flow regulation. Results indicated that the onset of flooding was associated with an increase in the taxon richness and total transport (abundance) of zooplankton in the unregulated Ovens and Kiewa Rivers, and an increase in the total transport of zooplankton in the mildly regulated Broken River. In comparison, no significant flood effects on zooplankton taxon richness or transport were detected in the highly regulated Murray River. This suggests that the flooding was beneficial for enhancing zooplankton abundance in the Ovens, Kiewa and Broken Rivers, whereas any potential benefits were comparatively short-term and/or reduced in the Murray River. We hypothesise that the relatively short-term and/or reduced response of the zooplankton community to the flooding in the Murray River was probably largely due to the occurrence of a hypoxic blackwater event in suppressing zooplankton emergence.

Unfinished Business: Completing the Mudmap on the Riverbed – The Legal Lacuna in the Tri-State Area of the River Murray

With the approaching centenary of the Victorian-South Australian border litigation, the necessity of restoring and maintaining river flows in the Murray-Darling Basin river system including the equitable allocation of rights to those flows, and the failure of the four states and the Commonwealth to agree on the future co-operative administration of the Basin, the authors offer their resolution of the ‘missing’ border in the tri-state area of Victoria, New South Wales, and South Australia in the locale of Mildura-Wentworth-Renmark where the three states abut. The resolution of the missing border is essential to the proper exercise of spatial or territorial jurisdiction. Although of small consequence for the past 150 years the time is approaching when this issue must be resolved: it is ‘unfinished business’.

Environmental flows, river salinity and biodiversity conservation: managing trade-offs in the Murray - Darling basin

The Murray–Darling basin's river system suffers from over-allocation of water resources to consumptive use and salinity threats to water quality. This paper draws attention to the current state of knowledge and the need for further investigations into the biological effect of river salinity on aquatic biota and ecosystems, the threats of dryland salinity to terrestrial biodiversity, and managing environmental flows and salinity control to limit the trade-offs in water-resource security and river salinity.There is growing evidence that river salt concentrations lower than the normally adopted threshold have sublethal effects on species and ecosystems, over a longer time period. Further knowledge is required.There is no agreed process for incorporating terrestrial biodiversity values at risk into a strategic response for dryland-salinity management. This is a public policy issue to be addressed.Recent studies have quantified the trade-off in surface water flow and river salinity from refforestation and revegetation of upland catchments to control salinity. The potential losses or benefits to environmental values have not been quantified.Such improved knowledge is important to the Murray–Darling basin and relevant to other river basins and catchments in Australia.