Science to inform artifical floodplain inundation: movement and habitat use of Murray cod during testing of the Chowilla Creek regulator
Despite the pervasive impacts of river regulation on riverine ecosystems, further regulation in the form of weirs, levees and pumping is being used to artificially inundate floodplains of the River Murray with an aim to improve floodplain health. Such approaches are unprecedented and contemporary ecological models of riverine ecology and autecology suggest they carry substantial risks. In response to terrestrial floodplain degradation at Chowilla, in the lower River Murray, the Chowilla Creek regulator was constructed with the primary objective of maintaining or improving the condition of floodplain overstorey vegetation. Chowilla also supports regionally significant Murray cod (Maccullochella peelii) populations, in particular providing preferred lotic (flowing water) habitats and promoting recruitment during periods of low-flows and limited recruitment in the main channel of the River Murray.
Operation of the Chowilla Regulator has the potential to alter the hydrodynamics of lotic habitats, interrupt longitudinal connectivity, and decouple riverine and floodplain hydrographs. As such, the regulator poses significant risks to the movement, habitat use, spawning and recruitment of Murray cod. In spring–summer 2014, the Chowilla Regulator was used to artificially raise upstream water levels by 2.7 m, over the spawning season of Murray cod. The over-arching objective of this project was to conduct a one-year investigation of the movement and habitat use of Murray cod in the Chowilla system and adjacent River Murray in association with the initial testing of the Chowilla Creek regulator in spring–early summer 2014. The specific aims were to use an existing remote radio-receiver network and population of radio-tagged Murray cod to:
Over the period of regulator operation (5 September–5 December 2014) radio-tagged Murray cod exhibited high fidelity to core regions in the perennial anabranch habitats of Chowilla and specific regions of the River Murray main channel, and either moved little within these regions or moved between them. Murray cod predominantly occupied habitats characterised by flowing water and large wood, but not ephemeral floodplain habitats. Patterns of movement and habitat use were similar to those previously observed at Chowilla during both low-flow periods and natural flooding. During natural flooding, however, several Murray cod undertook large-scale (>200 km) upstream movements in the River Murray. Similar movements were not observed during low-flows, but during regulator operation, six fish initiated upstream movements that appeared to be aborted when these fish reached the River Murray. Murray cod may have initiated exploratory behaviour in anticipation of a flood, but instead encountered the homogenous habitat of the Lock 6 weir pool. These altered behavioural patterns may have resulted from decoupling of floodplain and riverine hydrology.
Operation of the regulator substantially altered the hydraulic characteristics of key Murray cod reaches and the micro-habitats used by individual fish, particularly in Slaney Creek, the primary Murray cod habitat in Chowilla. During peak regulator operation, mean water velocities in Slaney Creek were approximately 50% of those measured when the regulator was not in place and hydraulic complexity, as measured by strength and frequency of water circulation, was similarly reduced. At a site occupied by Murray cod in Chowilla Creek, mean water velocities and hydraulic complexity varied little between regulator operation and when the regulator was not in place, although discharge in Chowilla Creek was three times greater during regulator operation. Whether decreased habitat quality resulted in increased movement rates as fish searched for alternative habitats, or had an impact on spawning, remains unresolved in this short-term study.
Chowilla Creek provides the primary conduit for the movement of reproductively mature Murray cod between the River Murray and the structurally complex, lotic habitats of Chowilla. Maintenance of connectivity between these habitats is considered fundamental to sustaining the integrity of Murray cod populations in the lower River Murray. During the operation of the Chowilla Regulator, radio tagged Murray cod were delayed or prevented from moving both downstream and upstream past the regulator. Three large (>1 m total length) female fish did pass downstream of the regulator with one attempting unsuccessfully to return upstream. It is uncertain if these fish passed downstream over the weir or through the vertical slot fishway. Fragmentation of longitudinal connectivity is a major risk of the Chowilla regulator and fishways could be effective in partly overcoming this impact. As such, the hydraulic and biological function of the fishways on the Chowilla regulator (and ancillary structures) should be assessed as a matter of priority. In parallel, the efficiency of fishway attraction should be evaluated, potentially using electronic tagging approaches.
Engineered artificial floodplain inundation carries substantial ecological risks and to date, untested benefits; yet the concept has been embraced enthusiastically by natural resource management agencies across the southern MDB. Operation of the Chowilla regulator exacerbates the impacts of river regulation on Murray cod. Therefore, given the conservation status of Murray cod and the regional significance of Chowilla to Murray cod populations in the lower River Murray, mitigating potential impacts of the regulator should be a priority. Preserving the hydraulic characteristics of fluvial habitats and maintaining longitudinal connectivity present two key challenges for operation of the Chowilla regulator. We also advocate that the regulator be operated in synchrony with the riverine hydrograph to limit the potential for anomalous behavioural responses and maximise opportunities for positive outcomes, such as improved larval survival during higher riverine flows.
Operation of a regulator on Chowilla Creek to promote floodplain ecosystem health represents an unparalleled experiment in lowland river restoration. As such, robustly designed monitoring and research is required to elucidate ecological outcomes, mitigate risks, maximise benefits, and provide the essential feedback loops for adaptive management. Whether altered habitat availability, rates of movement and disrupted connectivity impact individual fitness and/or spawning and recruitment, and ultimately population dynamics, remain to be tested. These are fundamental questions for future operation and management of the Chowilla regulator, and other large-scale floodplain regulators proposed for the River Murray Floodplain. For long-lived species such as Murray cod, robustly answering these questions will be a long-term (decadal) proposition.
Chris Wright holds significant experience in public sector senior leadership, having led policy, scientific and operational business units over the last twelve years in both State and Commonwealth government agencies. Chris has excellent experiences in leading policy and strategy formulation. He is skilled in building and maintaining networks across the public and private sectors to facilitate business delivery; leading and negotiating with others to achieve outcomes; and in bridging the science-policy gap, drawing on earlier roles in geospatial information systems (GIS) consulting. Chris’s formal qualifications include a Bachelor of Social Science, a Masters of Spatial Information Science and graduation from the AICD Company Directors course in 2019.
Dr Ilka Wallis is a hydrogeologist with areas of expertise in quantitative hydrogeology and geochemistry. Ilka focuses on the development of reactive geochemical transport models which integrate fundamental processes that are normally studied in isolation (hydrogeological, mineralogical, geochemical and biochemical).
Ilka is also an Adjunct Professor, Department of Civil Engineering, University of Manitoba, Canada since 2017.
Peter Goonan is the Principal Aquatic Biologist in the Environmental Science Branch of the EPA. He has over 30 years’ experience monitoring the condition of aquatic ecosystems in SA and assessing the environmental effects caused by discharges, deposits and contaminants entering inland and coastal waters. He specialises in aquatic invertebrate identification and their responses to contaminants and water quality stressors. He also provides expert professional advice relating to water quality risks, regulation, policy, and strategic directions, and represents the EPA as an expert witness in court.
Dr Paul Monis is a technical expert within SA Water’s Business Services group, which provides scientific expertise to support the delivery of water and wastewater services to SA Water’s customers. He has specialist expertise in the areas of biotechnology and microbiology, with almost 20 years’ experience applying DNA-based and other technologies to address water quality challenges posed by microorganisms, especially enteric pathogens. Dr Monis also holds title of Adjunct Associate Professor at Flinders University, the University of Adelaide and UniSA.
Jennie’s role in the Department for Environment and Water (DEW) allows her to foster and strengthen opportunities for researchers to better connect with government to enable evidence-based decision making. Jennie has extensive experience working in both universities and government, allowing her to bridge the divide between the two sectors. She is focused on connecting natural resource researchers with natural resource decision makers, and facilitating fit for purpose partnerships.
Dr Tanya Doody is a Principal Research Scientist working on high impact spatial eco-hydrological projects within CSIRO’s Land and Water Business Unit. Dr Doody leads the Managing Water Ecosystems Group, based in Adelaide, Albury and Canberra and has significant experience in quantifying the water requirements of vegetation and at times, their impact on water resources. This involves ecophysiological field-based research to underpin remote sensing tools to scale regionally to improve our understanding of the effect of flood regimes on the health of water-dependent ecosystems on the Murray-Darling Basin floodplains. Additional research includes investigating the ecological response of vegetation to water availability and environmental water to inform integrated basin water planning and management.
Professor Lin Crase is Professor of Economics and Dean of Programs (Accounting & Finance) at UniSA. He joined UniSA in February 2016 as Head of School of Commerce. Prior to commencing at UniSA, Lin was Professor and Director of the Centre for Water Policy and Management at La Trobe University.
Lin’s research has focused on applied economics in the context of water. He has analysed water markets and the property rights that attend them, water pricing and numerous applications of water policy. Whilst his expertise includes the Murray-Darling Basin in Australia, he has also worked on projects in south Asia, Japan and Europe. Lin has published over 100 journal articles, numerous book chapters, four books and a range of other papers and opinion pieces.
Justin has broad research interests in limnology and water treatment with a primary focus on coupling between hydrodynamics, biology and water quality contaminants such as cyanobacteria and pathogens. He is a founding member of the management committee of the IWA Specialist Group on Lake and Reservoir Management and member of the Steering Committee for the Global Lakes Ecological Observatory Network.
Justin has a PhD and a Bachelor of Science degree with Honours from the University of Adelaide.
Daniel Flaherty is the Accountant for the Goyder Institute for Water Research.
Daniel has extensive experience in higher education having worked in senior financial management roles at the University of South Australia, Flinders University and the University of Adelaide over the past 26 years. Daniel has also been a Board Director on a number of university related entities. Prior to that, Daniel has worked in a range of agencies in the Commonwealth and State Governments.
Daniel is a Fellow of CPA Australia and has a Bachelor of Economics from the University of Adelaide.
Alec Rolston joined the Institute in 2021 as Research Program Manager of the Goyder Institute’s research projects in the Healthy Coorong, Healthy Basin program. He has extensive experience in integrated water resource management, integrated catchment management, drinking water source protection and wetland ecology, conservation and management across Europe and Australia.
Alec holds a PhD from the National University of Ireland Maynooth and has worked with An Fóram Uisce|The Water Forum and the Dundalk Institute of Technology in Ireland as well as the MANTEL Innovative Training Network across Europe.
Alec spent his early career in Adelaide working with Flinders University through the Coorong, Lower Lakes and Murray Mouth (CLLAMM) Ecology Research Cluster and within the Department for Environment and Water.
Daniel Pierce has managed research projects at the Goyder Institute for Water Research since November 2017 under both the second and third terms of the Institute.
Daniel brings experience in project management and knowledge transfer and application from 4 years working as a Senior Hydrogeologist in the Department for Environment and Water (DEW) in South Australia and from 13 years of private sector work in environmental management, science and engineering in Australia and the South Pacific. His work with DEW has included providing technical advice to the development and revision of Water Allocation Plans around South Australia in collaboration with researchers and policy makers, and managing a team of groundwater modellers and hydrogeologists involved in an assortment of water resource management issues.
Daniel has a Bachelor of Engineering (Hons, Environmental) and a Bachelor of Science (Geography) from the University of Western Australia.
Professor Lombi’s main contributions to environmental research cover various aspects of contaminant risk assessment, biogeochemistry, ecotoxicology and waste management. Furthermore, the methodological development he has pursued in his research has provided the basis for collaborative efforts in a variety of research areas ranging from soil fertility and plant physiology to human health issues related to contaminant uptake via occupational exposure and diet. In the last few years he has been increasingly focusing on the transformation and toxicity of manufactured nanomaterials in the environment.
Dr Carmel Pollino is a Research Director for Land and Water at CSIRO. She has 20 years of experience working on water issues in Australia and throughout Asia. Carmel has degrees in science and environmental law and works across the science and policy interface. Significant areas of research in Environmental Flows, Hydrology, Ecology and Integrated River Basin Planning. Carmel is the lead and also a contributor to global working groups on water and has published widely in this domain.
Professor Bronwyn Gillanders is interim Head of School of Biological Sciences at the University of Adelaide. Prof Gillanders completed her BSc at the University of Canterbury, MSc at the University of Otago and her PhD at the University of Sydney. She has a research background in environmental science focused predominantly on freshwater and marine ecology.
Her research interests include integrated marine management; coastal carbon opportunities; multiple use activities and cumulative impact assessment; biology, ecology and fisheries of cephalopods; stocking and provenance of fish; plastics in the marine environment including in seafood; use of fish bones (and other calcified structures) for assessing ecological and environmental change. She has trained and mentored ~70 Honours and Higher Degree Research students and shaped the future of 1000s of students through her undergraduate teaching. She is passionate about encouraging capable women to enter and remain in science careers.
Dan Jordan is the Director, Water Security, Policy and Planning, Department for Environment and Water (DEW). Dan is also the Basin Officials Committee Alternate Member for South Australia.
Professor Okke Batelaan is a graduate of the Free University of Amsterdam, Netherlands (MSc – Hydrogeology) and of the Free University Brussels, Belgium (PhD – Engineering). He worked for more than 20 years at the Free University Brussels and also led the hydrogeology group at the KU Leuven, Belgium since 2006. He was chairman of the Interuniversity Programme in Water Resources Engineering.
Since 2012 Okke Batelaan is Strategic Professor in Hydrogeology and currently Dean of the School of the Environment, Flinders University. Okke has broad experience in teaching groundwater hydrology, groundwater modelling, GIS and remote sensing for hydrological applications. He was supervisor of more than 140 MSc and 25 PhD students. He has extensive research experience and a publication record in shallow groundwater hydrology and modeling, recharge-discharge estimation and modeling, urban hydrology and distributed modelling, ecohydrology and impacts of land use and climate change on groundwater systems. He coordinated and participated in a large number of projects in Europe, Africa, South America, Asia and Australia. He is editor-in-chief of Journal of Hydrology: Regional Studies and of MDPI-Hydrology.