Management of the River Murray is becoming more complex as new infrastructure is being constructed to inundate floodplains and improve their health. However, this may carry water quality or ecological risks if it’s not used effectively. To date, most research has focused on how inundation benefits floodplain communities, but changes within the channel are not as well understood.
The Goyder Institute for Water project, Ecological connectivity of the River Murray: managing ecological outcomes and water quality risks through integrated river management, is filling some key knowledge gaps. It is developing knowledge and models that will help environmental water managers to assess the risks and benefits of manipulating river flows and floodplain inundation. Dr Matt Gibbs (Department for Water and Environment) and Professor Justin Brookes (The University of Adelaide) lead the project and are supported by colleagues from CSIRO, SARDI and DEW. The team will use two years of field and laboratory investigations to quantify relationships between the hydraulics of the river and water quality risks and ecological responses.
The team are currently in their second year of data collection, with field work focused on the Chowilla anabranch. Data analysis from a successful first year of field work is showing promising relationships between river velocity and the drift and retention of Murray Cod larvae as well as the abundance of zooplankton – a critical food source for fish. The team have also enhanced the ability to determine the risk of hypoxic blackwater events by quantifying the amount of organic matter that accumulates on the floodplain for different tree species under different conditions. They’ve also begun testing the blackwater model against historical data at Chowilla before expanding the model to the rest of the South Australian floodplain.
The team are also researching the dissolved oxygen dynamics of the system and have completed a model that will allow the impact of different management scenarios on dissolved oxygen levels to be tested. Stable isotope data is also being used to understand how carbon (i.e. energy) and nutrient flows through the food-web. To do this, the first year’s data has been analysed and the team are currently testing a modelling approach.
Collating and analysing historical data is also an important part of the project. Cyanobacterial abundance records from 1947–present have been collated and are being used to identify the flow conditions that increase cyanobacterial abundance, for both harmful (e.g. blue green algae) and beneficial phytoplankton species. Historical Murray cod larval, zooplankton and plant seed data has also been collated and is being used to develop preliminary conceptual models of hydro-ecological relationships.
The research project draws directly from the results of two DEW projects: Source Modelling to Support SARFIIP Environmental Pathways – a refined source model representing weirs and floodplain infrastructure; and Pike Blackwater Stage 3, which provides improvements and testing of the source blackwater model. The research team are also collaborating with the Commonwealth Environmental Water Office’s Long Term Intervention Monitoring Project, which is comparing and contrasting approaches to using hydraulic models to evaluate ecological responses within the Murray Darling Basin.
The project team are making good progress on integrating all of this information into a predictive tool to assess the trade-offs of manipulating river and floodplain flows. On completion, environmental managers will be able to use this tool to assess the ecological risks and benefits at multiple sites of various river management scenarios.