Tree water use and sensitivity to contaminated mine water

Riverbank, or riparian, vegetation provides many ecosystem benefits that keep creeks healthy, including habitat and food for fish and wildlife, shade to cool water temperatures and roots to stabilise banks. Because groundwater likely meets more than half of the dry season needs of riparian vegetation in the Top End, groundwater contamination here could significantly impact riparian vegetation and associated river health.

Weathering of waste rock from the Ranger uranium mine releases contaminants, including magnesium sulfate. These contaminants are washed out by rain and are predicted to move through the local groundwater towards Magela Creek. Depending on the concentration, magnesium sulfate (a salt) has the potential to affect the trees, other plants and ecosystems along riverbanks downstream from the Ranger mine site.

The Ranger uranium mine is due to cease operations in 2021 and be revegetated by 2026. This study is leading to better knowledge of common riparian woody species’ groundwater uptake, and therefore their relative dependence on it, to help predict contaminant impacts and inform mine closure and monitoring. The project is also increasing our understanding of the sensitivity of riparian and forest ecosystems to changes in groundwater levels, which can then be applied to changes caused by other factors such as irrigated agriculture developments or climate change. The work is improving our understanding of surface water–groundwater interactions in similar environments.

This project is:

  • identifying where the trees along the creeks in the Magela catchment get their water from – from the soil, from the creek itself or from the shallow groundwater – and the relative quantities of each
  • assessing how sensitive common tree species are to magnesium sulfate levels
  • assessing risks to riparian vegetation from the contaminated water, predict its impact and identify where ongoing monitoring should be focused
  • identifying which tree species grow best in salty areas if rehabilitation is needed

Project activities

  • Compare the isotope signature of trees in the catchment to the isotope signatures of soil, creek, and shallow and deep groundwater to determine the age and source of water that the trees use and their relative dependence on groundwater over a wet–dry cycle
  • Estimate the water use of riparian vegetation through calibrating remotely sensed images
  • Assess the sensitivity of common riparian woody species to magnesium sulfate using greenhouse-based trials
  • Quantify risks to riparian vegetation associated with the discharge of mine-related contaminants into surface and groundwater through analysis and surface and groundwater modelling.

Anticipated outputs

  • Technical reports and associated scientific papers
  • Recommendations for monitoring riparian health
  • Maps of areas that mine-related contaminants are likely to most affect.
  • Communication products for policy-makers, ecological restoration consultants and for the mining and agricultural industries.

Project update April 2020

Tree water use and sensitivity - project update front cover

 

 

 

 

 

 

 

 

 

 

 

 

 

Effect of elevated magnesium sulfate on two riparian tree species potentially impacted by mine site contamination. Scientific Reports 10, 2880. https://doi.org/10.1038/s41598-020-59390-9

Data available at https://doi.org/10.26182/5e61d3ad6a460

Fieldwork is taking place at the Ranger uranium mine as well as upstream and downstream of the mine area.

Ranger map

Magela Creek

This project is being led by Professor Lindsay Hutley from Charles Darwin University (CDU). Professor Hutley is being assisted by researchers from CDU, The University of Western Australia and the Supervising Scientist Branch of the Department of Agriculture, Water and the Environment.

This project is due for completion in June 2021.

Contact

Lindsay Hutley, Charles Darwin University

[email protected]

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  • An upstream monitoring site in Magela Creek, Kakadu. Photo: Supervising Scientist Branch (Commonwealth of Australia).
  • Shadehouse experiment to assess the possible effects of magnesium sulfate on riparian species in the Magela system
  • Glasshouse trial set up at UWA. Photo Fi Freestone.
  • Project team assessing Magela Creek riparian vegetation. Photo NESP Northern Hub.
  • Project team working in Magela Creek. Photo NESP Northern Hub.
  • Gulungul creek floodplain between Baralil and Magela. Photo: Supervising Scientist Branch (Commonwealth of Australia).
  • For extended periods of the year, riparian vegetation relies on groundwater. Photo: Michael Douglas
  • Kakadu National Park surrounds the Ranger Uranium Mine, so effective rehabilitation is essential. Photo: Michael Douglas