An extensive, seven-year citizen science project in the Macleay River catchment has found toxic metalloids associated with historic mining can endure for hundreds of years, long after mining activity has ceased.
Prompted by community concerns over water quality and mining-related contamination, the study explored the seasonal behaviour of two carcinogenic metals, arsenic and antimony, that often occur together in mining-impacted landscapes.
The project was a collaboration between researchers at Southern Cross University and local community group Save Our Macleay River (SOMR), with about $22,000 in funding from the NSW Department of Climate Change, Energy, the Environment and Water.
Due to the longevity of the project and the commitment of the citizen scientists, it was possible to track these metalloids across a period that included drought, floods and bushfires.
Southern Cross lead researcher Professor Scott Johnston said the picture painted by such an extensive time series provides unique insight into arsenic and antimony in the river and the environmental impacts of historic mining.
"It's a sobering reminder of the importance of taking care of our river systems, and of the potential for long-term effects," he said.
The study involved the collection of more than 500 samples by local residents near Bellbrook in the mid-catchment of the river, located on the NSW mid north coast. The citizen scientists received training in accurate sampling, labelling and storage from Southern Cross experts.
"Arsenic appears to be strongly influenced by water temperature and tends to go up and down with the seasons. Antimony is a bit more dynamic and is heavily influenced by where the rain falls in the catchment.
"The transport of antimony and arsenic down the river, by water and sediment, is also linked to big seasonal climate patterns like the El-Nino-Southern Oscillation," said Professor Johnston.
Although concentrations of antimony were mostly below guideline values, the data indicated it could take 600-1000 years before the river is fully leached back to pre-mining levels.
"During the project we've also been able to track the impact of natural disasters like bushfires, drought and floods on the river," he said.
Founding member of SOMR Mr Arthur Bain is a Kempsey Shire Councillor who was instrumental in the project.
"We wanted to gather data for an accurate picture of water quality, which is essential when we are deciding how to manage the river and issues like the disposal of tailings," he said.
Professor Johnston said the data collection and research would not have been possible without the dedication of citizen scientists like Arthur.
"People care very much about the place where they live and the natural landscape around them. By combining Southern Cross University's scientific capacity and expertise with the sustained efforts of our local communities, we have a very powerful data set."
"We can use this kind of data to predict how the river might behave over time following natural disasters and how we can best protect and manage it in the future," said Professor Johnston.
COVID-19 had an unexpected effect on the project.
"Floods up and down the eastern seaboard in early 2020 were hot on the heels of the catastrophic 2019 bushfires," said Professor Johnston.
"Large fish kills were reported in many rivers, including the upper Macleay. However, many Government-run water quality monitoring programs across NSW were shut down during this period because it coincided with the first COVID lockdown in 2020.
"The dedicated citizen scientists at home in Bellbrook had a mission and time on their hands and were able to collect daily samples of river water during this period. This has given us an unprecedented level of insight into the impact of bushfires on river water quality and how it recovered over time."
Residents reported the river was like a 'cake mix' full of sediment following the bushfires in 2019. Now the science can show exactly what it was made of and how the water recovered over the following months.
See previous story: Megafires and droughts impact water quality.
About the Catchments, Coasts and Communities Cluster
The Catchments, Coasts and Communities Research Impact Cluster at Southern Cross University works with communities to understand local rivers and water systems, how they process nutrients and pollutants and how we can improve their management.
