In a bid to reduce fertiliser pollution entering the oldest New South Wales marine park, Australia’s biggest blueberry farming region has trialled an emerging innovation that was pioneered to protect Queensland’s Great Barrier Reef.
- Water quality studies across the region have been above guidelines set out by the Australian and New Zealand Environment Conservation Council
- Bioreactor trials on the Coffs Coast are showing promising results and better managing fertiliser runoff into waterways and marine parks
- Researchers hope to conduct further trials
In recent years, researchers found high amounts of nitrogen from fertilisers in Coffs Coast waterways, particularly in the Hearnes Lake catchment, where most horticulture farming occurs.
Southern Cross University PhD candidate Shane White and his team estimated the catchment’s nitrogen levels were six times higher than the Australian east coast average.
High nitrogen and nutrient levels in waterways can have devastating environmental impacts, including algal blooms, which lead to fish kills.
After rainfall events, the nitrogen levels in the Hearnes Lake catchment were at least 50 times higher than recommended under water-quality guidelines set by the Australian and New Zealand Environment Conservation Council (ANZECC).
The catchment’s waterways flow into the Solitary Islands Marine Park, which is home to hundreds of species of fish and dozens of types of coral.
To reduce fertiliser run-off, researchers have been trialling a system called a bioreactor, which has been in use in Queensland to prevent run-off affecting the Great Barrier Reef.
What is a bioreactor?
A bioreactor is a simple trench, filled with woodchips, and is something that has been proven to catch fertiliser before it gets into waterways.
Naturally occurring bacteria in the woodchips break down fertiliser chemicals and convert them into di-nitrogen gas, which is harmless and makes up most of the Earth’s atmosphere.
The bioreactor trials are part of a broader research project being conducted by Coffs Harbour City Council, Southern Cross University and Local Land Services to better manage fertiliser pollution in waterways.
Promising results, but no ‘silver bullet’
Local Land Services officer Shaun Morris worked with participating farmers to develop two different bioreactors.
The system installed at a blueberry farm in Sandy Beach was similar to those trialled in Queensland, both of which were designed to catch surface run-off.
Overall, the prototype was able to reduce nitrogen run-off into waterways by about 30 per cent. When operating at full capacity, pollution was reduced by between 73 and 85 per cent.
For Nicole Strehling, the manager of the Solitary Islands Marine Park, the results are promising.
Another bioreactor was constructed to catch the fertiliser-rich run-off coming directly from cucumber plants in hothouses.
The excess was captured and filtered through a network of pipes filled with woodchips to best filter out the nitrogens and stop the production of nitrous oxide gas, which has nearly 300 times the global warming potential of carbon dioxide.
While nitrogen run-off was reduced by 15 per cent, Mr White said it was significant considering his research showed local waterways near cucumber hothouses showed nitrogen levels 28,000 times above the ANZECC guidelines.
Modifications have since been undertaken on that bioreactor that are hoped to increase its effectiveness.
Cucumber and raspberry farmer Palwinder Singh hoped the trial on his property would demonstrate the industry was embracing sustainable practices but, he said, more needed to be done.
Mr Morris said work was being done to enhance fertiliser application practices.
“We always try and talk about the fact that [bioreactors are] not a silver bullet,” Mr Morris said.
In future, Mr White said, it was hoped the lessons from these trials would help enable further studies into bioreactors, which could play a big role in protecting waterways and marine parks.
“And then we can really protect our waterways and stop greenhouse gas emissions.”
Keeping costs down
Mr Morris said minimising the costs of a bioreactor was a big priority and would encourage farmers to install them in future.
“We’ve tried to use materials in our bioreactors that are economic and accessible to keep that cost down and make these structures far easier to build,” he said.
The structure at Bucca cost about $25,000, which is cheap compared to alternative nutrient management systems such as commercial septic systems, which cost roughly $100,000.
Back in the Solitary Islands Marine Park, Ms Strehling said the trials were a positive step toward a better balance between farming and protecting marine life.
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