Following 15 bioreactor trials, the Queensland Government (DAF) has released new guidelines that collate and synthesize the data about using denitrifying bioreactors to improve water quality runoff from farms.
Bioreactors are woodchip filled trenches that intercept and treat nitrate in surface run-off or shallow ground water on farms. The guidelines will help land managers and farmers decide whether a bioreactor will be effective on a particular site and if so, how to design, construct and maintain it to maximise the removal of nitrate.
The bioreactor guidelines are based on four years of research from projects including the Wet Tropics Major Integrated Project (MIP), which has been trialling a number of catchment repair treatment systems, together with literature published overseas.
Wetlands expert Carla Wegscheidl said lots of lessons had been learned along the way with some bioreactors being flooded and others trampled by feral pigs. The presence of algae and sediment also cause challenges.
“Bioreactors are relatively simple, passive treatment systems that can be installed in farm-drains, or headlands without impacting farm operations,” she said.
“The carbon in the woodchip, and low oxygen environment, provides the right conditions for microbes to convert nitrate in the water into harmless nitrogen gas through the process of denitrification. This process naturally occurs in wetlands and waterlogged soils. Microbes are already present in the soils.”
MIP Catchment Repair Coordinator Chris Algar said the input from participating landholders has been a crucial part of the process.
“With the help of landholders we've been able to trial a range of different bioreactor designs in the Major Integrated Project, each designed to suit the landscape they’re positioned in. There’s no one size fits all solution - variability of soil, land and water flow all mean we need to tailor each bioreactor to the conditions,” Mr Algar said.
One advantage of bioreactors is the minimal impact they have on productive land.
“Only a small amount of land is required for a bioreactor and it doesn’t need to be positioned on existing farmland. The ideal conditions for a bioreactor site is an area that’s freely draining where leaching is occurring in the soil,” said Mr Algar.
Ms Wegscheidl said the trials couldn’t have been completed without the help of the Bioreactor Network, whose members include Jaragun EcoServices, Terrain NRM (Wet Tropics Major Integrated Project), James Cook University, Queensland University of Technology, Australian Wetlands Consulting and the Department of Environment and Science.
“It was truly a collaborative effort,” she said.
The guidelines were developed as part of the Bioreactors for Great Barrier Reef and the Agricultural Water Treatment projects, with funding from the Queensland Reef Water Quality Program.