Vegetated Drains: Making Mini Wetlands
With thousands of kilometres of farm drains criss-crossing the Wet Tropics, what if they could be turned into mini wetlands to improve water flowing to the Great Barrier Reef?
Farms drains are being turned into mini wetlands and trialled as a system for removing nitrate from farm runoff
Farm drains are getting a makeover. They’re becoming the new ‘no-frill’ wetlands of the Wet Tropics as farmers and scientists combine to find effective ways to reduce fertiliser and pesticide runoff.
Jack Murday is one of seven cane farmers in the Mossman district who are modifying drains to help slow down water flows, reduce erosion and remove nitrates from the water.
He and his father have planted native grasses and sedges in a drain after making it wider and shallower and building rocky retaining dams to slow down the flow of water. Now that it’s more like a natural wetland, plants can take up the nitrogen and microbes can convert it into harmless nitrogen gas that’s released into the atmosphere.
The Murday family’s vegetated drain is treating nine hectares of cane paddock – and contributing to 200 hectares of cane farming land that’s being serviced by vegetated drains in the Mossman area through a reef water quality project delivered by Mossman Agricultural Services and Terrain NRM.
“Before we retrofitted the drain, it was narrow, steep and eroding,’’ Jack says. “The only way to maintain it was to spray the weeds out. The drain’s new shape means we can slash rather than use spray, preserving the nitrate and sediment-capturing vegetation.
“Having the right density of vegetation in the drain means we can trap sediment and treat nitrate in the water. It aligns with our farm’s long-term management plan to reduce our inputs and improve production, sustainably.”
The ecological benefits of restoring wetlands are well-known, but the characteristics that vegetated drains share with wetlands mean they can act as a cost-effective system for treating nitrate.
Further south, a series of trials in the Tully and Johnstone catchments as part of the Wet Tropics Major Integrated Project have proven that vegetated drains, in the right conditions, have good potential as water quality treatment systems. In the neighbouring Murray catchment, farmers, scientists, wetland experts and environmentalists have met to share lessons learnt so far and talk about drain shapes and plant species for different locations and purposes.
The next step is developing guidelines for farmers.
This Murray region workshop was delivered by Terrain NRM, Sugar Research Australia and the Department of Agriculture and Fisheries (DAF). It was funded through the Australian Government’s Reef Trust in partnership with DAF, through the Queensland Government’s Queensland Reef Water Quality Program.
Ideal conditions for nitrogen removal
- A good amount of organic matter in the soil
- Permanent water – not too deep
- Constant water flow – not too fast or slow
- Neutral water – a pH of 5-7
- Good plant cover – not too much or too little