Mossy cane drains improving water quality

Mossman farmers are adding vegetated drains to their toolbox of practices that are improving the quality of water leaving farms. Seven new farm drainage improvement projects are being implemented in the region and will treat almost 200 hectares of cane farming land.

Mossman Ag’s Rebecca McHardie explains that vegetated drains are shallow channels that have primarily been designed to move water off a farm, and are then retrofitted to enable nitrate removal.

“With slight modifications to their drains, farmers are essentially getting them to also function as a man-made wetland. As happens in natural wetlands, nitrate is removed from the water through a microbial process and released back into the atmosphere as harmless nitrogen gas.”

To effectively remove nitrate, drains need to be shallow, have water in them for most of the year, and have the right density of vegetation in the drain. Modifications for each site varied depending on the landscape characteristics, but generally involved earthworks to reshape and reprofile, and then planting native grass species.

Rebecca said that one project is also planning to vegetate the edges of the drain to transition it into a riparian zone.

“Drains and creeks with vegetated banks have additional benefits for water quality. It acts like a buffer strip that reduces soil loss or erosion.”

The use of vegetated drains as a farm treatment system is relatively new. The concept was first trialled as part of a reef water quality project in the Tully and Johnstone regions which ended in 2021. The project was able to demonstrate the effectiveness of, and quantify the amount of nitrate removed from, vegetated farm drains when they met the right criteria.

The drainage improvement projects in Mossman were made possible through a Prod180 small grants round that was designed by Mossman Ag with input from local growers.