Wetlands Australia 33: Wetlands are key to solving the nitrogen problem of the Great Barrier Reef

Author: Fernanda Adame Vivanco, Australian Rivers Institute

Wetlands play an important role in improving the water quality in the Great Barrier Reef.

Nitrogen pollution is one of the greatest environmental challenges of our times. In the Great Barrier Reef, excess nitrogen has caused the deterioration of water quality and the reef.

The discovery of fertilisers in the 1960s allowed the increase in food production, which has sustained continued population growth. In this century, fertiliser use has increased from 12 to 85 million tonnes annually. However, most of the fertilisers applied are not consumed by crops and end up in waterways and coastal ecosystems, causing degradation. Our research has shown that wetlands are a natural and cost-effective strategy to reduce nitrogen pollution and improve water quality in the Great Barrier Reef.

Natural wetlands surround a sugarcane plantation in the Herbert Catchment, Queensland. Photo: Fernanda Adame Vivanco.

Wetlands can remove nitrogen through a process called denitrification, in which nitrates in the water are converted to nitrogen gas. This process is done by bacteria living in waterlogged soils that feed on the nitrogen and carbon of the wetlands. Typically, runoff from agricultural land is about 25 kg of nitrogen per hectare per year;  an area of 0.05 hectares of wetlands could remove all this nitrogen through denitrification, preventing it from entering the reef.

So far, strategies to solve the nitrogen pollution problem in the Great Barrier Reef have been on-farm activities, such as reduction of fertiliser use, or technologies, such as improvements in water treatment plants. But many of these strategies are challenging to implement or prohibitable costly. Wetlands are highly efficient at removing nitrogen while providing additional co-benefits such as bird habitat, carbon sequestration and flood protection.

Finally, construction of wetlands can be very cheap, for instance, by modifying drains to create conditions that facilitate denitrification. The creation of wetlands could provide a cost-effective solution for farmers to reduce nitrogen pollution in the Great Barrier Reef and throughout Australia.

A modified drain could effectively work as a wetland and reduce nitrogen runoff from a farm. Photo: Fernanda Adame Vivanco.