Floating wetlands significantly reduce wastewater greenhouse gas emissions, study finds

A floating platform packed with native reeds and sedges has delivered a striking result in the fight to decarbonize wastewater treatment: greenhouse gas emissions from a working wastewater lagoon fell by more than a quarter during a two-year field trial in southeastern Australia. Researchers say the experiment provides the first full-scale evidence that constructed floating wetlands can reduce emissions without major infrastructure upgrades or energy-intensive technology.

The trial was conducted at a Westernport Water wastewater treatment plant on Phillip Island by scientists from RMIT University, Westernport Water and Australia’s national science agency, CSIRO. The team installed a 330-square-metre floating wetland—roughly the size of one and a half tennis courts—in one wastewater holding lagoon and compared its performance with a similar control lagoon that had no floating platform. Both lagoons continued operating under normal plant conditions, allowing the researchers to observe how the wetland performed in a real treatment environment rather than in a laboratory tank.

Wastewater treatment is an overlooked source of climate pollution. Globally, the sector is estimated to account for about 1.6% of human-induced greenhouse gas emissions. High concentrations of organic matter and nutrients such as nitrogen and phosphorus create ideal conditions for microbial communities. Some of these microbes generate methane, while others produce nitrous oxide and other gases during the biological processes used to break down pollutants. Because wastewater facilities must treat these nutrient-rich flows continuously, even relatively small changes in emissions intensity can have a substantial effect at national and global scales.

The floating wetland changed the biological environment at the surface of the lagoon. Its plants were rooted in a buoyant platform, while their root systems extended directly into the wastewater below. These submerged roots provided a vast, oxygen-variable habitat for bacteria and other microorganisms. Such microbial communities can consume dissolved nutrients and organic compounds, transforming them into less harmful forms or incorporating them into plant growth. The roots also create microscale zones where oxygen-rich and oxygen-poor reactions occur side by side, potentially shifting the balance away from microbes that generate greenhouse gases and toward those that consume or avoid producing them.

The measured reductions were substantial. Compared with the untreated control lagoon, the lagoon fitted with the floating wetland recorded carbon dioxide emissions reductions of up to 36% and methane reductions of up to 66%. Nitrogen emissions fell by as much as 18%. When the results were considered across the lagoon’s emissions profile, the researchers reported an overall greenhouse gas reduction of more than 25%. The improvements did not appear immediately: the strongest changes became evident after approximately four months, suggesting that the plant roots and their associated microbial communities needed time to establish and mature.

To track those changes, the researchers continuously monitored emissions from both lagoons over the full two-year study. They used “Pondi,” a solar-powered environmental sensor developed by RMIT and collaborating institutions, including Leading Edge Engineering Solutions, Deakin University and The University of Queensland. Continuous monitoring is important because gas emissions from wastewater ponds can vary with temperature, sunlight, rainfall, wind, organic loading and seasonal biological activity. Rather than relying on occasional samples, the sensor system allowed the team to observe emission patterns over extended periods and compare the floating-wetland lagoon with the control under changing operational conditions.

Study first author Dr Lukas Schuster of RMIT University said the results demonstrate that floating wetlands can do more than remove nutrients from wastewater. “This is the first time we’ve had evidence on this scale that supporting microbial communities in the root systems of wetland plants can reduce wastewater emissions without relying on high-tech solutions,” Schuster said. He described the findings as a strong example of how nature-based systems could turn wastewater treatment into part of the climate solution. The plants do not replace the treatment process, but add a biological layer that can influence the chemistry and microbiology of the lagoon.

The approach also offers a practical advantage for water utilities: the platforms can be retrofitted into existing lagoons. That means operators may be able to reduce emissions without rebuilding ponds, installing complex gas-treatment equipment or significantly changing established treatment processes. Westernport Water Managing Director Dona Tantirimudalige said the findings provide a foundation for testing the technology across different lagoon designs and operating conditions. She noted that utilities need credible and cost-effective ways to meet emissions targets while maintaining reliable wastewater services, particularly in regional areas where capital and energy resources can be limited.

CSIRO is now developing and applying floating wetlands through its nature-based solutions program. In addition to reducing greenhouse gas emissions, the systems may capture or transform contaminants before treated water is released into downstream ecosystems. Their ecological value could extend beyond water quality: floating vegetation can provide habitat for microorganisms, invertebrates and some wildlife, although the trial required ongoing maintenance, including weed control and measures to deter birds from damaging the plants. The researchers emphasize that performance will depend on factors such as plant selection, platform coverage, lagoon design, wastewater composition and local climate.

The Phillip Island project is already inspiring a broader experiment. RMIT researchers, working with Melbourne Water and the Bass Coast Landcare Network, are testing floating wetlands in farm dams across the Bass Coast region. That work is examining water quality, biodiversity and emissions reductions, with the possibility of applying the technology to some of Australia’s approximately 1.8 million farm dams. If the systems perform reliably in agricultural environments, they could become a flexible tool for managing nutrient pollution and supporting biodiversity across landscapes far beyond wastewater plants. The wastewater study, titled “Constructed floating wetlands cut greenhouse gas emissions from wastewater lagoons,” appears in the Journal of Environmental Management and marks a significant step toward making engineered wetlands a measurable component of climate mitigation.

News Publication Date: 15-Aug-2026

Web References: https://bg.copernicus.org/articles/22/5051/2025/; https://www.csiro.au/en/research/natural-environment/water/constructed-floating-wetlands; https://www.rmit.edu.au/news/all-news/2026/apr/floating-wetlands-bass-coast; https://www.rmit.edu.au/research/centres-collaborations/centre-for-nature-positive-solutions

References: Journal of Environmental Management. DOI: 10.1016/j.jenvman.2026.130663