Floating wetland cuts wastewater lagoon emissions by up to 31%

A floating wetland installed in an Australian wastewater lagoon cut combined greenhouse gas emissions by 22% to 31% in a two-year trial, offering early evidence that plants on buoyant platforms could help reduce the climate impact of water treatment.

Researchers placed a roughly 330-square-metre platform planted with native reeds, rushes and sedges in one channel of an operating holding lagoon on Phillip Island, Victoria. A parallel channel without a wetland served as the control, while sensors continuously monitored carbon dioxide, methane and nitrous oxide.

Compared with the control, methane emissions fell by 32% to 66%, carbon dioxide by 24% to 36%, and nitrous oxide by 18%. The reductions became apparent within four to seven months, before substantial changes in nutrient concentrations were detected. This suggests that nutrient uptake by plants does not fully explain the effect, although the precise combination of biological and physical processes remains uncertain.

Vegetation harvesting caused brief methane spikes, which subsided within a month. The researchers also caution that the experiment covered two channels at one site rather than the entire lagoon, so further trials are needed across different climates, lagoon designs and operating conditions.

Floating wetlands can be added to existing ponds without requiring more land or major infrastructure changes, making the approach a potentially practical complement to other emissions-reduction measures.