When Pradhanang found a mixture of waste that could be transformed into a platform and that did not disintegrate over time, he began talking to his colleagues in Nepal. By 2021, they had secured $78,000 in funding from the Asia-Pacific Network for Global Change Research, a research and policy funder, to conduct a study in Nepal, India and Bangladesh.
While Nagdaha and the sites in India and Bangladesh do not provide drinking water to residents, they do have cultural and religious significance. On his many visits to Nepal, Pradhanang has seen children swimming in Nagdaha’s murky waters, dogs splashing on the shore, and women sitting on the banks washing dishes and clothes. Pradhanang and The Small Earth Nepal wanted to beautify the lake while cleaning it. They chose flowering plants that served both purposes: Indian watercress (Canna indica) and scarlet sage (Salvia splendens), whose bright red flowers stand out against the grey water.
After installing the floating platforms in the fall of 2022, researchers tested the water monthly and found results consistent with their laboratory testswhich showed a 99 percent reduction in nitrate levels, 80 percent in phosphates, 56 percent in iron and 55 percent in ammonia. Dissolved oxygen concentrations increased by half. Their results have been presented to the Committee Journal of Civil Engineering for review.
Growing flowering plants can add aesthetic value to a body of water, but the collaboration refrains from growing food on the platforms, as the plants generate very high concentrations of pollutants. But people aren’t the only ones intrigued by floating wetlands; geese and ducks flock to the mats, sit on the platforms and defecate phosphorus-rich droppings into the water.
Pradhanang came up with a clever solution for the naughty wild ducks: he tied silver ribbons around the stems of the plants, whose intense glow scared the birds away. Although scientists don’t want geese at the FTWS, pollinators such as bees and small birds are more than welcome, as are the various forms of microbial life that exist in the roots of plants and digest water pollutants for energy.
“There’s a phenomenon associated with floating wetlands: If you build it, they will come,” says Max Rome, who did his PhD on floating wetlands in Boston’s Charles River and now works at the Charles River Watershed Association. “These systems are really effective at creating wetland biodiversity in a place where there just isn’t room for it.”
While litter-based systems solve some water pollution problems, they leave others unsolved, such as microplastics. Incorporating local litter into the mats shouldn’t make things worse overall (much of the litter is collected from the water in the first place), but the high plastic content in the water means it may still be a health risk for locals, even after cleaning.
While Pradhanang and other outside researchers have raised concerns about incorporating polystyrene and other plastics into waste-based FTWS, they say the benefits of the mats generally outweigh the costs. “If you can use a waste product that would normally be in the water,” White says, “and you can use it to make a product that actually helps clean the water, that’s amazing.”
