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  • Heidi E Golden

Biofiltering Floating Islands

Updated: Feb 11, 2021

My first research position as a young, budding scientist examined the role of eutrophication, over enrichment of a water body with nutrients. Nitrogen and phosphorus are the most common nutrients leading to eutrophication and usually come from agricultural, household, and industrial run-off. Although these nutrients are essential for primary production, in excess they cause algal overgrowth and can lead to oxygen depletion, harmful algal blooms, and fish death. How can eutrophic ecosystems be restored to healthy aquatic habitats if these nutrients can not be controlled or reduced at their source? Recently, I worked with the aquatics team at Princeton Hydro (PH) on a creative solution to this eutrophication problem: Floating Wetland Islands!


Floating wetland islands are loosely analogous to huge fish tank filters, which filter small particles and facilitate denitrification, the reduction of nitrate and nitrite by microorganisms to molecular nitrogen. Floating wetland islands utilize the synergistic relationship between certain wetland plant roots and their associated microorganisms to help improve water clarity and reduce harmful nutrients in eutrophic aquatic ecosystems. The floating islands are made from fibrous material and provide a platform for plants, enabling their roots to dangle below the water's surface and to create an ideal microbial habitat. Plant roots provide substrate and food for beneficial microorganisms, while microorganisms produce a food source for the plants and remove excess nutrients from the water. Katie Walston led our team of volunteers and PH scientists (me and Pat Rose) in helping Camp Hope, an educational and recreational facility for underprivileged children in New Jersey, improve their water quality and aquatic habitat by planting and installing five floating wetland islands.


We used a variety of native plants, including Blueflag Iris, Shallow Sedge, Swamp Milkweed, Blue Lobelia, Swamp Rosemallow, spotted Joe-Pye, and Green Bulrush, for these floating wetland islands. They will eventually grow to provide surface area and an organic carbon source for beneficial, denitrifying microorganisms. And, they will look beautiful, too.


A mixture of peat moss and top soil gives this young milkweed plant its start. In addition to improving water quality through its roots, milkweed's above water biomass will provide food and habitat for pollinators, such as Monarch butterflies.


Maneuvering one of the floating wetland islands into place within Camp Hope's eutrophic, algae and lily choked aquatic system.


Two of five floating wetland islands installed and ready for action. Fingers crossed that these biofilters will function as planned to help improve water quality and aquatic habitat for Camp Hope.


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