March 28, 2024

Floating wetlands strengthen urban ecosystems and community engagement

In 2018, Friends of Green Lake initiated the floating wetlands project to commemorate the life of Taiga Hinckley, a beloved employee of the Greenlake Boathouse Center. The project was selected to reflect Taiga’s commitment to lake water quality and wildlife habitat. Herrera contributed to the project design, planning, and installation, and worked with over 30 volunteers to execute this project.

The floating wetlands consist of two 650-square-foot islands anchored in the lake. In such an urban setting, the floating wetlands create habitat, improve water quality, provide aesthetic and recreational value, and foster opportunities for community engagement.

Floating wetlands are artificial floating structures designed and installed to mimic natural wetland ecosystems in bodies of water. These structures typically consist of a buoyant platform that supports vegetation and other wetland flora. The purpose of floating wetlands is to provide ecological benefits, such as habitat creation and water purification, while also addressing human activities that may negatively impact natural wetland areas.

Photo by Rob Zisette [enlarge]

One of two mature 650-square-foot floating wetlands in Hicklin Lake in White Center, photographed ten years after Herrera installed them for King County.

Floating wetlands provide an innovative approach to environmental challenges, and can be designed to address a range of problems. They play a role in water quality improvement by fostering the growth of a microbial biofilm on the roots of plants. This biofilm actively absorbs excess nutrients from the water, reducing issues like harmful algal blooms and promoting a healthier aquatic ecosystem. Additionally, the shading effect created by floating wetlands can help regulate water temperatures, particularly in stormwater ponds, contributing to improved downstream fish habitats.

Herrera recently designed and helped install floating wetlands in a stormwater pond for the Snoqualmie Tribe. The aim of this project was to improve water quality and reduce pond temperature. Herrera Ecologist Eliza Spear explains the benefit of using floating wetlands to reduce water temperatures, “By covering a significant portion of the surface area of the stormwater pond, the goal was that the floating wetlands would provide enough shade to cool water temperatures, which is important for enhancing downstream fish habitat. Fish are very temperature sensitive, so reducing water temperatures can improve fish habitat in the basin.”

Beyond their water quality contributions, floating wetlands serve as habitats, supporting a diverse mix of plant species and wildlife. The modular design of these structures allows for flexible and creative habitat configurations, addressing specific environmental goals and conditions. This biodiverse ecosystem enhances the overall health of the water body and provides opportunities for community engagement. The presence of floating wetlands in urban environments sparks curiosity and fosters a sense of ownership among communities. Volunteers participate in installation and maintenance activities, contributing to both the success of the project and the environmental education of the community.

Floating wetlands offer an aesthetic and recreational dimension to water bodies. Their integration into urban landscapes provides unique opportunities for public interaction, such as viewing the structures from shore or anchoring them to piers or bulkheads with direct access to them. The ease of installation and adaptability of floating wetlands make them a cost-effective and resilient choice for environmental enhancement, providing an attractive alternative to traditional land-based restoration projects. At about $50 per square foot, they can cost less than 10 percent of a constructed wetland because there are no land procurement or excavation costs, permitting is simpler, and plant survival is much higher on the water. Overall, these innovative structures not only address urban environmental challenges but also contribute to the creation of sustainable, community-centered ecosystems with long-lasting benefits.

Photo by Eiza Spear [enlarge]

Green Lake Taiga Floating wetlands after installation.

Rob Zisette, a Principle Aquatic Scientist at Herrera, has championed floating wetland projects since 2008. Rob has had a diverse career working in water quality and aquatic restoration and floating wetlands became his focus after he was introduced to them while working on a water quality project in Ningbo, China. Rob met the owner and inventor of Biomatrix Water, Galen Fulford, who creates highly resilient structures for floating wetland projects. After seeing the power and potential of floating wetlands, Rob has spent the last 15 years bringing them to the Pacific Northwest.

However, floating wetlands are not without controversy. In Washington State, many regulatory agencies view floating wetlands similar to docks and require mitigation for their installation- ironically, while others view floating wetlands as a type of mitigation. Some believe floating wetlands threaten salmon because predator species can hide under the structure, while research by the University of Washington has shown that not to be the case. Agencies in other states but not Washington provide mitigation credits for installing floating wetlands in stormwater ponds.

The value of floating wetlands is challenging to quantify. Significant water quality improvement is often not observed because pollutant concentrations are so highly variable and too small of the waterbody area is covered to produce measurable change. Habitat and ecological value are rarely measured and typically undervalued or not recognized. Qualitative observations have shown that these floating ecosystems provide essential habitats for juvenile fish feeding on the biofilm invertebrate community and for bird species browsing and nesting on the wetlands, which contribute to biodiversity and overall ecosystem health and value. Moreover, the vastly improved aesthetics, environmental education opportunities, and shared sense of ownership they create bring intangible value to urban water visitors and surrounding residents.

Rob’s vision for floating wetlands in the next 10 years includes a gradual increase in projects in the Pacific Northwest, increased visibility through high-profile initiatives, and a focus on retrofitting stormwater ponds where benefits are most pronounced. In addition, the development and acceptance of crediting systems for floating wetlands is crucial to fund these projects, and will require further education of the public and regulatory agencies about their many benefits.

Lily Schreder is a marketing specialist at Herrera with a background in marketing and environmental studies.

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