Floating Wetlands in the Puget Lowlands: Design, Construction, and Viability

Thesis (Master's)--University of Washington, 2016-06

Floating wetlands are rafts that host wetland plants, supporting wildlife habitat and contributing to improved water quality. Floating wetlands have been developed and deployed worldwide to restore wetland structure and function to degraded urban aquatic environments. Informed by river and wetland structure and function, as well as by "naturally occurring" floating wetlands, this research involved developing, building, monitoring and assessing one dozen new floating wetland designs intended to improve plant and animal biodiversity in degraded urban aquatic environments of the United States Pacific Northwest. From 2013 to 2016, field research was conducted on plant species’ overwintering, volunteerism, and position relative to water surface within these rafts. The most successful planted species was Juncus ensifolius (dagger-leaf rush), showing a 100% survival rate and volunteering in 20% of rafts. The most prolific volunteer was Epilobium palustre (marsh willowherb), present in 65% of rafts. This thesis provides a preliminary understanding of how the various raft designs and plants fared, and offers insights for improving upon the designs. Knowledge gained from the research will inform plant selection as well as future studies evaluating usage of floating wetlands by fish and wildlife in the region.