Floating wetlands for nutrient removal in eutrophicated coastal lagoons: Decision support for site selection and permit process

Lagoons often suffer from eutrophication. Floating islands planted with native emergent macrophytes offer a solution for internal nutrient removal. These'active barriers' have been applied in various inland waters, but never in coastal and marine environments. First coastal floating wetlands were installed in different lagoons along the Southern Baltic Sea. However, prior to these installations a comprehensive site selection and permit process had to be carried out. Participatory mapping was performed, law regulations in five European countries investigated and open-source data was integrated to evaluate where suitable installation sites would be. Regional environmental conditions influence how a floating wetland is designed, planted and installed, but do not limit the choice of installation sites explicitly. Restrictions and site choices depend largely on 'social preferences' and legal requirements. The participatory mapping showed that visibility of the floating wetlands is important. The proximity to the shore, and hence to potential bathing sites, as well as the proximity to larger cities or tourist destinations are important decision-making factors. The legal steps in the permit process differ in European countries and transferability is difficult. However, all case studies share in common that open waterways and undisturbed maritime traffic are a priority. All investigated lagoons belong to the European Natura 2000 network and are protected habitats. Nevertheless, this does not per se have to complicate the permit process for floating wetlands as the aim of the macrophyte islands is in accordance with the regional, national and European laws on nature protection. A variety of scientific articles proved the usefulness of floating wetlands for nutrient removal in mesocosm experiments. It is time to pave the way for pilot installations in coastal waters. This study with its overview tables on European regulations and graphical visualization serves as a guideline and decision support tool for site selection and permit process.