Constructed floating wetlands made of natural materials as habitats in eutrophicated coastal lagoons in the Southern Baltic Sea

Abstract

Eutrophication remains an environmental challenge in lagoons along the Southern Baltic Sea. Floating islands planted with emergent macrophytes are an option to remove nutrients from eutrophicated waters. Furthermore, floating wetlands offer other ecosystem services such as the provision of habitats. Numerous scientific studies have been conducted; however most remain on the laboratory scale. This research explores the challenges associated with installations in coastal environments and focuses on sustainability of the island design, the habitat function as well as nutrient removal. Most floating wetland designs use polyethylene, polypropylene, polyurethane or polyvinyl alcohol foam to ensure the buoyancy. For this study an artificial polymer free island design was developed and tested. The floating constructions in the Darss-Zingst-Bodden-Chain were planted with native macrophytes which have the potential to act as ‘biodiversity-supplements’ to the adjacent coastal wetlands: Bolboschoenus maritimus, Carex acutiformis, Iris pseudacorus, Juncus effesus, Lythrum salicaria, Schoenoplectus lacustris, Typha latifolia. The chosen macrophytes survived fluctuating salinities. After three months the above-ground biomass was harvested and analyzed for the nutrient concentrations. Phosphorus concentrations were highest in L. salicaria and nitrogen in I. pseudacorus. Video monitoring and field observations were applied in order to observe animals. Birds did not use the floating wetlands as breeding grounds, but the grey heron (Ardea cinerea) was a common visitor for foraging. Especially surprising was the large amount of juvenile eels (Anguilla anguilla). A diverse and large root network below the floating islands boosts not only nutrient removal but serves as a shelter and refuge for fish such as the endangered eel.

Screening Life Cycle Environmental Impacts and Assessing Economic Performance of Floating Wetlands for Marine Water Pollution Control

“…Thus, it is of primary importance to study the FWs system in simulated coastal conditions to assess its durability and lifespan. This research challenge was also identified in the bibliometric analysis of Colares et al [37], and the research work of Karstens et al [38] who indicate that most studies about FWs remain on the laboratory-or pilot-scale, and point out the need to assess the behavior of the floating carrier in the natural environment.…”

Ecosystem Service Assessments within the EU Water Framework Directive: Marine Mussel Cultivation as a Controversial Measure

“…The applied ecosystem service assessment is based on the Marine Ecosystem Services Assessment Tool (MESAT) [32]. In general, MESAT assesses changes in ES provision between different time periods [32], but it can also be used for different scenarios [33]. It is based on the Common International Classification of Ecosystem Service (CICES) and can be applied in a qualitative and semi-quantitative way.…”

“…In addition, floating islands attenuate wave energy and water flow and are consequently able to enhance particle settling and nutrient burial [38][39][40]. Floating wetlands with native emergent macrophytes were tested for the first time in Baltic lagoons in 2018 [39,40] and turned out to be a valuable refuge for aquatic fauna such as the endangered eel [33].…”

“…It should be noted that only the selection "no measures" was made at the German workshop in Stralsund. Geoengineering measures (GE) Red 0 0 5 (33) [100] 5 {9} Comparisons between the different nationalities of the participants were difficult to conduct, as the workshops in PM2 and PM3 were conducted on an international level (Table 1), and the participants involved were of different nationalities. However, a comparison could be made between the different results from PM1 and PM3, as local stakeholders (non-scientists: Germany = 69%; Lithuania = 50%) participated in both workshops.…”

From water quality to river health

“…For many urban water bodies native vegetation, both riparian and submerged, are scarce to non-existent compared to less altered aquatic ecosystems. In these cases FTW vegetation may mimic natural wetlands and play multiple roles (O'Hare et al, 2018), providing a refuge for small fish and a forage ground for birds (Karstens et al, 2021), a food source for larval insect (e.g. lepidoptera) (Gross et al, 2001), and a complex physical environment on both the micro and macro-scale (Dibble et al, 2006).…”