Floating treatment wetlands as multi-functional ecosystems – from anecdote to evidence

Blog post by Jonathan Fletcher

Floating treatment wetlands (FTWs) are buoyant frames supporting emergent aquatic plants which allow the expansion of planted vegetation across the water surface. These novel freshwater restoration systems are most commonly employed as tools to improve water quality in small water bodies. Additional ecosystem service provision, such as increased habitat, is often alluded to in published research, or by practitioners, although there has been no known attempt to quantify the multiple ecosystem services that these systems provide. Understanding how FTWs operate as distinct ecosystems and interact with the wider living and non-living environment will lead to an appreciation of their full value as freshwater restoration tools. Airthrey Loch is a water body with multiple pressures including nutrient enrichment, invasive species and periodical algal blooms making it an ideal location to undertake a field trial investigating this freshwater restoration technique.

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Floating treatment wetland experiment set-up with enclosures on Airthrey Loch

Specific ecosystem services have been selected based on their management relevance and freshwater restoration potential including:

  • Habitat provision for fish and freshwater macroinvertebrates and the influence on abundance and diversity of these communities
  • Sedimentation i.e. the degree to which FTWs can increase the amount of bed sediment and quality
  • Aesthetic/cultural value from loch users
  • Water quality improvements
  • Resource recovery from harvesting plants

An important decision that environmental managers would make when employing FTWs is which plant species, or combination of plants to use. Here we distinguish between two different native plant communities; a monoculture of Phragmites australis (Common Reed), and a diverse community including Alisma plantago-aquatica (Water Plantain), Juncus effusus (Soft Rush), Lythrum salicaria (Purple Loosestrife) and Myosotis scorpioides (Water Forget-Me-Not). Both plant communities will result in different above and below ground plant morphology and structure; key characteristics that may influence the chosen response variables. By accounting for these differences between plant communities, the balance of ecosystem services generated by plant selection can be understood allowing environmental managers to target their preferred functions.

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Assembling the FTWs and planting with the experimental plant communities

This study will run on the University of Stirling campus from May 2019 to September 2020 with sampling carried out throughout the year to capture seasonal variability. This study is part of a wider Ph.D. project being carried out by Jonathan Fletcher (Biological & Environment Science) along with his supervisor team of Professor Richard Quilliam, Professor Nigel Willby and Dr. David Oliver.

Acknowledgements

Funding provided by The Scottish Government’s Hydro Nation Scholar Programme.

Thank you to the following for their support: Alan Law, Alexandre Davis, Colin Bull, Hannah Dry, Gardens and Ground Staff, H&S team, Isobel Swinscoe, Jim Blaikie, H&S team, Natalie Boyd-Williams, Sarah Buckerfield, Sophia Riederer, University of Stirling Angling Club.