Reservoir Blogs …No.3

Armed with 500 plug plants and a small inflatable boat, aquatic specialists from Frog Environmental recently made a return visit to the reservoir in Yarner Wood to assess the success of the restoration works started in December 2018. It’s not often you see a small boat on the reservoir, but working on the water is all in a day’s work for this specialist team, and simply the best method for making checks on the newly installed floating islands. These vegetated rafts were just one of the ingenious techniques used to make the reservoir more inviting for wildlife. Since the start of the project, this concrete edged reservoir has been transformed by replicating natural processes such as felling trees around the water’s edge. This man-made structure is starting to return to the wild, but there are always improvements to be made and so six months on, it was time to get out on the water and take a closer look.

Frog Environmental supplied additional plants for the floating rafts, including yellow flag iris, meadowsweet, marsh marigold and cotton grass

Once on the water, one of the key tasks was to make some checks and improvements to the vegetated rafts. These innovative structures are deliberately placed to imitate the ‘randomness’ of natural islands, constructed from an aluminium frame, the rafts vary in size and are designed to sit at different heights above the water to favour different plant species – they are then connected to form larger floating islands. Frog Environmental were able to check the anchor points of the rafts and with trays full of new plug plants they supplemented the original planting, with species such as yellow flag iris, meadowsweet, marsh marigold and cotton grass. A wide variety of plant species have been planted to provide structural diversity to the islands; low growing and taller species will provide a refuge for nesting water birds and improve the site for invertebrates.

A heron standing on one of the floating islands (Photo: Phil Page)

On closer inspection, the team found the roots of some of the plants already extended one foot below the rafts even though there were only put in the reservoir in March this year. These roots extending into the water will help to improve the water quality of the reservoir and as part of the longer term monitoring, water samples will be taken every three months to monitor change. They also provide a vital refuge for young fish, invertebrates and zooplankton.

Marsh cinquefoil (NE/Neil Pike)

In addition to the additional planting on the surface of the rafts, project manager Fergus Mitchell (Natural England), wanted to add an extra element to the islands. Armed with a bucket and spade, he made a visit to Goss Moor National Nature Reserve – this watery site has a similar mix of acid heathland and soil chemistry to East Dartmoor and he saw the perfect opportunity to transplant a small selection of floating plants, such as marsh cinquefoil (cinquefoil meaning five leaves). Back at East Dartmoor, these new plants were anchored to the edge of the floating islands; Fergus hopes they will grow to form vegetation rafts that extend out from the engineered rafts and provide much needed cover and protection for the aquatic fauna.

Installing the new kingfisher nesting burrows. Bottom photo: The artificial burrows were covered with earth and planted

There has been a final interesting addition to the restoration work at the reservoir. Kingfishers have regularly been spotted around the reservoir, but the reservoir’s solid concrete edges do not provide any opportunity for kingfishers to excavate their nesting burrows. Never to be daunted by a challenge, Bryan Thorne and the Natural England ‘Tuesday Group’ volunteers took on the task – three artificial burrows were purchased and a suitable site was identified perched above the water’s edge. The volunteer team were able to extend the old Victorian reservoir wall to site the three new burrows; these large structures are designed to replicate a natural kingfisher burrow with a tunnel leading to a nesting chamber. They added sand to the entrance ways as kingfishers like the illusion of excavating the holes. The volunteers will be carefully observing activity around these burrows next spring!

New flowering plants around the margins

The vision for this restoration project was to replicate natural processes and structure, by felling trees into the water for example, the project team have cleverly borrowed ideas from nature and artificially created natural features, such as islands, marginal vegetated areas and surface cover using floating-leaved plant species. In combination, these measures will add complexity to the reservoir site and lay the building blocks towards creating a diverse and thriving habitat for aquatic wildlife.

This has been a unique project for the team here at the National Nature Reserve and you can read the complete story of this restoration project in our series of Reservoir Blogs, describing the project from start to finish – No.1 Work to the Reservoir Starts! and No.2 Transforming the Reservoir – Work Completed!

Panoramic view of the reservoir 2019

This project was funded by the National Lottery Heritage Fund as part of the Moor than meets the eye Landscape Partnership scheme on Dartmoor, which after 5 years of work across Dartmoor, is drawing to a close at the end of this year.

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