Putting right man’s mistakes to help improve biodiversity

A digger works on improving the canalised part of the river
A digger works on improving the canalised part of the river

Most people would not expect to see a conservation body using a digger to push soil into a river.

But that is what the British Trust for Ornithology started doing last week as part of £???? worth of improvements to its only nature reserve near its Thetford headquarters.

A new earth bank protects the left bank of the meanders

A new earth bank protects the left bank of the meanders

Its head of projects Nigel Clark said: “Unfortunately, you can’t leave these things to change naturally because we’ve altered the rivers so they don’t behave naturally.”

It is man’s interference with the River Little Ouse running through the reserve, which the trust has owned since it moved to Thetford in 1991, that has reduced the wildlife value of this section and its river valley.

To aid gravel extraction from what is now Nunnery Lakes, the river was canalised in the 1970s as a steep sided, straight channel, taking the water away from its natural meandering course through the reserve’s water meadows.

In 1994, the meanders, which remained in the uncultivated meadows, were reinstated.

Chris Gregory, left, and Nigel Clark

Chris Gregory, left, and Nigel Clark

Standing beside the meanders, Nigel explained: “This was flooding and remaining flooded the whole time. The river was also scouring it out. What’s important for the birds is the muddy edges.”

The area is also low in invertebrates, on which the birds feed, because when it floods they are washed away.

Last week the diggers created a bank alongside the meanders, which will allow the trust to manage the water levels, so the meadows can flood in winter and be allowed to drain for the summer for breeding birds.

Nigel said: “In winter a lot of migrating birds pass through the area and need places to stop and refuel.

“This will also be really good for some of the local breeding species, like lapwings. They do breed here but not in large numbers.”

The site’s whole biodiversity will benefit not just the birds. Reserve manager Chris Gregory said: “That’s what this funding is all about, biodiversity. We’ve got target species, but it will benefit many more.”

But Nigel said: “If you ask for money to protect, say, reed warblers and reed beds you stand a chance of getting it.

“ If you ask for money for some small insect that’s critical for the reed warblers, you’ll struggle.”

It could help people, too. Nigel added: “This will still act as flood relief. This area takes in water and slowly lets it out.”

Across the reserve, Chris points out the straight channel poor flow and environmental consultant Nigel Holmes explains: “Effectively, you’ve got a dead river. It’s just here as an overflow of flood water when required.”

He says that has left it with poor flow at other times and a deep muddy bottom, too unstable for things to grow. In summer the water is very low in oxygen, leading to algae blooms and even botulism.

So a digger was putting soil back into the channel to create a variety of depths and encourage plant growth, as well as lowering the banks. The hope is to put life back into it.

But improvements to the reserve will not end when the diggers leave. Nigel Clark says they have a lot of scrub removal to do, to stop it becoming mature woodland, which is a less important habitat here.

They also plan to do research on the best way to manage marginal reed beds on the lake, which will benefit other reserves.

The total cost of the project is £211,383 of which £197,583 comes from Waste Recyling Environmental (WREN).

WREN uses Landfill Tax money to fund projects in communities affected by landfill. That figure incudes ‘seed’ funding from Thetford Town Council and the Nunnery Lakes Fishing Syndicate.

There was also £5,000 from the Environment Agency, a £5,000 legacy from BTO member Terry Smeeton and £3,800 match funding and volunteer in-kind.