How Sheffield’s moors can soak up city’s flood risk

Professor Ian Rotherham and Dr Paul Ardron at the top of the Porter catchment near Ringinglow Bog with Sheffield in the background
Professor Ian Rotherham and Dr Paul Ardron at the top of the Porter catchment near Ringinglow Bog with Sheffield in the background

Let’s imagine that Sheffield Council was the lucky owner of a giant sponge nearly two miles wide as it addresses the issue of flooding. The sponge has been badly damaged for over 100 years, but it’s still there, and actually appears to be repairing itself.

“Sphagnum is absolutely beautiful,” said Dr Paul Ardron, as he squelched through Ringinglow Bog. “And if there are a good number of species, it’s a good indicator of health.”

Dr Paul Ardron examining some blunt-leaved bogmoss

Dr Paul Ardron examining some blunt-leaved bogmoss

Why is sphagnum moss so important? Professor Ian Rotherham of Sheffield Hallam University could spend many hours telling you about its historical and ecological significance, but instead he grabbed a fist-sized handful of bog moss and squeezed out a steady stream of peaty liquid. “Sphagnum holds 20 times its own weight in water,” he said.

So, Sheffield’s Ringinglow Bog is effectively a giant sponge straddling the head of the Burbage Brook and the top of the River Porter’s catchment area on the edge of the city. There are similar sponges around the catchments of the Sheaf, Rivelin and Loxley.

During their recent research for the British Ecological Society, Paul and Ian have identified over a dozen species of sphagnum moss on the moors around Burbage and Ringinglow during identification training programmes for local, national and international moss finders.

It’s all very exciting, said Ian and Paul, as they squelched around Ringinglow looking for Bog Andromeda, not a 1960s ‘Outer Limits’ TV character, but a small shrub reappearing on Ringinglow after an absence of 30 years.

Professor Ian Rotherham showng the water held by a clumb of sphagnum moss

Professor Ian Rotherham showng the water held by a clumb of sphagnum moss

(Paul helpfully advised caution when exploring an open-access swamp with peat up to 10 metres deep in some places, and which is rumoured 30 years ago to have swallowed a full-size gas pipeline excavator.)

A healthy layer of moss protects peat from erosion and oxidisation, Ian said, and rare ‘peat forming’ moss species returning to Sheffield’s moors after years of decline are now ready to start forming new peat to lock in water and carbon dioxide for years to come. Peat itself is like a sponge, and Paul said local peat landscapes can rise and fall as they absorb water over the seasons.

One hundred years ago, Sheffielders knew all about ‘bog moss,’ as they were asked to gather sphagnum from their local bogs to provide dressings for soldiers injured fighting over similar bogs in northern France.

Over 85,000 dried sphagnum dressings were assembled at Sheffield University Hospital, to send to field hospitals to draw out fluid and tiny pieces of shrapnel from wounds, dramatically improving survival chances for Ian’s soldier grandfather, among others.

Professor Ian Rotherham with Papillose bogmoss

Professor Ian Rotherham with Papillose bogmoss

A combination of air pollution, over-grazing and drainage for intensive 20th century agriculture reduced the moss species on Sheffield’s moors, said Ian, but now pollution has reduced and grazing and farming practices are changing, and tiny moss spores carried by high altitude winds from Scotland and Cumbria (and potentially even the USA) are recolonising our moorland. There are even ‘hybrid’ mosses appearing, as gaps in the ecosystem are filled by potentially new varieties: Paul may have identified one such species for the first time on Sheffield’s moors.

The current consultations about the city’s flood defences should include the mosses and peat of Ringinglow Bog (owned by the council) and other wet local moorlands, said Ian.

Allowing nature to ‘roughen the catchment’, as it is already doing on the slopes above Ringinglow village, is part of the solution, he said, but disrupting or blocking drainage on moors and farmland would also help. Changes in farming grants could also allow farmers to reduce sheep numbers, plant trees and allow pastures to become wetter.

Sets of straw bales placed in upland moorland valleys would hold water on the moors, and would cost a lot less than engineering solutions in local parks, Ian said. And ‘roughening the catchment’ increases moss coverage and peat formation, and so becomes an even bigger sponge over time.

Professor Ian Rotherham (right) and Dr Paul Ardron examining mosses near Ringinglow Bog

Professor Ian Rotherham (right) and Dr Paul Ardron examining mosses near Ringinglow Bog

“These mosses are mopping up carbon, and mopping up water and holding water back. By the time the water reaches places like Endcliffe Park, the horse has bolted. It seems obvious to me you should be stopping water getting there in the first place.”

Visit UKeconet for more information about moss identification workshops and training.