Civil Initiative Leads Efforts to Restore These Clear, Freshwater Ecosystems
Southern England is home to unique freshwater ecosystems known as chalk streams. The name is derived from the rivers’ unusual chalk bedrock, formed during the Cretaceous period.
Teeming with flora and fauna, England’s chalk streams are at risk from pollution, runoff, and other kinds of degradation. However, initiatives such as the Catchment Based Approach (CaBA) Chalk Stream Restoration Group is meeting the challenge of restoring these rare ecosystems.
Origins of Chalk Streams
Charles Rangeley-Wilson, chair of the CaBA Group, notes how chalk “accreted” or accumulated on the bed of the ocean over 60 million or 70 million years in very warm seas. A tiny, single-celled creature called coccolithophores, a type of phytoplankton, became encased in plating of calcium carbonate known as coccoliths.
These creatures “rained down onto the floor of the sea and formed a sort of deep porridge-like ooze, … and then that became chalk when the sea level retreated. … And then, by various forms of plate tectonic activity, those beds of chalk were forced to the surface,” he explains.
While some limestone may have been formed in a similar way, older forms have been buried under subsequent layers of geology, making it much harder as it comes under pressure, says Rangeley-Wilson.
“Chalk is very, very soft,” he states. “And it’s almost completely soluble. If you put a piece of chalk into a bucket of water, let it soak through, and then took it out and just exerted the tiniest pressure on it, it would just crumble to nothing. So, the glaciers obviously destroyed most of the chalk and washed it away, leaving behind the chalk hills that form our chalk streams.”
This makes chalk useful as a writing tool for chalkboards as well as in agriculture to change the soil’s acidity and as a construction material.
England’s Unique Chalk Streams
There are about 300 chalk streams in the world, about 85% of which are in southern England, says Stewart Clarke, PhD, who is with the National Trust, a CaBA Group partner, and is a specialist on national freshwater, catchments, and estuaries.
There are about 300 chalk streams in the world, about 85% of which are in southern England, says Stewart Clarke, PhD.
He credits the climate in the south of England and other parts of northwestern Europe, like northern France and Denmark, for creating the ideal conditions for chalk streams.
“You can go to lots of parts of the world where there is chalk, but the valleys tend to be dry,” he explains. Chalk streams emerge when “there’s enough water around during the winter months to give you that groundwater,” he says. “So, it’s a particular set of circumstances the chalk geology gives you in ... southern England, northern France, that creates this unique habitat, and that’s why they’re so rare globally.”
Havens of Biodiversity
Chalk streams have a distinct ecology. “In a natural situation, there’s this steady flow because the water coming out of the bedrock, [meaning] they tend to have a very even temperature regime,” says Clarke. As chalk streams are cool in summer but warm in winter, they can support certain species.
Clarke adds: “The filtering process also means that the water comes out very, very clean and very clear because it’s been forced through very tiny pores in the chalk bedrock.”
Because the water is clear, “lots of light gets to the bottom of the stream; we get plants like water crowfoot […] and now those plants growing submerged in the chalk stream create a set of habitat conditions in the river as well,” he says.
Salmon, brown trout and grayling, chub, barbel, roach, as well as the white-clawed native crayfish can all be found in chalk stream rivers. The habitat is also ideal for mammals, such as the water vole, otter, and beaver.
Clear, clean gravels are important for fish spawning and for invertebrates, like mayflies. Salmon, brown trout and grayling, chub, barbel, roach, as well as the white-clawed native crayfish can all be found in chalk stream rivers. The habitat is also ideal for mammals, such as the water vole, otter, and beaver.
Chalk streams are also carbon stores. The flood plains create the perfect conditions for the formation of peat, the remains of dead vegetation.
If peat dries out, carbon “gases off into the atmosphere,” but if it remains wet, carbon stays trapped within the peat, Rangeley-Wilson says.
Pollutants Endanger Chalk Streams
This rare ecosystem is in danger, however. Water companies are guilty of abstraction, which involves draining the rivers for purposes such as irrigation and drinking water.
Pollution is another problem. Clarke states: Treated and untreated sewage from water companies “is one part of a bigger picture around sewage. In rural areas, lots of people are not on main drainages.” Thus, the septic tanks that people have in their homes “can be contributing, if they’re close to the river,” he says.
As reported by BBC earlier this year, there are major concerns about sewage pollution in the River Kennet, one of England’s most important chalk streams and one of the largest tributaries to the Thames River.
Other pollutants, such as nutrients and sediment from agriculture as well as herbicides, also cause problems.
According to charity Wildfish Conservation’s 2021 Riverfly Census Report, about 26,200 tons of phosphorus are lost into the aquatic environment each year. Chemical pollution can form “an unknown, poisonous cocktail which can devastate freshwater biodiversity,” the report says. Sediment can also clog gills of fish, kill invertebrates and fish eggs, block out light, and bind to chemicals, causing them to remain in rivers for longer.
But that’s not all. Over time, rivers have been straightened and deepened, which means habitat variability has declined. Clarke says if rivers are altered, “you’ve effectively got a straight channel, just with water in it; you’ve got less opportunity for plants to take up and soak up nutrients.” And water is carried away much faster.
River Restoration Work
The CaBA Group has established an agreed-upon set of actions to tackle these problems in Norfolk and Lincolnshire. The communities, water companies, industry, the government, environmental regulators, and individuals are all involved.
Rangeley-Wilson claims: “The restoration work has to be three-dimensional. … You’ve got to address the water quality, the pollution, … the over-abstraction and … the fact that we’ve changed the rivers physically.”
Rangeley-Wilson claims: “The restoration work has to be three-dimensional. … You’ve got to address the water quality, the pollution, … the over-abstraction and … the fact that we’ve changed the rivers physically.”
For instance, in Norfolk, long sections of rivers like the Nar and Stiffkey have been moved from their channels and re-established as meandering rivers across the flood plain. In collaboration with Norfolk Rivers Trust, a 2-kilometer section of River Stiffkey was reunited with its floodplain in 2023, and results have shown improved numbers of fish and a diversity and abundance of insect and plant life.
Restoration work on the River Bure, also in Norfolk, included working with farmers to create a track to redirect silt-laden water into a silt trap. They then clean water through the installation of dams and an outfall pipe to collect and hold water, so sands and soil can “drop out.” Deadwood and overhanging vegetation were also removed to provide wildlife and plant habitat.
Elsewhere, Chalk Streams of Lincolnshire have been improving rivers around the Lincolnshire Wolds. The River Rase had been widened and diverted to power a water mill. Silt had eroded the banks, and there were overhanging trees. Recent restoration work involved narrowing the river by repairing the banks and protecting them with coir (fibrous material from coconut husk) matting, and introducing a chalk lining, along with a mix of gravel.
Volunteers Play a Key Role
Volunteers help create new channels using diggers, monitor water quality, and collect samples to build up a picture of the species living in the river—for example through the Riverfly Monitoring Initiative.
Volunteers help create new channels using diggers, monitor water quality, and collect samples to build up a picture of the species living in the river—for example through the Riverfly Monitoring Initiative.
Jade Oliver, who has volunteered at the Lincolnshire Chalk Streams project, says mornings consisted of conducting a Riverfly survey at one of the chalk streams in the Lincolnshire Wolds.
She adds: “Waders on, it’s time for a kick sample, after which we identify the invertebrates found to use as a guide to the chalk stream’s health.”
Oliver also logs in to images from night vision cameras to establish the whereabouts of mammals, such as the water vole and otter.
“One of my favorite things about volunteering is learning all about the amazing local wildlife found around our rare and beautiful chalk streams, teaching other people to love it too, and getting hands on and out and about in this incredibly varied and rewarding volunteer role,” she concludes.
*Yasmin Prabhudas is a freelance journalist working mainly for non-profit organizations, labor unions, the education sector, and government agencies.
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