‘Sacrificial’ manmade wetland is key to cutting river pollution
Strict targets to reduce contamination from treatment works are forcing water company bosses to turn to the power of nature
Building a wetland and deliberately pumping effluent from a sewage works into it might seem like a strange way to clean up a river.
Yet that is exactly what conservationists funded by a water company have done in Norfolk, in a trailblazing scheme that could be emulated across the country. Behind a hedge outside the village of Langham, in a field until very recently grazed by cattle, lie three newly dug “cells” where rushes, marigolds and sedge are growing.
On the other side of the hedge is a small sewage treatment works run by Anglian Water, which previously released effluent straight into a stream that runs into the River Stiffkey, one of Britain’s globally rare chalk streams. Now, the treated water is released into the wetland, where the plants gradually strip out phosphates, a form of nutrient pollution that in excessive levels creates algal blooms that choke fish in rivers.
“It’s a little bit sacrificial,” admits Dr Jonah Tosney, technical director at Norfolk Rivers Trust. “We’d rather have a pristine wetland but it’s not realistic with the population pressure we’ve got.”
About the size of a hectare, the “constructed wetland” is a response to a new urgency to cut phosphate pollution. Last year the government set an ambitious and, more importantly, legally binding Environment Act target of cutting phosphorus from wastewater treatment works by 80 per cent by 2037.
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Anglian Water was among several private water firms that lobbied against the government goal, arguing that it risked “driving up additional costs for customers”. However, now the target is the law, the firm sees constructed wetlands as a key tool for meeting the deadline.
The advantage of wetlands like this one, which were visited by a heron and pair of swans when The Times was there, is that they offer a way to improve water quality while boosting insects that birds feed on. The Langham wetland is on private land inaccessible to the public, but future wetlands could have footpaths to open them up for recreation too.
They are also relatively cheap. Building a conventional phosphorous-stripping works next to the existing Langham treatment plant would cost about £1 million a year, and about £100,000 a year to run. By contrast, the wetland cost about £250,000 and then £10,000 annually to maintain.
The flipside is that in some cases wetlands won’t be able to get phosphate levels low enough to meet targets, when compared with chemical and biological methods. Even more challenging is the availability of land.
The Times launched its Clean It Up campaign this year, calling for a series of measures to help improve the country’s rivers and seas.
Tosney said the landowners at Langham are losing money but saw it was “the right thing to do”. That’s hard to replicate if you want to scale up wetlands. “It isn’t going to happen very often,” he said. Farmers have plenty of alternative options for income, from the government’s new farming subsidies for helping wildlife to reducing their pollution into rivers to earn valuable credits and sell them to housebuilders.
Nonetheless, Anglian Water hopes to build 26 wetlands over an area the size of 100 football pitches by the end of this decade. Carly Leonard, head of environment strategy, said: “The alternative to doing this is additional treatment on the back of these recycling centres [treatment works], which is a cost to the environment, a cost to customers, a cost of carbon emissions. So this is very much the way that we want to be working in the future.”
One tool the company hopes will help is working with Microsoft to build a “digital twin” of catchments, creating virtual versions fed with weather and data from sensors measuring phosphate levels, temperature and more. The firms have started on the Stiffkey but set their sights on the far bigger catchment of the River Wensum, which runs through Norwich. In theory, the digital twins could provide evidence that makes the case for more Langhams.
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If better rivers, which The Times’s Clean it Up campaign has called for, do not prove enough of an incentive for further wetlands, their ability to curb flood and drought risk could be.
The headwaters of most chalk streams are “hydrologically knackered”, said Tosney, who sees more wetlands as a key solution. “The headwaters should be holding water and releasing it really slow. We shouldn’t be getting floods and droughts, it should be a steady release of water,” he said.
The Times is demanding faster action to improve the country’s waterways. Find out more about the Clean It Up campaign.
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