At Bere Marsh Farm in Dorset, we're harnessing the power of both technology and nature to ensure that the sewage from our buildings is as clean as possible before it reaches the adjacent stream or the River Stour.

We’re doing this using a new state-of-the-art sewage treatment plant, plus a filtration pond that will further remove nitrates and phosphates from the treated effluent.

The creation of the filtration pond has been funded by Wessex Water as part of its River Stour Phosphorus Reduction Scheme.

The farm already had a treatment plant, but it was old and needed replacing. The new plant has greater capacity, so it will be ready for future plans for the farm including the refurbishment of barns to provide better facilities for events and an increased number of visitors.

Once the sewage has been cleaned in the treatment plant, the liquid discharged flows into a shallow scrape (the filtration pond), where it percolates through plants and soil. This removes more nitrate and phosphate.

 For the majority of the time there will be no direct discharge of liquid from the plant into the adjacent stream, so the amount of these nutrients entering this watercourse and the River Stour will be greatly reduced.

Why high nutrient levels are a problem

High levels of nitrate and phosphate act like fertiliser when they exceed natural ‘background’ levels in streams, rivers, lakes and shallow coastal waters such as Christchurch Harbour, where the Dorset Stour reaches the sea. The result is algal blooms and oxygen depletion as the algae die and are degraded by bacteria. This is known as eutrophication, and in extreme cases can result in dead zones where fish, crayfish, riverfly larvae and other species cannot survive.

Many of Britain’s waterways are now affected by eutrophication, with farming and sewage being the two main sources of both nitrate and phosphate. Water companies, working with other organisations in river catchments, are now supporting a variety of schemes to reduce the problem at source. The River Stour Phosphate Reduction Scheme is an example of this collaborative work.

Putting the marsh back into Bere Marsh

In addition to the filtration pond, Wessex Water is funding work that will be carried out by the Wessex Rivers Trust to identify how drainage might be altered so that some of the fields on Bere Marsh Farm lie wetter for longer. This will also help to remove nutrients from water that flows through the farm from elsewhere, as well as improve the floodplain grassland habitat for plants, birds and insects that need damp ground.

Tim Stephens, Catchment Partnerships and Delivery Manager for Wessex Water, explained: “As part of Wessex Water’s River Stour Phosphorus Reduction Scheme we are pleased to be able to support the CRT and Wessex Rivers Trust with carrying out feasibility studies for wetland creation and floodplain restoration opportunities on Bere Marsh Farm. Managing the flow of water through the landscape to enable sediment removal and nutrient uptake by vegetation is a key strategy for reducing phosphorus pollution of our precious waterways.

“Our support for a filtration pond to treat water leaving the built area of the Bere Marsh Farm site should further reduce nutrient loading on the River Stour.”

CRT Chair Sue Everett said: “The River Stour is struggling with high levels of nutrients entering the watercourses and affecting water quality, so partnership projects that bring together landowners, conservation organisations, water companies and government agencies to reduce this through catchment sensitive farming and other interventions are vitally important.

“We hope the filtration pond will provide farmers and landowners with an inspiring example of the kind of method that can be used to reduce the amount of nutrients entering watercourses.

“Thank you to Wessex Water for its funding for the filtration pond and for supporting the next stage of research for our wider plans for Bere Marsh Farm.”

TOP: A female emperor dragonfly laying eggs (ovipositing) © Ben Stoney

ABOVE RIGHT: The new sewage treatment plant and filtration pond were installed by Environmental Drain Services, an experienced local firm, at the beginning of July © Elaine Spencer-White

ABOVE LEFT: This common mayfly is just one of the many species that needs clean water to complete its lifecycle © Nick Dobbs

Published: 27th July 2023