pH balancing trial could create healthier river for Dartmoor fish

From left: Dr Richard Sandford (Lecturer in Environmental Science – University of Plymouth), Dr Sean Comber (Associate Professor in Environmental Science - University of Plymouth) and Dr Bruce Stockley (Head of Fisheries and River Management at the Westcountry Rivers Trust)

The University of Plymouth is working with the Westcountry Rivers Trust to trial a new approach to balancing the pH of the upper river Dart.

Together, the research team hopes that the study will find a practical way to create a healthier environment for salmon and other aquatic life.

This collaborative project, involving jointly funding a research project, brings together the stakeholder engagement and environmental management experience of the Westcountry Rivers Trust and the analytical chemistry and ecological expertise of the University of Plymouth to tackle this significant environmental issue.

Salmon in the West Dart are classified as being ‘at risk’ and one of the causes of their decline is believed to be the harmful effects of historic acid rain. By introducing mesh bags containing local calcium carbonate to the river, the team aims to reduce the acidity of the river, returning it to its natural pH levels.

The trial will focus on a small tributary near the head of the river in a remote area of west Dartmoor. After adding the calcium carbonate from a local quarry near Ashburton, the researchers will continually monitor the river’s chemistry and aquatic life via in situ monitors.

The trial follows in-depth research and input from stakeholders including the Duchy of Cornwall, Dartmoor National Park, South West Water, Environment Agency, Natural England and the local farming community.

Dr Bruce Stockley, Head of Fisheries and River Management at the Westcountry Rivers Trust said:

“Despite having very clean water, the West Dart has problems with survival for salmon. One of these causes is thought to be the fact that the river is now unnaturally acidic, as a result of historic pollution. pH readings for the West Dart are acidic and regularly below 5, which is dangerously low for fish. Our research has shown that, unfortunately, natural recovery from acid rain for upland moors will take decades, and without help some areas may never recover.
“Introducing calcium carbonate to balance a river’s pH level is common practice in many parts of the world, particularly in Scandinavia. This is a small pilot project, but its findings will have a big impact if we discover this approach could help salmon and other river-life on Dartmoor. We’re delighted that so many environmental organisations and local interest groups have come together to try to find a practical solution to a very real problem.”

During the three-year trial, University scientists will assess the impact of the calcium carbonate on the chemistry of the river and its resident invertebrates. While the impact on salmon could take a number of years, the data will indicate whether or not the trial has successfully balanced the river’s pH levels.

Dr Sean Comber, Associate Professor in Environmental Science at the University of Plymouth said:

“Using a combination of spot sampling and data loggers we will be monitoring the water quality and ecology to assess immediate and long terms impacts, hopefully leading to a recovery of the fragile ecosystem.”

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