Increased nutrients such as phosphorus and nitrogen can speed up the growth of algae causing a significant impact on the ecology of the river, a process called eutrophication. The sources of these nutrients generally include sewage treatment works, agriculture and septic tanks. This pollution is damaging to the wildlife of the River Dee, and steps to reduce nutrient pollution are necessary for the wildlife of the river to recover.

In 2019, the European Court of Justice (Dutch nitrogen case) pronounced that nutrient pollution must be considered as part of any habitat regulation assessment for new projects and plans which are likely to have an impact on a protected site (such as the Dee Special Area of Conservation (SAC)). In 2021 the UK’s Joint Nature Conservation Committee changed its guidance, leading to new tightened nutrient pollution targets for water-based protected areas including the River Dee SAC. Currently, only a few tributaries of the Dee have phosphate levels higher than the targets, but many tributaries are close. Tighter targets and a requirement for mitigation are great news in securing the long-term health of the River Dee and its tributaries, ensuring increased development in the catchment does not mean more damaging phosphate pollution.

This has an impact on planning permission for projects which add additional phosphorus to the Dee catchment, including those tributaries which are not part of the SAC but flow into the river. In practice, this means developments which add either additional sewage to treatment works or additional livestock to a farm. These developments need to offset their additional phosphate by creating a reduction elsewhere, a development can then be called nutrient neutral.

In Wales, Natural Resources Wales is recommending planning authorities do not grant permission unless developments are proven to be phosphorus neutral and have no additional impact on the River Dee SAC. This is not the case in England where Natural England is not recommending a need for nutrient neutrality to planning authorities.

The methods for reducing phosphate from other sources are now being considered but are likely to include changes to agricultural practices, reduction in clean water entering sewage treatment works or using wetlands to lock phosphate away in perpetuity. To get planning permission, developers will need to fund some of this work to mitigate the additional phosphate added by their proposals. This mitigation is creating a natural capital market for phosphorus mitigation within the Dee catchment.

At Welsh Dee Trust we are pleased these new stricter targets have come into place and that the impact on the river will be considered during planning permission. The challenge now is to make sure workable solutions are found that allow development to take place while protecting the long-term health of the river.

Welsh Dee Trust is already undertaking a wide variety of projects which are reducing the volume of phosphate in the Dee. We are working with developers and local authorities to ensure solutions are put in place which allows development to proceed without impacting the river. There are three guiding principles we believe should be incorporated into any phosphorus mitigation project.

• All phosphorus mitigation options need to go above and beyond legal pollution regulations.
• Calculations of total phosphate created from a mitigation project are based on the minimum confidence levels, not averages. This ensures all new developments using phosphate mitigation projects are truly mitigating their phosphorus.
• Each phosphorus mitigation project should include 20% of the total phosphate not used for mitigating development to ensure projects are not nutrient neutral but nutrient negative.