Watercourses provide essential ecosystem services including supporting native plant species, marine animals and their habitats, biodiversity conservation, and recreational purposes. Therefore, to preserve these functions, some watercourses are designated as Special Areas of Conservation (SAC) and Sites of Special Scientific Interest (SSSI) under the Habitats Regulations.

Nevertheless, human activities have increased the number of nitrates and phosphates in watercourses within the UK. Water run-off from agriculture including the use of fertilizers for plant growth and livestock farming, and effluent from sewage and wastewater from buildings have been major sources of nutrient pollution in designated watercourses. Consequently, the Department for Environment, Food and Rural Affairs (Defra), and Natural England have identified 27 catchments in 74 local planning authorities where designated river catchments have been shown to have nutrient pollution exceeding acceptable limits and for which nutrient mitigation measures must be implemented urgently.

Given the exigency of the situation and the need to prevent further nutrient pollution, local planning authorities within the affected catchments have been advised to ensure that the issuance of planning permission for new development should be based on the development being nutrient neutral. The implication of this advice is that to secure planning permission, new housing developments must show that their development would be nutrient neutral and where this is not possible, the developer must provide nutrient credits purchased from nutrient credits markets such as the Solent Catchment Nutrient Market or a nutrient mitigation project which will offset the expected nutrient pollution from the proposed development. This requires the introduction of nutrient mitigation strategies and schemes by the local authorities to support new developments.

However, despite the advice from Defra and Natural England, there is no integrated national strategy or legislation to support the development of nutrient mitigation schemes. An attempt by the government to remove the nutrient neutrality obligation on housing development was rejected by the House of Lords as this would have had adverse effects on the affected watercourses. The introduction of the nutrient neutrality obligations and the lack of adequate nutrient mitigation strategies and schemes in the affected catchments threatens the Government’s plan of 300,000 new housing projects annually.

Consequently, relevant stakeholders such as local planning authorities, Defra, Natural England and housing developers are faced with the dilemma of protecting designated watercourses from nutrient pollution and supporting the development of new housing to meet increasing demands. This dilemma is not helped by the lack of clarity at the strategic level. Nevertheless, the Environmental Geoscience and Hydrology (EG&H) Team in WRc has developed a number of solutions to help balance this dilemma by offering bespoke services to local planning authorities and housing developers in their efforts to mitigate nutrient pollution in designated watercourses whilst also ensuring that new housing developments are nutrient neutral.

Some of these services include:

• Preparation of Nutrient Mitigation Plans for both onsite and offsite mitigation projects;
• Nutrient mitigation project optioneering;
• Feasibility studies for nutrient mitigation projects e.g. Sustainable Drainage Systems (SuDS) and constructed wetlands;
• Calculation of nutrient budgets for new housing developments;
• Nutrient mitigation project monitoring;
• Monitoring water quality at mitigation projects; and
• Monitoring housing developers’ nutrient mitigation projects to ensure compliance with planning conditions.

Although there is still need for regulatory clarity regarding housing development nutrient neutrality obligations, the passing of the Levelling Up and Regeneration Act 2023 has introduced new nutrient pollution standards for some water companies set to take effect on 1 April 2030. These new obligations which are aimed at reducing nitrogen and phosphorus pollution in watercourses from wastewater treatment works (WWTW), imposes a duty on water and sewerage companies to upgrade their WWTW to meet set standards. Consequently, WRc is currently consulting with stakeholders to develop a forum to address the concerns of water companies. So, watch this space!