What is nitrogen pollution and mitigation in Poole Harbour?
Poole Harbour is defined as a Special Protection Area and Ramsar site which is protected by the Habitats Regulations. Sites which are protected by the Regulations are important for nature or protecting threatened habitats and species. The regulations require the councils to assess environmental impacts of plans (including local plans) and projects (including planning applications) on these sites. The councils may only grant planning permissions that will not adversely affect a protected habitat site or ensure that any adverse effects are mitigated. As part of the decision-making process the councils are obliged to get advice from Natural England.
High levels of nitrogen discharged into Poole Harbour has caused increases in algal growth with resulting losses in biodiversity. An overall reduction is needed to bring the harbour back into a favourable condition. Agriculture is a significant contributor to nitrogen loading and schemes like the Poole Harbour Nutrient Management Scheme (PHNMS) have been set up to address this. Nitrogen in treated waste effluent from sewage plants also contributes to the pollution effecting the harbour. Planned upgrades at Wastewater Treatment Plants will deliver improvements over the long term. In the short term before the condition of the harbour is improved, any new development which contribute to nitrogen pollution must demonstrate nitrogen neutrality (this means demonstrating that there is no net increase in nitrogen discharged into the harbour after new development is occupied). Typically, nitrogen neutrality is achieved by reducing nitrogen loading on the harbour elsewhere in the catchment to offset the impacts of development.
A map showing the extent of the Poole Harbour Catchment (PHC) can be found on the last page. All mitigation needs to be delivered within the catchment boundary.
It is the responsibility of Dorset Council and Bournemouth Christchurch and Poole (BCP) Council as the planning authorities to assess the impact of planning applications and plans on the harbour to ensure there are no negative effects. Where it is not possible to deliver mitigation on development sites, developers will need to investigate other options (potentially including working with other third-party providers) to deliver the necessary nitrogen reductions equivalent to the increased loading from their development proposal. The councils have also committed to working together to invest a government grant to deliver projects to provide another mitigation option for developers.
The council would like to work with farmers and landowners in the catchment to help identify and fund appropriate mitigation projects. This mitigation may take several different forms and could be both temporary or permanent.
The upgrade of wastewater treatment works through the Levelling Up and Regeneration Act 2023 will improve the performance of certain wastewater treatment works (WWTW) to achieve a higher permitting requirement (known as a technically achievable limit) by April 2030. For developments linked to a WWTW where upgrades are anticipated, the mitigation requirement will decrease after 2030. Therefore, there may be an option to provide land-use change that delivers temporary mitigation only.