Poole Harbour is designated as an SPA and Ramsar. Within the Poole Harbour catchment, mitigation has been delivered since 2017 through the Nitrogen Reduction in Poole Harbour Supplementary Planning Document (SPD) (April 2017). It is not considered appropriate to continue to use the SPD as the approach to calculating nutrient loading and mitigation requirements is no longer consistent with the up-to-date understanding of nutrient pollution.
When Natural England updated their advice for the Poole Harbour catchment in March 2022, phosphorus was added alongside nitrogen as nutrients of concern. After this announcement planning decisions on development proposals where an increase in nutrient loading was likely could only be granted if the proposal included appropriate phosphorus mitigation. On 25 January 2024, the Secretary of State designated Poole Harbour as a nutrient sensitive catchment for both nitrogen and phosphorus.
The measures included in the Levelling Up and Regeneration Act that require the upgrade of wastewater treatment works will reduce the nutrient concentrations in wastewater and the mitigation burden for developments. Additionally for phosphorous pollution within the Poole Harbour catchment, following the list of exemptions from government that was issued on 24 May 2024, Natural England have advised us that sufficient wastewater treatment works will be upgraded to reduce phosphorus levels beneath a threshold so that there is no longer a need for development to deliver phosphorus mitigation.
Mitigation and the Local Nutrient Mitigation Fund
Dorset Council has been awarded £4.63m of grant funding from government to aid the delivery of nitrogen mitigation within the Poole Harbour catchment. This will enable both Dorset Council and BCP Council to identify and deliver mitigation projects and to sell nutrient mitigation credits for qualifying developments. The receipts from the sale of these credits will be reinvested to deliver further nitrogen mitigation projects.
In the Dorset Council area developers now have the responsibility for securing nutrient mitigation for their development proposal. Mitigation can be secured:
- on-site or through land in the ownership of the developer
- through an agreement with an accredited third-party mitigation provider
- through an agreement with Dorset and BCP Councils when acting as mitigation providers
In all instances, the mitigation will need to be secured in perpetuity through the necessary legal agreements or planning condition.
Decision making in the Poole Harbour catchment
Within the Poole Harbour catchment, there is a need for qualifying developments to demonstrate neutrality for nitrogen. Qualifying development includes:
- any form of development that increases overnight stays within the catchment
- some commercial development that either attract large numbers of people into the catchment (such as a tourist attraction) or where there is a significant discharge into the catchment for example from an industrial process
- development which results in the intensification of agricultural practices, such as an additional cattle barn
Development that increases overnight stays in the catchment may comprise permanent residential development, gypsy and traveller development, care homes, nursing homes, tourist accommodation including both permanent and temporary campsites and hotels.
The boundary of the Poole Harbour hydrological catchment is shown on Dorset Explorer and Wessex Water’s wastewater management plan map provides details of the areas served by their wastewater treatment works and where treated wastewater effluent is discharged. Within these areas, it is presumed that wastewater and surface water arising from qualifying development is likely to increase nutrient levels within Poole Harbour. Where an applicant considers that either wastewater or surface water from their development will not discharge into Poole Harbour they must submit details with their planning application.
The Natural England nutrient calculator for the Poole Harbour catchment (May 2024) should be used to assess the development’s nutrient budget.
A nutrient neutrality statement must be submitted with any planning application for qualifying development in the Poole Harbour catchment in Dorset Council area. There are further details on the statement in our local list requirements, but it should include:
- an assessment of whether the proposed development is also ‘qualifying development’
- details of arrangements for managing wastewater and surface water arising from the development
- a nutrient budget calculation for nitrogen made using the Natural England nutrient calculator for Poole Harbour
- details (including how this mitigation will be delivered and secured in perpetuity) of the mitigation proposed to offset nutrient loading
We have produced a guidance note to assist applicants where they propose to upgrade an existing septic tank or package treatment plant to provide mitigation measures, or where they propose to connect a development to a new package treatment plant. Where relevant, applicants may wish to refer to this note when preparing their planning application.
New approach to funding and delivering mitigation in Poole Harbour catchment
For all those planning applications determined after the 31 July 2024, applicants or developers for qualifying development in Poole Harbour’s catchment must secure nutrient mitigation for their development proposal. Mitigation can be secured:
- on-site, or through other land owned by the applicant or developer (as an example mitigation may include changes in land management to offset impacts or a new wastewater treatment works managed by a NAV water company)
- through an agreement with an accredited third-party mitigation provider
- through an agreement with Dorset and BCP Council acting in their capacity as a nutrient mitigation provider
In all instances, the mitigation will need to be secured in perpetuity through the necessary legal agreements or planning condition and details of the mitigation measures must be presented by the applicant or developer as part of their nutrient neutrality statement.