Nutrient neutral development

On 26 January 2024, Natural England released new calculators for completing a nutrient budget. Guidance remains on how development with the potential to have nutrient impacts on Habitats sites should now be considered when making planning decisions.  For all planning applications that have a condition yet to be discharged, we will use the new calculators to carry out nutrient budgets for new development within the plan area, but dwelling or accommodation occupancy rates will need to be adjusted from the calculator defaults.  See the 'Achieving nutrient neutrality' section below for further information.

Development in areas with nutrient-rich water must mitigate its effects and provide a nutrient-neutral environment.  

Evidence has shown that residential development contributes to high levels of nutrients in the water environment, specifically nitrates in Solent catchments and phosphates in the Avon catchment. Adverse effects on international nature conservation sites in the Avon and Test river catchments cannot be ruled out. The full list of affected European Sites can be found in Policy ENV1 of the Local Plan, but please note this website reflects the latest Natural England advice including changes since the Local Plan was adopted in 2020.

The extent of nutrient enrichment causes an excessive growth of plants and algae, known as eutrophication, which reduces the oxygen content in water. This process makes it more difficult for aquatic insects or fish to survive, in turn removing a food source from the food cycle for protected species such as wading birds and salmon.

Following recent case law, residential and other development providing overnight accommodation will need to mitigate its effects to become nutrient-neutral, to avoid making the current situation worse. Adverse effects arise from increased sewerage treatment, and from surface water run-off from both urban and greenspace areas.

A nutrient avoidance and mitigation package will be needed to achieve nutrient neutral development before a planning permission can lawfully be issued in accordance with The Conservation of Habitats and Species Regulations 2017.

Affected areas

The Nutrient Mitigation map shows the areas within New Forest District Council that are required to achieve nutrient neutrality. If your development is within this area, it is important you follow the requirements.

You can download a map below showing the nutrient mitigation areas.

Nutrient Mitigation Areas Map (PDF) [3MB] (opens new window)

* Check with the water company and Environment Agency whether a mains sewer connection is available or practicable.  If not, mitgation requirement calculations should be based on a septic tank/packet treatment plant system.

Evidence supporting mitigation schemes based in NFDC

For mitigation projects in NFDC evidence of their suitability and efficacy can be accessed below.

Phosphate mitigation options assessment (PDF) [2MB]

For mitigation proposals based outside NFDC equivalent documentation will be available from the host local planning authority.

Nutrient avoidance, mitigation and offsetting

The Mitigation Hierarchy is the accepted national approach to managing harmful impacts on biodiversity.  Avoidance of any impacts should be the first consideration.  The next step is on-site mitigation of any impacts that cannot be avoided.  The last step is compensation measures in an off-site location to offset any unavoidable remaining impacts.

The avoidance and mitigation package for nutrients should start at development master planning stage with avoidance and mitigation measures to manage surface water run-off.  This will need to be demonstrated through the planning application process.  The aim should be to achieve run-off neutrality wherever possible (and a credit where practicable), to minimise the extent of offsetting required for the main source of additional nutrients, foul drainage.  

Construction Industry Research and Information Association (CIRIA) guidance C808 Using SuDS to reduce phosphorus in surface water runoff (December 2022) explains how SUDs design can mitigate at source environmental impacts from phosphorus on the water environment.  Equivalent CIRIA guidance for mitigating nitrogen in run off is expected during 2023.

Nutrient offsetting credits

In most cases on-site mitigation will not be enough and additional off-site offsetting measures will also be required. Off-site measures may include:

• The purchase of nutrient offset 'credits' from an appropriate body (such as those listed as providers in the table above, or in due course from the Solent nutrient trading platform currently being set up by DEFRA).   Credits are made available in return for a financial contribution paid by the developer to implement the approved mitigation scheme.  
• Bespoke mitigation projects prepared by the developer.   Projects should be discussed with the Council at pre-application stage, following which Natural England's Developer Advice Service must be used to confirm that the projects will provide effective mitigation in perpetuity.

Planning application requirements

As part of the information needed to determine relevant planning applications, a European Site avoidance and mitigation checklist will be required. You can download this document below.

European site avoidance and mitigation checklist (PDF) [406KB] (opens new window)

Achieving nutrient neutrality

The latest tools and guidance issued by Natural England to enable nutrient neutrality to be assessed and implemented as a potential mitigation solution can be downloaded below.

Please note that in each calculator you will need to amend the average occupancy rate on the Stage 1 tab based on the mix of your development using the figures in the table below. You can calculate the average occupancy using our Average Occupancy Calculator (Excel doc) [11KB]

Solent Nutrients

Solent Nutrient Budget Calculator (Excel doc) [147KB]

Solent Nutrient Budget Calculator Guidance Document (PDF) [796KB]

Nutrient neutrality principles (PDF) [147KB]

Nutrient Neutrality Generic Methodology (PDF) [899KB]

Solent map SSSI (PDF) [2MB]

The new calculator and guidance for the Solent still allows Deductible Acceptable Loading (DAL) to be accounted for in nutrient budget calculations, but now only if the water supply to the development comes from within the catchment of the European site(s) affected by nutrients in wastewater (for example, where water supply to the development originates from within the Solent catchment - this is explained on p12 and 13 of the Solent guidance).   

Developers are advised to confirm which water company will supply their development with drinking water before completing the nitrates calculator.  Note that wastewater treatment may be provided by a different water company.

The DAL should be set to 'Yes' wherever drinking water is supplied by Southern Water, likely to include all of the Totton and the Waterside sub-area.  The DAL should be set as 'No' where drinking water is supplied by Bournemouth Water, likely including all of the South Coastal Towns sub-area.

River Avon Nutrients

River Avon Nutrient Budget Calculator (Excel doc) [102KB]

River Avon Nutrient Budget Calculator Guidance Document (PDF) [796KB]

River Avon map SAC (PDF) [1MB]

Dwelling occupancy rates in NFDC

Pages 7 + 8 of Natural England's "Nutrient Neutrality Generic Methodology" (Issue 1 February 2022) states that a local average occupancy rate can be used, providing that it is supported by robust and sufficient evidence. A range of occupancy figures have already been used by us in the production of its Local Plan (Adopted 2020) and in the previous versions of the nutrient budget calculators.

Applications will need to calculate a single occupancy figure and enter it into Stage 1 of the revised calculator.

For residential planning applications in our planning area the following occupancy rates will be applied, consistent with the approach for mitigating the recreational impacts of new housing on the New Forest European sites.

The unspecified dwelling size assumes a housing mix compliant with 6.1 of Policy HOU1 in the Local Plan 2016 - 2036 Part One: Planning Strategy

For outline planning permissions, at detailed application stage we will require that the nutrient budget for the site be recalculated for the actual dwelling mix and layout. Depending on the final unit mix the number of dwellings that can be accommodated may change from the figure in the outline permission.

Other forms of overnight accommodation

Units of visitor or institutional accommodation, or other proposals that include overnight stays including campgrounds, will be calculated on a dwelling-equivalent basis.

As a starting point the occupancy rate for a studio/1-bed dwelling will be applied to a hotel, guesthouse, care home 'room' or a campsite pitch. Relevant and robust evidence on rates of occupancy, including seasonal variations or periods of closure, will be taken into account.

Redevelopment of existing residential or visitor accommodation sites

Nutrient mitigation is likely to be required for a redevelopment if the number of residential or accommodation units (homes, rooms, camping pitches etc.) increases.

An allowance will be made for the nutrient impact of the existing development, and only the net additional nutrient impact will need to be mitigated.

The mitigation requirement for the new development should be calculated using the relevant nutrient calculator.   Then calculate what the requirement would be for the existing development (as if it was a new development), and deduct this amount from the 'new development' total to provide a net additional figure.

Typically, nutrient migiation will not be required for replacement dwellings or extensions.

Permitted development rights and compliance with the Habitats Regulations

The General Permitted Development Order (GPDO) allows for the change of use of some buildings and land to Class C3 (dwellinghouses) with this development subject to a prior approval process. However the Habitats Regulations also apply to such developments.  We are obliged by the regulations to assume that there will be a significant effect on the New Forest and Solent SPAs.

Any development for prior approval should also be accompanied by an application for us to do a Habitats Regulations Assessment on the proposed development (please note there is a £30 fee for this). The development will need to include a mitigation package to mitigate the significant effect on the New Forest and Solent SPAs which new residential development would otherwise result in.