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Nutrient neutrality

Natural England's assessments during 2019/20 suggest that more than 3000 hectares of the intertidal parts of Chichester Harbour, which is the subject of several European designations, is now classified in an "unfavourable - declining" condition.  Natural England's Condition Review of Chichester Harbour sites (opens new window) was published in February 2021. 

Water quality is a contributing factor to the build-up of excess nutrients in the Harbour causing eutrophication (algal growth) which impacts on the Harbour's ecology and conservation.  Sewage from new development using waste water treatment works or an on-site package treatment plant that discharges to Chichester Harbour contributes to the excess nutrients in the Harbour (albeit in small amounts relative to other sources) and therefore needs to be considered in line with the Habitats Regulations.  This means that before agreeing to a proposal (such as a planning application or a development plan) the authority needs to undertake a Habitats Regulations Assessment and be satisfied that the proposal will not have any adverse impact on the protected site or sites.  Certain types of new development will now need to be nutrient neutral to avoid detrimental harm to the Harbour's ecology and conservation.  


Natural England published detailed guidance on achieving nutrient neutrality in June 2020 which included a methodology for calculating the "nutrient budget" of proposed development. 

In March 2022 and more recently, in February 2024, Natural England updated their advice and guidance for calculating the nutrient budget.  This advice is based on the most up-to-date scientific information regarding water quality and so must be taken into account in preparing Habitats Regulations Assessments on planning applications.

As part of the information needed to determine planning applications, if a relevant proposal (primarily those involving an overnight stay) is likely to discharge into Chichester Harbour, then a nitrogen budget will need to be prepared and submitted with the planning application.  Natural England's Guidance sets out when and how nutrient neutrality must be achieved with catchment maps to clarify the areas that are affected.

Natural England's new advice can be found on the Government's website (opens new window) which includes the Solent nutrient neutrality calculator as well as Guidance (opens new window) on how to use the calculator.

The Government issued a Ministerial Statement (opens new window) on 20 July 2022 pledging a package of further measures to tackle nutrient pollution including tabling an amendment to the Levelling Up and Regeneration Bill to place a new statutory duty on water and sewerage companies to upgrade wastewater treatment works in nutrient neutrality areas, as well as supporting Natural England to establish a Nutrient Neutrality Strategic Mitigation Scheme.  Further details will be announced by Natural England in the Autumn. 

CIRIA have recently published guidance for Sustainable Drainage Systems (SuDS) (opens new window) reducing nitrogen in surface water runoff. This guidance can be utilised by developers both at the outline and detailed design phases of developments that fall under the current nutrient neutrality guidance for the Chichester Harbour catchment. This guidance documents can be used to calculate the nitrogen load that can be removed from various SuDS treatment systems and trains. This calculated reduction in nitrogen can then in turn be used to reduce nutrient loads from proposed developments. Please note that the reduction can be applied at stage 3 of the nutrient budget calculations. Any residual nitrogen not removed from SuDS, can then progress to stage 4 of the calculator, where a precautionary 20% buffer will be applied.

The Rivers Trust and Constructed Wetland Association have set up a Constructed Wetlands Hub (opens new window) where specific details around designing and constructing wetlands for nutrient neutrality can be found.  In particular, the Natural England Framework for Wetland Mitigation Proposals has been produced by Natural England working with the Rivers Trust and the Constructed Wetland Association, to guide anyone interested in submitting a proposal for wetland designed to deliver nutrient neutrality.

Framework Approach for Responding to Wetland Mitigation Proposals (PDF) [2MB]

Southern Water has produced a helpful infographic providing a broad overview of the issues of nitrates in Chichester Harbour, and this is also available to view.

Southern Water - Protecting Langstone and Chichester Harbours from nitrogen pollution (PDF) [260KB]

Joint working

We are a working with the Partnership for South Hampshire (PfSH) and other authorities affected by the issue of nutrients through the PfSH Water Quality Working Group. In light of the advice from Natural England, one of the key areas of work that the PfSH Water Quality Group is currently focused on, is nutrient mitigation.  PfSH publish a list of currently available potential nutrient mitigation schemes (opens new window).

PfSH and other affected authorities, including Chichester, have together employed a Strategic Environmental Planning Officer (SEPO) whose primary objective is to provide a strategic response to the issue of nutrient neutrality across the impacted areas of the Solent.  As well as providing a single point of contact to the development industry and landowners who may be able to offer mitigation solutions, the SEPO monitors the supply and demand relating to nutrient neutrality mitigation and engages with stakeholders to facilitate mitigation schemes coming forward to satisfy demand.  The SEPO also aims to promote consistency between local planning authorities regarding the legal process required to secure mitigation through the planning process. The SEPO's progress is reported in a newsletter (opens new window).

The Solent nutrient market pilot project seeks to develop and trial a nutrient trading process, testing the feasibility and costs of a market-based approach to trading nutrient credits, and exploring how multiple benefits can be delivered. The pilot is being led by DEFRA, working with Natural England, the Partnership for South Hampshire and other partners including the Department for Levelling Up, Housing and Communities, Environment Agency and Forestry Commission. 

Further details including FAQs for nutrient credit suppliers and developers is available from the PfSH Defra Trading Platform (opens new window) webpage whilst a project update and helpful infographics explaining the need for nutrient neutrality, how the trading platform works and the landowner process are available below.    

Solent Nutrient Market Update December 2021 (PDF) [304KB]

Solent Nutrient Trading Pilot Project Update Sept 2021 (PDF) [291KB]

Solent Nutrient Trading Pilot Overview and Impacts Infographic (PDF) [438KB]

Solent Nutrient Trading Pilot Landowner Process Infographic (PDF) [507KB]


Contact us

For further information and advice email Alternatively, you can phone us on 01243 534734.

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