Nitrates and the impact on designated sites

Nitrates have become a significant factor in the planning process for new development. 

In 2018 and 2019 Natural England conducted a number of assessments on the condition of designated sites in the Solent region. The results indicated a failing in the nutrient quality of the water due to the input of nitrogen and wastewater from housing and other development, impacting on the habitats of wetland birds and posing a risk to the protected status of the sites.

Since then, a number of local authorities in the Solent region have halted the issue of planning permissions whilst they consider how to mitigate against these impacts.

This insight looks at the recent advice from Natural England and provides an overview of the methods used to measure nitrogen output of new developments in the Solent region, and the steps that developers and landowners may need to take against the impact of new development on these designated sites.

The Concept of Nutrient Neutrality

The advice from Natural England focuses on the principle of “nutrient neutrality” which seeks to ensure that new development in the Solent region should not add to the “existing nutrient burden” on designated sites.

To calculate the impact of new development, local authorities use either recognised average figures provided by bodies such as Southern Water and the Office of National Statics, or bespoke figures (where there is enough evidence to support them).

The nitrogen burden from a proposed development is estimated using the following factors:

  • the increase in population as a result of the development
  • the estimated wastewater production from the development
  • the efficiency of the treatment works at removing the input nitrogen from wastewater.

Recognising the importance of the third factor, Natural England encourages local planning authorities to include pre-commencement planning conditions relating to the maximum water usage of the development.

Mitigation steps to achieve nutrient neutrality

If the calculation results in a positive figure, the development will add to the existing nitrogen burden. The following steps can be taken in order to reduce that burden to a nil value – this will be secured either via a planning condition or an s106 agreement:

  • Upgrading the sewerage treatment works
  • Taking land out of high nitrogen uses – such as agricultural land
  • Specific on-site/off-site provision:
    • On-site– increasing suitable alternative natural greenspace (SANGS) and open spaces;
    • Off-site – acquiring or supporting the acquisition of agricultural land elsewhere within an appropriate river catchment area to change its use either to woodland, heathland, saltmarsh etc. Note that the land must be acquired/secured at the time of the assessment to ensure performance (e.g. change of ownership to a local planning authority).
    • Woodland planting on agricultural land (achieving 20% canopy cover at maturity/ approx. 100 trees per hectare) which shall be secured as a permanent change in land use;
    • Wetlands - can be included within the sustainable urban drainage system, where run-off from urban areas can be discharged through wetlands or alternatively streams can be re-diverted through the wetlands.

    With smaller proposed developments, on-site options will be limited. Such schemes could therefore consider off-site measures such as the creation of a local pond, wetlands, nature reserve etc.

    In order for the mitigation to be effective, Natural England consider the mitigation land should be within the same river catchment as the proposed development location.

    The above measures aim to avoid the impact of the development on these designated sites, rather than to compensate for the impact after the event. Any schemes being conducted by other sectors cannot therefore be taken into account in mitigating for the proposed development.


    Natural England’s advice highlights in particular the need to consider the nutrient neutralisation requirements at a very early stage in the development process. We would recommend that consultation is initiated at the outset to ensure that this does not become an impediment to obtaining planning permission. Carrying out the development once planning is granted helps minimise the cost of meeting these obligations.

    How can Capsticks help?

    Our housing and regeneration team, one of the largest in the country, advises on all types of development transactions from forward funded schemes, section 106 developments and stock rationalisations to plot sales and general asset management work. We are experts on all aspects of planning law including s106 agreements, CIL advice, planning appeals, Compulsory Purchase Orders and all general planning law matters. If you would like to learn more about the content of this article, or need further advice on the issues addressed, please contact Spencer Vella Sultana or Suzanne Smith in our development and planning teams.