The Solent’s Nitrate Mitigation Solution

Decoration Decoration

All development that would increase overnight stays in the Solent area must now demonstrate nutrient neutrality

Planner Insight
Policy & Legislation
South East
Author Kristina Wall
Principal Planner
Decoration Decoration

The Issue – Nitrate Pollution

Over the last two years we have seen a spike in development ‘moratoriums’ throughout the Solent area. The disruption is due to increasing concern for protected wildlife and the negative effect development can have on their environment. Housing growth had stalled with local planning authorities (LPAs) halting the determination of planning applications for any new development that facilitates overnight stays. This includes not only residential development but also uses such as hotels, tourist and student accommodation.

The issue for the planning system arose due to an excessive amount of nutrients, principally nitrogen, entering the Solent’s Special Protect Areas (SPA) and Special Areas of Conservation (SAC).  This pollution from Waste Water Treatment Works (WWTW) and other sources, such as agriculture, is causing eutrophication which leads to an increase in algae growth.  The influx is creating large algae mats, preventing oxygen from reaching animals in the sediment.  In turn, this is adversely affecting the food source of a large number of protected birds.

Nutrient Neutrality

The impact of nitrate pollution has been known for a while but over the past two years it has reached such significant levels that more drastic action has had to be taken.  Consequently, all development that would increase overnight stays in the Solent area must now demonstrate nutrient neutrality (i.e. they will not add to existing nutrient burdens) prior to planning permission being granted.

In June 2020 Natural England provided planning and environmental context to the nutrient neutrality approach, including the method for calculating nutrient budgets. They also clarified the areas of the Solent that are affected generally cover the following areas:

  • East Hampshire District
  • Isle of Wight
  • River Itchen catchment
  • New Forest
  • River Test catchment
  • Chichester Harbour catchment

The Solution – Mitigation

Rather frustratingly, but also understandably, it has taken some time to find a way forward.  However, a solution has been in found in the form of mitigation schemes which allow developers that are unable to offset the impact on site to make financial contributions to these schemes instead.  Simply put, the mitigation schemes secure agricultural land being taken out of intense farming thereby reducing nitrogen inputs.

Solent Nutrient Market Pilot

The Government have set up a pilot online ‘nitrate trading’ auction platform focused on South-East Hampshire.  The platform will enable developers to buy credits to create meadows, woodlands and wetlands, which will mitigate against the effect of their development.  Government is investing £3.9m in this scheme which could help inform wider work on environmental matters such as carbon offsetting and biodiversity net gain.  It is a scheme that, if successful, could be rolled out nationally and presents an opportunity for landowners to profit from nature-based projects on their land.

PUSH Mitigation Schemes

In December 2021, the Partnership for South Hampshire (PUSH) released a list of potential mitigation schemes that are actively promoting to the development market in the associated catchment areas. They include:

  • Chilgrove Farm
  • Eastleigh Borough Council Scheme (Bishopstoke)
  • Eastleigh Borough Council Scheme (Botley)
  • Hampshire and Isle of Wight Wildlife Trust (Isle of Wight Schemes)
  • Kings Manor
  • Roke Manor
  • Warnford Park Estate
  • Whitewool Steam Wetlands (Meon Springs)
  • Shalfleet Engineering Wetland

They cover a wide area across the Hampshire south coast meaning there may be schemes available for residential development in Eastleigh, Southampton, Portsmouth and the New Forest to offset potential residential development where on-site mitigation is not possible.

Offsetting Credits

These early schemes are going to be competitive with many developers looking to secure credits. The calculations to establish offsetting credits are complex and require liaison with specialists such as hydrologists and drainage consultants. Furthermore, some schemes may not be suitable for particular development projects, so liaison with Natural England is recommended.

Nevertheless, it is great to see more mitigation schemes coming forward and to hear that the list will be developed as more sites are made available. We are hopeful that as time goes on progress with a credit system (see Nutrient Market Pilot above) will catch up so that they are more accessible and simpler to purchase.


Most LPAs in the Solent Area are granting planning permission again but each of them is approaching mitigation and the associated credit slightly differently – and at very different speeds! Our local consultants work on a site by site basis and are able to advise on the feasibility of your proposals. For the time being, we are pleased to have the planning system back up and running in the area (for the most part).

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