Following on from our previous article, “Habitats Regulations Assessment and Nutrient Neutrality”, which we published on our blog last year, in this month’s article we look at the recently updated guidance from Defra[1] surrounding nutrient pollution and the requirements for nutrient neutrality, and how this may affect your residential development.

What causes nutrient pollution and how is it harmful?
When we talk about nutrient pollution in this context, we are referring primarily to nitrogen and phosphorus and to the pollution of watercourses. The sources of nutrient pollution are predominantly from wastewater treatment works and agriculture. For the purpose of this post, which focuses on nutrient neutrality associated with residential development projects, we will be focusing on wastewater as the source of nutrient pollution.

Wastewater from water treatment works is released into rivers, that in turn flow into connected habitats and sites of nature conservation importance, such as wetlands, estuaries and marine environments. Pollution generated from wastewater can travel far from the source and adversely affect habitats and species that are of international importance.

Increased nutrient inputs can result in habitat degradation through processes such as eutrophication, which promotes the development of algal blooms by reducing oxygen content in waterbodies. This degradation has negative impacts for habitats and the species that rely on these habitats.

Nutrient neutrality and residential development
In accordance with national planning policy, case law and legislation, 32 local planning authorities were previously advised by Natural England that “where protected sites are in unfavourable condition due to excess nutrients, projects and plans should only go ahead if they will not cause additional pollution to sites”. This is achieved through nutrient neutrality, which means that new residential development needs to mitigate for the additional wastewater that would be created from new houses and the additional nutrient load. Mitigation typically involves the creation of new wetlands or buffer zones that remove nutrients from water, either on site or off site.

What are the recent updates to the guidance?
As a result of further research, Natural England have identified a further 20 protected sites that are being adversely impacted by nutrient pollution. This has led to Natural England recently advising a further 42 local planning authorities that their areas are covered by this advice, bringing the total number of planning authorities to 74.

What are the next steps?
The current status with regards to achieving nutrient neutrality lies with the development project in terms of undertaking nutrient neutrality calculations to work out the level of mitigation required and in most cases, finding the solution for this either on site or through offsetting.

Natural England is in the process of developing catchment-specific calculators, which will allow developers to calculate the amount of nutrient mitigation required. They are also developing “a framework for assessing the effectiveness of habitat restoration mitigation and an associated reference tool”. Catchment-wide approaches are also being developed which will supersede the project-by-project approach, whilst further measures seek to address the pollution issues at source.

[1] Defra (2022). Policy paper – Nutrient pollution: reducing the impact on protected sites. Published 16 March 2022.